Peptide-peptoid metal complexes

Abstract

A chemical complex comprising divalent metal ions, preferably Ca.sup.+2 ions, and peptide-peptoid trimers in a fixed ratio and having a centrosymmetric crystalline structure wherein three divalent metal ions at the interior of the complex are coordinated with the peptide carboxylate and urethane oxygen atoms. The globular complex has a hydrophobic outer surface and is useful as an ionophore.

Description

The invention relates to chemical complexes comprising peptides and divalent metal ions. Particularly it relates to multinuclear Ca.sup.2+ complexes of linear N-protected peptide derivatives comprising peptoid residues.

BACKGROUND OF THE INVENTION

Divalent cations such as Mg.sup.2+ or Ca.sup.2+ are known to be important in modulating the binding affinity of hormones such as oxytocin (Di Scala-Guenot, D. et al., Biochem. J. 284:499-505, 1992; Pearlmutter, A. F. et al. J. Biol. Chem. 254:3899-3906 1979; Pliska, V., et al. Biochem. J. 277:97-101, 1991); vasopressin (Di Scala-Guenot, D. et al., 1992; Pearlmutter, A. F. et al., 1979; Altura, B. M. et al. Am. J. Physiol. 228:1615-1620, 1996; and Gopalakrishnan, V. et al. Endocrinology 123:922-930, 1988); gastrin (Peggion, E. et al. Biopolymers 23:1225-1240, 1984); glucagon (Epand, R. M. Mol. Pharmacol. 22:105-108, 1982; and Brimble, K. S. et al. Biochemistry 32:1632-164, 1993); GnRH (Gerega, K. et al. J. Inorg. Biochem. 33:11-18, 1988); insulin (Hill, C. P. et al. Biochemistry 30:917-924, 1991); substance P (Ananthanarayanan, V. S. et al. Biopolymers 32:1765-1773, 1992); and bombesin (Saint-Jean, A., et al., Poster presentation at the 13th American Peptide Symposium, Edmonton, Canada, 1993). The cell receptors of these hormones are also known to bind Ca.sup.2+ (Williams, P. F. et al. Cell Calcium 11:547-556, 1990. Synthetic peptide-metal complexes are potentially useful in methods for intracellular delivery of these cations.

To date, only two crystal structures of synthetic Ca.sup.2+ -complexes with peptides have been reported and both of these crystal structures are of cyclic peptides (Seetharama Jois, D. S. et al. Int. J. Peptide Protein Res. 41:484-491, 1993 and Varughese, K. I. et al. Int. J. Peptide Protein Res. 27:118-122, 1986. In c(Ala-Leu-Pro-Gly).sub.2.Ca(ClO.sub.4).sub.2 (Seetharama Jois, D. S. et al., 1993), complexation occurs through an incomplete encapsulation of the metal ion by the peptide molecule, and in c(Pro-Gly).sub.3.Ca(ClO.sub.4).sub.2 (Varughese, K. I. et al., 1986), a complete encapsulation is found wherein two cyclic peptide molecules sandwich a Ca.sup.2+ ion. Solvent molecules occupy coordination sites in both of these crystal structures. Complexation of linear peptides to Ca.sup.2+ cations in solution has been studied by a variety of techniques, such as CD, NMR, and IR spectroscopies. It is desirable to synthesize other types of linear metal-peptide complexes having biologically useful applications.

SUMMARY OF THE INVENTION

According to the invention there is provided a chemical complex comprising three divalent metal ions independently selected from the group consisting of Ca.sup.2+, Mg.sup.2+, Fe.sup.2+ and Mn.sup.2+ and six linear, N-protected peptide-peptoid trimers. In one embodiment the chemical complex comprises three divalent metal ions selected from the group consisting of Ca.sup.2+, Mg.sup.2+, Fe.sup.2+ and Mn.sup.2+ coordinated to six linear, N-protected peptide-peptoid trimers wherein solvent molecules are not bound at the coordination sites. In a preferred embodiment the chemical complex comprises at least two species of linear N-protected peptide-peptoid trimers.

According to one aspect of this embodiment the peptoid residues of the chemical complex are N-substituted isomers of amino acids selected from the group consisting of glycine, valine, leucine, isoleucine, glutamine, lysine, phenylalanine and aspartic acid. Particularly the N-protected peptide-peptoid trimer is a Boc-Gly-AA-peptoid, a Boc-Gly-peptoid-AA or a Boc-Gly-dipeptoid, wherein the peptoid is selected from the group consisting of N-substituted isomers of glycine, valine, leucine, isoleucine, glutamine, lysine, phenylalanine, and aspartic acid.

According to another aspect of this embodiment the chemical complex comprises three divalent metal ions independently selected from the group consisting of Ca.sup.2+, Mg.sup.2+, Fe.sup.2+ and Mn.sup.2+ and six linear, N-protected Gly-dipeptoid trimers. In a preferred aspect of this embodiment the peptide-dipeptoid trimers are Gly-Nleu-Nleu.

According to yet another embodiment of the invention the chemical complex comprises three divalent metal ions independently selected from the group consisting of Ca.sup.2+, Mg.sup.2+, Fe.sup.2+ and Mn.sup.2+ and six linear, N-protected dipeptide-peptoid trimers. The dipeptide-peptoid trimers are Gly-Pro-Nleu or Gly-Nleu-Pro.

In a preferred aspect of this embodiment the chemical complex comprises N-protected dipeptide-peptoid trimers selected from the group consisting of

Boc-Gly-Pro-Nleu-O.sup.- Boc-Gly-Nleu-Pro-O.sup.- Boc-Gly-AA-Nleu-O.sup.- ; and Boc-Gly-Nleu-AA-O.sup.-

wherein AA is any selected substituted or unsubstituted .alpha.-amino acid residue whether naturally occurring or synthetic. For example, the chemical complex can be of the formula Ca.sup.2+.sub.3 (Boc-Gly-Pro-Nleu-O.sup.-).sub.6 or Ca.sup.2+.sub.3 (Boc-Gly-Nleu-Pro-O.sup.-).sub.6. For example, the chemical complex can have the formula M.sup.2+.sub.3 (Boc-Gly-Nleu-Nleu-O).sub.6, wherein M.sup.2+ is a divalent metal ion selected from the group consisting of Ca.sup.2+, Mg.sup.2+, Fe.sup.2+ or Mn.sup.2+ and Nleu is N-isobutylglycine. Particularly the calcium complex can have the formula Ca.sup.2+.sub.3 (Boc-Gly-Nleu-Nleu-O).sub.6, wherein Nleu is N-isobutylglycine.

According to yet another aspect of the invention the chemical complex has a globular centrosymmetric conformation, comprising three divalent metal ions and six N-protected peptide-peptoid trimers, wherein said divalent metal ions are in the central core of the globular complex, and the anionic carboxylate regions of said N-protected peptide-peptoid trimers face inwardly and the hydrophobic portions of said N-protected peptide-peptoid trimers face outwardly.

In a preferred aspect of this embodiment, the chemical complex has a globular centrosymmetric conformation, comprising three Ca.sup.++ ions and six N-protected peptide-peptoid trimers, wherein said calcium ions are in the central core of the globular complex, and the anionic carboxylate regions of said N-protected peptide-peptoid trimers face inwardly and the hydrophobic portions of said N-protected peptide-peptoid trimers face outwardly. Particularly, according to this aspect of the invention there is provided a chemical complex according to wherein one of said calcium ions is located at the center of symmetry and two of said calcium ions are located lateral thereto, and said central calcium ion is coordinated to six peptide-peptoid trimers through C-terminal carboxylate oxygens thereof and each said lateral calcium ions is coordinated to three of said peptoid-peptide trimers both through a carboxylate oxygen and a urethane oxygen thereof. In preferred aspects of this embodiment the chemical complex the six trimers are Boc-Gly-Nleu-Nleu-O and each trimer is coordinated to a lateral calcium ion through a first carboxylate oxygen and a urethane carbonyl oxygen and each said trimer is coordinated to the central calcium ion through a second carboxylate ion. Particularly the chemical complex has the formula Ca.sup.2+.sub.3 (Boc-Gly-Nleu-Nleu-O).sub.6, wherein Nleu is N-isobutylglycine. In one embodiment, the chemical complex can be globular complex wherein one side of the globular complex consists of structures of left-handed helicity and the opposite side consists of structures of right-handed helicity.

According to another aspect of the invention there is provided a chemical complex wherein the N-protecting group is a hydrophobic moiety selected from the group consisting of C.sub.6 -C.sub.24 alkyl groups, aromatic groups such as benzyl and conventional peptide blocking groups such as t-butyloxycarbonyl (tBoc), benzyloxycarbonyl, biphenylylisopropyloxycarbonyl (Bpoc), triphenylmethyl (trityl), 9-fluorenylmethyloxycarbonyl (Fmoc) and p-toluenesulfonyl groups. In a preferred embodiment of the invention, the side chains of the residues in each said linear N-protected peptide-peptoid trimer are achiral. Alternatively, the side chains of the residues in each said linear N-protected peptide-peptoid unit are chiral.

The advantage of the calcium-binding ligands is the simplicity of the ligand per se. The ligand is a peptide-dipeptoid trimer and the overall structure is achiral. There is no involvement of solvent ions in the X-ray crystal structure which suggests that the Boc-Gly-Nleu-Nleu-O.sup.- complex is a good calcium binder. In addition, since the ligands contain peptoid units, it is expected to be biostable. The Ca.sup.2+.sub.3 (Boc-Gly-Nleu-Nleu-O.sup.-).sub.6 complex has a hydrophobic periphery which suggests that is may be able to traverse a lipid membrane. The complex therefore serves as a model for the design of ionophores which can introduce metal cations into cells and organelles. Ionophores also have therapeutic potential since they have the ability to alter membrane permeability.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the structure of the Ca.sup.2+.sub.3 (Boc-Gly-Nleu-Nleu-O).sub.6 entity, where Nleu is N-isobutylglycine. Calcium ions and oxygen atoms are represented as hatched and crossed circles, respectively. The central calcium ion is positioned on a center of symmetry.

FIG. 2 shows the coordination of the oxygen atoms of the peptide-peptoid units to Ca.sup.2+ ions.

FIG. 3 shows the structure of the Boc-Gly-Nleu-Nleu-O.sup.- unit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

We have discovered that N-protected linear peptide-peptoid trimers can be ligands for small divalent metal ions, forming a complex in which the metal ions are tightly bound and solvent molecules such as H.sub.2 O are absent from the coordination sites.

The present invention is related to recently disclosed building blocks for collagen-like structures comprising peptidomimetic residues such as N-isobutylglycine (Nleu) (Melancini, G.; Feng, Y.; Goodman, M. J. Am. Chem. Soc. 1996, 118, 10725-10732; and Goodman, G.; Melacini, G.; Feng. Y. J. Am. Chem. Soc. 1996, 118, 10928-10929) and the synthesis of peptide-peptoid oligomers. The preparation and properties of these structures is disclosed in application Ser. No. 08/668,360 which is hereby incorporated by reference in its entirety. The structure of the peptoid residues in the linear peptide-peptoids of the invention can be any N-substituted amino acid with a hydrophobic R (side chain) group. That is, the peptoid may contain R groups that are hydrophobic side chains of amino acids (AA) or the R group could be any aliphatic chain or aromatic-containing side chain. Included within the scope of the invention are peptide-peptoid divalent metal binding ligands wherein the side chains of the peptide or peptoid residues are chiral or achiral. The metal ion can be any small divalent ion such as, for example, Fe.sup.+2, Ca.sup.+2 or Mg.sup.+2. The preferred ions are Mg.sup.+2 and Ca.sup.+2.

The peptoid residues of the trimers may be any N-substituted isomer of an amino acid, for example, glycine, valine, leucine, isoleucine, glutamine, lysine, phenylalanine or aspartic acid. The amino acid residue can be any substituted or unsubstituted .alpha.-amino acid residue whether naturally occurring or synthetic. The ligands also include not only peptide-dipeptoid trimers, but also dipeptide-peptoid trimers having a single peptoid residue. The peptide-peptoid trimers complexed with the metal ions may have identical or different peptide-peptoid sequences.

Preferably, the N-terminal blocked residue is glycine (Gly). For example, the invention includes the preferred blocked trimers:

Boc-Gly-peptoid-peptoid-O.sup.- Boc-Gly-peptoid-AA-O.sup.- Boc-Gly-AA-peptoid-O.sup.- Particularly preferred blocked trimers are: Boc-Gly-Pro-Nleu-O.sup.- Boc-Gly-Nleu-Pro-O.sup.- Boc-Gly-AA-Nleu-O.sup.- ; and Boc-Gly-Nleu-AA-O.sup.-

wherein AA is any selected .alpha.-amino acid residue whether naturally occurring or synthetic. Preferably the amino acid residue is proline.

The N-blocking group can be any hydrophobic moiety known to peptide chemists for blocking terminal amino groups of amino acids and peptides during solid phase peptide synthesis. Examples of suitable groups are for example, hydrophobic moieties selected from the group consisting of long chain C.sub.6 -C.sub.24 alkyl groups, aromatic groups such as benzyl, other complex groups bearing aromatic structures, as well as the conventional peptide blockers known to be useful, such as t-butyloxycarbonyl (tBoc), benzyloxycarbonyl, biphenylylisopropyloxycarbonyl (Bpoc), triphenylmethyl (trityl), 9-fluorenylmethyloxycarbonyl (Fmoc) and p-toluenesulfonyl groups. The N-blocking group is preferably a conventional tert-butyloxycarbonyl group.

As part of these studies Boc-Gly-Nleu-Nleu-OH (I) was synthesized and it was discovered that its ionized form complexes calcium ions. Accordingly, a preferred embodiment of the invention comprises a calcium complex of a linear peptide-like molecule and its crystalline structure. The structure of Ca.sup.2+.sub.3 (Boc-Gly-Nleu-Nleu-O.sup.-).sub.6, where Nleu denotes N-isobutylglycine, was determined by single crystal X-ray diffraction techniques. The calcium ions are completely encapsulated through the oxygen atoms of the N-protected glycyl-dipeptoid derivative, without any involvement of solvent molecules. The urethane and the two peptoid amide bonds of the glycyl dipeptoid molecule are in a trans, cis, and cis conformation, respectively. ##STR1##

The structure of Ca.sup.2+.sub.3 (Boc-Gly-Nleu-Nleu-O.sup.-).sub.6 (FIG. 1) was determined by single crystal X-ray diffraction techniques as described in the Experimental section. The calcium cations are completely encapsulated through oxygen atoms of the N-protected glycyl-dipeptoid derivative (FIG. 2) without any involvement of solvent molecules, although they are present in the unit cell. The experimental data also describes an extensive analysis of the conformation of the Nleu peptoid residue. The conformation of the glycyl-dipeptoid molecule is presented in FIG. 3.

In Ca.sup.2+.sub.3 (Boc-Gly-Nleu-Nleu-O.sup.-).sub.6, each glycyl-dipeptoid unit occupies a folded conformation and behaves as a bischelate toward a lateral calcium ion. The folding of the backbone chain, which results in coordination to the divalent cation, is made possible because of the cis conformation of the two tertiary amide linkages involving Nleu peptoid residues. All six independent N-protected trimer molecules have nearly the same conformation and the C-terminal groups exist as carboxylate anions in the crystal structure. Each trimer molecule acts as a bidentate ligand toward one lateral calcium cation, which coordinates one oxygen of the carboxylate group as well as the urethane carbonyl oxygen. The coordination at the bivalent ion resembles an octahedral complex. The trimer units are able to complex the central calcium ion through their second carboxylate oxygens. The central calcium ion is therefore coordinated to all six glycyl-dipeptoid units. The central calcium ion sits on the center of symmetry so that the resulting globular entity is centrosymmetric with one half of it consisting of structures of right-handed helicity and the other half consisting of structures of left-handed helicity. This arrangement is made possible because of the achiral nature of the three residues in each peptoid containing trimer. The globular entity, Ca.sup.2+.sub.3 (Boc-Gly-Nleu-Nleu-O.sup.-).sub.6, is rather hydrophobic on the surface where the methyl groups of the Boc termini and the isobutyl side chains are located. In the central core of the globular complex all of the charged carboxylate oxygen atoms are positioned. The central Ca.sup.2+ ion on the average shows Ca-O distances of 2.20 .ANG., while the lateral Ca.sup.2+ ion shows Ca-O distances of 2.35 .ANG. and 2.38 .ANG. with carboxylate and carbonyl oxygens, respectively.

The three independent achiral molecules coordinated to the lateral calcium ions have very similar conformational angles .phi.,.psi. and .omega.: Gly.sup.1 (.apprxeq.180.degree., .apprxeq.180.degree., .apprxeq.0.degree.), Nleu.sup.2 and Nleu.sup.3 residues (.apprxeq.-70.degree., .apprxeq.180.degree., .apprxeq.0.degree.) corresponding to right handedness. The centrosymmetric related molecules on the other side of the central calcium ion have opposite handedness with opposite conformational angles. The urethane and the two amide bonds along the chain are in a trans, cis, and cis conformation, respectively, with considerable deviation from planarity. Four of the six side chains of the independent Nleu peptoid residues have .chi..sup.1 and .chi..sup.2 values near -110.degree., 60.degree. (and 180.degree.) while the remaining two exhibit the opposite values: 110.degree., 60.degree. (and 180.degree.). The observed conformation of the Nleu peptoid residues corresponds to the minimum energy conformation cis .alpha..sub.D form found by others in ab initio calculations (Moehle, K., et al.(1996) Biopolymers 38:781-790. The trans conformation of the .phi. and .psi. angles allows for the onset of the intramolecular N--H . . . C.dbd.O hydrogen bond between the N--H and the C.dbd.O groups of the Gly residue (C.sub.5 -conformation), which are not involved in other intermolecular H-bond interactions. Hydrophobic intermolecular interactions allow for the packing of the Ca.sup.2+.sub.3 {Boc-Gly-Nleu-Nleu-O.sup.- }.sub.6 globular entities in the crystal.

The calcium complexing ligand was prepared by reacting Boc-Gly-Nleu-OH with Nleu-OEt using BOP (O-benzotriazolyl-N-oxytri-dimethylamino-phosphonium hexafluorophosphate) as the activating reagent to give Boc-Gly-Nleu-Nleu-OEt (Scheme 1). The trimer was then saponified with KOH in H.sub.2 O (containing calcium ions)-THF to afford the calcium complex of Boc-Gly-Nleu-Nleu-OH. The calcium ions in the water were sufficient to form the complex. Calcium complexing ligands containing other peptide-peptoid trimers can be prepared in the same manner by substituting the appropriate amino acid or peptoid molecule.

The particularly preferred peptoid-containing calcium ligand, Boc-Gly-Nleu-Nleu-O.sup.-, has a comparatively simple structure when compared to other calcium-binding peptides. The binding of peptoid-containing peptides to calcium is also not previously known. Because no solvent molecules coordinate with the calcium ion in the complex, the peptide-peptoid ligand appears to be extremely effective at binding calcium ions. It is believed that the cis configuration of the two peptoid amide bonds facilitates this chelation to calcium.

Other small divalent metal ions having about the same diameter as calcium are expected to complex with analogous peptide-peptoid trimers having similar physical characteristics in substantially the same structures and having the same proportion of peptide to metal compositions.

Experimental

The preparation of the compounds of the present invention is described in detail using the following examples, but the chemical reactions described are disclosed in terms of their general applicability to the preparation of the calcium-binding ligands of the invention. Occasionally, the reaction may not be applicable as described to each compound included within the disclosed scope of the invention. The compounds for which this occurs will be readily recognized by those skilled in the art. In all such cases, either the reactions can be successfully performed by conventional modifications known to those skilled in the art, that is, by appropriate protection of interfering groups, by changing to alternative conventional reagents, or by routine modification of reaction conditions. Alternatively, other reactions disclosed herein or otherwise conventional will be applicable to the preparation of the corresponding compounds of the invention. In all preparative methods, all starting materials are known or readily prepared from known starting materials; all temperatures are set forth in degrees Celsius; and, unless otherwise indicated, all parts and percentages are by weight.

Standard amino acids were purchased from Sigma, St. Louis, Mo. Crystals of Ca.sup.2+.sub.3 {Boc-Gly-Nleu-Nleu-O.sup.- }.sub.6.3 CH.sub.3 CN were grown from acetonitrile solutions. Solvent molecules are not shown in FIG. 1. The structure of Ca.sup.2+.sub.3 (Boc-Gly-Nleu-Nleu-O.sup.-).sub.6, C.sub.57 H.sub.102 N.sub.9 O.sub.18 Cal.sub.1.5.3 CH.sub.3 CN, F.W.=1384.77, was determined by single crystal X-ray diffraction techniques: Monoclinic P2.sub.1 /n, a=17.320(8), b=17.802(10), c=26.693(9), .beta.=97.47.degree. (3), Z=4, 10757 unique reflections, 3.degree.<2.theta.<45.degree., R=0.0941 for 6429 reflections with F.sub.o .gtoreq.4.0 .sigma.(Fo). All intensity measurements were recorded at 193 K, using graphite-monochromated MoK.alpha. radiation (.lambda.=0.71073) at a variable rate .omega. scan technique. The structure has been solved by direct methods and refined by full-matrix least squares. All calculations were performed using SHELXTL PLUS programs.

EXAMPLE 1

Preparation of Ca.sup.2+.sub.3 (Boc-Gly-Nleu-Nleu-O.sup.-).sub.6

The peptoid containing dimer, Boc-Gly-Nleu-OH (Feng, Y. B. (1996) Collagen-Based Biomaterials, University of California, San Diego), was allowed to react with Nleu-OEt using BOP (O-benzotriazolyl-N-oxytri-dimethylamino-phosphonium hexafluorophosphate) as the activating reagent to afford Boc-Gly-Nleu-Nleu-OEt (Scheme 1). The trimer was then saponified with KOH in H.sub.2 O (containing calcium ions)-THF to afford the calcium ion complex of Boc-Gly-Nleu-Nleu-OH. The calcium ions in the water were sufficient to form the complex. ##STR2##

Boc-Gly-Nleu-Nleu-OEt

A solution of Boc-Gly-Nleu-OH (26 g, 92 mmol) and HCl*Nleu-OEt (18 g, 92 mmol) was cooled to 0.degree. C. The coupling reagent, BOP (O-benzotriazolyl-N-oxytri-dimethylamino-phosphonium hexafluorophosphate, 41 g, 92 mmol), was then added portion-wise to the solution, followed by the addition of triethylamine (26 mL, 183 mmol). The ice bath was removed and the solution was left stirring overnight. The DMF was removed under reduced pressure and H.sub.2 O (800 mL) and EtOAc (800 mL) were added. The EtOAc layer was washed with H.sub.2 O (800 mL), NaHCO.sub.3 (2.times.800 mL), brine (800 mL), 2 N NaHSO.sub.4 (2.times.800 mL), and brine (3.times.800 mL). The organic layer was dried over anhydrous Na.sub.2 SO.sub.4 and the volatiles were removed by rotary evaporation under reduced pressure to give an oil. Purification via flash chromatography (SiO2, 1/1, hexanes/EtOAc) afforded 28 g (72% yield) of Boc-Gly-Nleu-Nleu-OEt. Rf=0.2 (1/1 hexanes/EtOAc). .sup.1 H NMR (300 MHz, CDCl.sub.3) .delta..sub.-- 5.49 (br s, 1H), 4.22-4.01 (m, 8 H), 3.19-3.06 (m, 4 H), 1.93-1.82 (m 2 H), 1.40 (s, 9 H), 1.24 (t, 3 H) 0.85-0.98 (m, 12 H).

FAD-MS: m/z=430 (M+H) calculated for C.sub.21 H.sub.39 N.sub.3 O.sub.6 429, found 430 (M+H).

Ca.sup.2+.sub.3 {Boc-Gly-Nleu-Nleu-O.sup.- }.sub.6

A solution of Boc-Gly-Nleu-Nleu-OEt (4.7 g, 11 mmol), H.sub.2 O (20 mL), and THF (20 mL) was cooled to 0.degree. C. KOH was dissolved in H.sub.2 O (6 mL) and was added slowly to the solution. The ice bath was removed and the solution was left stirring at room temperature for 30 min. The THF was then removed under reduced pressure and H.sub.2 O (30 mL) and EtOAc (80 mL) were added and the EtOAc layer separated. The H.sub.2 O layer was extracted with EtOAc further (2.times.80 mL). The EtOAc layers were pooled together and washed with brine (3.times.120 mL). The solution was then dried over Na.sub.2 SO.sub.4 and the solvent was removed by rotary evaporation. Purification via flash chromatography (SiO.sub.2, 1.5/1 EtOAc/MeOH) gave a white powder (4 g). Rf=0.3 (SiO.sub.2, 1.5/1 EtOAc/MeOH) Crystals were grown from a smaller portion of this material in acetonitrile solvent for X-ray crystallography.

Characterization of white powder:

.sup.1 H NMR (300 MHz, DMSO-d.sub.6) .delta. 6.64 (br s, 1 H), 4.14-2.99 (m, 10 H), 1.81-1.76 (m, 2H), 1.35 (s, 9 H), 0.77 -0.86 (m, 12 H). C.sub.38 H.sub.68 CaN.sub.6 O.sub.12 [Ca.sup.2+ (Boc-Gly-Nleu-Nleu-O.sup.-) fragment, M.sup.+ ]. MS-MALDI: 842 and 864 corresponding to M-(Ca.sup.2+.sub.2 (Boc-Gly-Nleu-Nleu-O.sup.-).sub.4 +H) and M-(Ca.sup.2+.sub.2 (Boc-Gly-Nleu-Nleu-O.sup.-).sub.4 +Na), respectively. Anal. Calcd for C.sub.114 H.sub.204 Ca.sub.3 N18O.sub.36 : C, 54.27, H, 8.15, N, 10.00, Ca, 4.77. Found: C, 54.18; H, 7.86; N, 9.78; Ca, 4.21.

______________________________________Structure Determination Summary______________________________________ Crystal Data Empirical Formula C .sub.57 H.sub.102 N.sub.9 O.sub.18 Ca.sub.1.5.3CH.sub.3 CN Color; Habit colorless glob Crystal size (mm) 0.4 .times. 0.7 .times. 0.7 Crystal System Monoclinic Space Group P2.sub.1 /n Unit Cell Dimensions a = 17.320(8) .ANG. b = 17.802(10) .ANG. c = 26.693(9) .ANG. .beta. = 97.470(0).degree. Volume 8160(7) .ANG..sup.3 Z 4 Formula weight 1384.77 Density (calc.) 1.127 Mg/m.sup.3 Absorption Coefficient 0.174 mm.sup.-1 F(000) 2844 Data Collection Diffractometer Used Siemens R3in/V Radiation Mok.alpha.( = 0.71073.ANG.) Temperature (K.) 193 Monochromator Highly oriented graphite crystal 2.theta. Range 3.0 to 45.00 Scan Type Wyckoff Scan Speed Variable; 5.00 to 10.000/min. in .omega. Scan Range (.omega.) 2.00.degree. Background Measurement Stationary crystal and stationary counter at beginning and end of scan; each for 25.0% of total scan time Standard Reflections 3 measured every 197 reflections Index Ranges -20 .ltoreq. h .ltoreq. 20, -19 .ltoreq. k .ltoreq. 0 -0 .ltoreq. 1 .ltoreq. 31 Reflections Collected 11073 Independent Reflections 10757 (R.sub.int = 2.02%) Observed Reflections 6429 (F > 4.0.sigma.(F)) Absorption Correction N/A Solution and Refinement System Used Siemens SHELXTL PLUS (PC Version) Solution Direct Methods Refinement Method Full-Matrix Least-Squares Quantity Minimized .SIGMA. w(F.sub.o - F.sub.c).sup.2 Absolute Structure N/A Extinction Correction N/A Hydrogen Atoms Riding model, fixed isotropic U Weighting Scheme w.sup.-1 = .sigma..sup.2 (F) + 0.0010F.sup.2 Number of Parameters Refined 685 Final R Indices (obs. data) R = 9.41%, wR = 11.75% R Indices (all data) R = 14.08%, wR = 24.80% Goodness-of-Fit 2.23 Largest and Mean .delta./.sigma. 3.213, 0.078 Data-to-Parameter Ratio 9.4:1 Largest Difference Peak .055 e.ANG..sup.3 Largest Difference Hole -0.90 e.ANG..sup.-3______________________________________ TABLE 1______________________________________Atomic/Coordinates (.times.10.sup.4) and equivalent isotropic displacement coefficient (.ANG..sup.2 .times. 10.sup.3) x y z U(eq)______________________________________Ca(1) 6184 (1) 2942 (1) 5378 (1) 41 (1) Ca(2) 5000 5000 5000 54 (1) O(5A) 8676 (8) 3066 (7) 5716 (4) 65 (3) C(1A) 8135 2620 6456 65 (3) C(2A) 9555 2488 6365 65 (3) C(3A) 8571 1718 5810 65 (3) C(4A) 8721 2479 6079 65 (3) O(SD) 8862 (8) 3116 (7) 5631 (5) 67 (3) C(1D) 8480 2539 6385 67 (3) C(2D) 9858 2501 6184 67 (3) C(3D) 8827 1756 5650 67 (3) C(4D) 8992 2484 5957 67 (3) C(6A) 8130 (6) 3235 (6) 5359 (3) 58 (4) O(7A) 7539 (4) 2854 (3) 5327 (2) 54 (2) N(8A) 8227 (4) 3841 (5) 5086 (3) 64 (3) C(9A) 7671 (5) 4069 (5) 4658 (3) 55 (3) C(10A) 8117 (6) 4338 (5) 4234 (3) S2 (3) O(11A) 8827 (4) 4388 (4) 4294 (2) 66 (3) N(12A) 7658 (4) 4516 (4) 3800 (2) 45 (3) C(13A) 8020 (5) 4636 (3) 3340 (3) 61 (4) C(14A) 7911 5443 3137 65 (4) C(15A) 8381 6008 3490 86 (5) C(16A) 8148 5497 2602 112 (6) C(17A) 6838 (5) 4367 (4) 3735 (3) 44 (3) C(18A) 6655 (5) 3550 (5) 3578 (3) 39 (3) 6(19A) 7179 (3) 3132 (3) 3493 (2) 54 (2) N(20A) 5894 (4) 3363 (3) 3505 (2) 38 (2) C(21A) 5300 (5) 3790 (4) 3730 (3) 39 (3) C(22A) 5347 (5) 3678 (4) 4301 (3) 34 (3) O(23A) 4821 (3) 4014 (3) 4505 (2) 44 (2) O(24A) 5882 (3) 3289 (3) 4522 (2) 40 (2) C(25A) 5685 (3) 2583 (2) 3382 (1) 44 (3) C(26A) 5400 2464 2816 46 (3) C(27A) 6052 2611 2489 57 (4) C(28A) 5077 1664 2724 65 (4) C(6B) 6105 1969 6507 60 (4) O(7B) 6264 2120 6097 58 (2) N(8B) 6030 2448 6897 58 (3) C(9B) 6108 3253 6806 54 (3) C(10B) 5928 (5) 3648 (5) 7281 (3) 5O (3) O(11B) 5760 (4) 3284 (3) 7647 (2) 66 (3) N(12B) 5953 (4) 4410 (3) 7269 (2) 48 (3) C(13B) 5824 (6) 4808 (10) 7718 (7) 46 (2) C(14B) 5029 5209 7656 46 (2) C(15B) 4922 5674 8127 46 (2) C(16B) 4364 4636 7546 46 (2) C(13E) 5867 (9) 4859 (18) 7723 (10) 108 (5) C(14E) 5043 4804 7879 108 (5) C(15E) 4983 5249 8366 108 (5) C(16E) 4432 5086 7451 108 (5) C(17B) 6212 (5) 4822 (4) 6853 (3) 45 (3) C(18B) 7086 (5) 4792 (4) 6875 (3) 48 (3) O(19B) 7505 (4) 4539 (3) 7245 (2) 64 (2) N(20B) 7403 (4) 5068 (4) 6467 (3) 47 (3) C(21B) 6905 (5) 5260 (4) 5999 (3) 45 (3) C(22B) 6594 (5) 4571 (6) 5689 (4) 56 (4) O(23B) 6200 (4) 4701 (4) 5260 (2) 76 (3) O(24B) 6745 (4) 3933 (4) 5872 (3) 71 (3) O(5C) 6080 (3) 1023 (3) 4249 (2) 64 (3) C(1C) 7403 1501 4338 80 (5) C(2C) 7022 287 3893 105 (6) C(3C) 7036 367 4834 110 (6) C(4C) 6876 805 4334 71 (4) C(6C) 5727 (7) 1467 (4) 4561 (3) 53 (4) O(7C) 6054 (4) 1771 (3) 4938 (2) 54 (2) N(8C) 4978 (5) 1523 (4) 4394 (3) 59 (3) C(9C) 4438 (5) 1972 (5) 4659 (3) 55 (4) C(10C) 3653 (7) 1884 (6) 4394 (5) 90 (5) O(11X) 3421 (9) 1333 (9) 4124 (6) 74 (4) O(11Y) 3620 (7) 1560 (7) 3930 (5) 51 (3) N(12X) 2973 (10) 2168 (10) 4677 (7) 63 (5) N(12Y) 3181 (9) 2339 (9) 4482 (6) 47 (4) C(13C) 2426 (10) 2400 (11) 4159 (10) 115 (5) C(14C) 1776 1913 4333 115 (5) C(15C) 981 2092 4029 115 (5) C(16C) 1966 1074 4286 115 (5) C(13F) 2186 (17) 2164 (16) 4414 (10) 158 (7) C(14F) 1804 1432 4568 158 (7) C(15F) 1124 1198 4170 158 (7) C(16F) 1520 1523 5087 158 (7) C(17C) 3213 (7) 2727 (6) 5030 (5) 99 (6) C(18C) 3400 (7) 2300 (5) 5530 (5) 82 (5) O(19X) 3481 (8) 1598 (8) 5627 (5) 59 (4) O(19Y) 3200 (8) 1628 (8) 5414 (5) 63 (4) N(20C) 3609 (5) 2713 (4) 5935 (3) 68 (4) C(21C) 3753 (6) 3516 (5) 5902 (3) 57 (4) C(22C) 4517 (6) 3722 (5) 5716 (3) 49 (3) O(23C) 4612 (4) 4420 (3) 5665 (2) 65 (3) O(24C) 4967 (4) 3215 (3) 5621 (2) 51 (2) C(25C) 3842 (13) 2293 (20) 6357 (7) 105 (5) C(26C) 3234 2326 6729 105 (5) C(27C) 3558 1994 7246 105 (5) C(28C) 2487 1910 6511 105 (5) C(25F) 4021 (12) 2397 (18) 6431 (7) 96 (5) C(26F) 3563 2289 6884 96 (5) C(27F) 4060 1889 7324 96 (5) C(28F) 2810 1843 6722 96 (5) N(1) 1806 (7) 4108 (6) 4963 (4) 91 (5) C(2) 1189 (8) 4043 (7) 5058 (4) 76 (5) C(3) 406 (7) 3987 (8) 5178 (5) 117 (7) N(4X) 6465 (11) 6692 (11) 7151 (8) 69 (5) N(4Y) 6452 (12) 6823 (13) 6897 (8) 85 (7) C(5) 6789 (7) 7300 (6) 7079 (5) 91 (5) C(6) 7220 (7) 8009 (6) 7135 (4) 92 (5) N(1H) 5521 (18) 7519 (17) 464 (7) 514 (34) C(2H) 5750 7481 879 417 (32) C(3H) 6039 7407 1418 283 (18) O(5B) 5790 (6) 1276 (5) 6675 (4) 51 (2) C(1B) 5323 604 5903 51 (2) C(2B) 5661 -54 6736 51 (2) C(3B) 6731 514 6307 51 (2) C(4B) 5878 602 6403 51 (2) O(5E) 6090 (5) 1257 (4) 6667 (3) 32 (2) C(1E) 5673 575 5892 32 (2) C(2E) 6023 -79 6725 32 (2) C(3E) 7077 544 6309 32 (2) C(4E) 6217 591 6396 32 (2) C(25X) 8203 5013 6444 100 C(26X) 8842 5610 6421 82 (9) C(27X) 8551 6400 6535 82 (9) C(28X) 9569 5411 6793 82 (9) C(25B) 8186 4914 6371 100 C(26B) 8700 5622 6381 82 (9) C(27B) 8802 5995 6905 82 (9) C(28B) 9500 5425 6224 82 (9) C(25E) 8224 (4) 4969 (4) 6435 (3) 59 (4) C(26E) 8709 5697 6458 90 (5) C(27E) 9572 5530 6428 68 (4) C(28E) 8623 6136 6945 68 (4)______________________________________ *Equivalent isotropic U defined as one third of the trace of the orthogonalized U.sub.ij tensor TABLE 2______________________________________Bond lengths (.ANG.)______________________________________ Ca(1)-Ca(2) 4.254 (3) Ca(1)-O(7A) 2.373 (7) Ca(1)-O(24A) 2.358 (5) Ca(1)-O(7B) 2.404 (4) Ca(1)-C(22B) 3.074 (11) Ca(1)-O(24B) 2.338 (7) Ca(1)-O(7C) 2.389 (5) Ca(1)-O(24C) 2.33S (7) Ca(2)-C(22A) 3.110 (8) Ca(2)-O(23A) 2.194 (S) Ca(2)-C(22B) 3.205 (9) Ca(2)-O(23B) 2.171 (6) Ca(2)-C(22C) 3.153 (9) Ca(2)-O(23C) 2.231 (6) Ca(2)-Ca(1A) 4.254 (3) Ca(2)-C(22D) 3.110 (8) Ca(2)-O(23D) 2.194 (5) Ca(2)-C(22E) 3.205 (9) Ca(2)-O(23E) 2.171 (6) Ca(2)-C(22F) 3.153 (9) Ca(2)-O(23F) 2.231 (6) O(5A)-O(5D) 0.427 (19) O(SD)-C(6A) 1.393 (16) C(6A)-O(7A) 1.223 (12) C(6A)-N(8A) 1.325 (13) N(8A)-C(9A) 1.453 (11) C(9A)-C(10A) 1.528 (13) C(10A)-O(11A) 1.223 (12) C(10A)-N(12A) 1.354 (11) N(12A)-C(13A) 1.466 (11) N(12A)-C(17A) 1.433 (11) C(17A)-C(18A) 1.536 (11) C(18A)-O(19A) 1.219 (11) C(18A)-N(20A) 1.348 (11) N(20A)-C(21A) 1.468 (11) N(20A)-C(25A) 1.462 (7) C(21A)-C(22A) 1.528 (10) C(22A)-O(23A) 1.272 (10) C(22A)-O(24A) 1.242 (9) C(6B)-O(5B) 1.443 (11) C(9B)-C(10B) 1.517 (9) C(10B)-O(11B) 1.239 (11) C(10B)-N(12B) 1.358 (10) N(12B)-C(13B) 1.434 (20) N(12B)-C(13E) 1.475 (29) N(12B)-C(17B) 1.451 (11) C(17B)-C(18B) 1.508 (13) C(18B)-O(19B) 1.232 (10) C(18B)-N(20B) 1.372 (12) N(20B)-C(21B) 1.464 (10) N(20B)-C(25X) 1.398 (7) N(20B)-C(25B) 1.438 (7) N(20B)-C(25E) 1.447 (11) C(21B)-C(22B) 1.536 (13) C(22B)-O(23B) 1.277 (11) C(22B)-O(24B) 1.251 (12) O(5C)-C(6C) 1.351 (11) C(6C)-O(7C) 1.216 (10) C(6C)-N(8C) 1.319 (14) N(8C)-C(9C) 1.479 (13) C(9C)-C(10C) 1.456 (15) C(10C)-O(11X) 1.253 (18) C(10C)-O(11Y) 1.361 (17) C(10C)-N(12X) 1.563 (23) C(10C)-N(12Y) 1.196 (20) N(12X)-C(13C) 1.625 (28) N(12X)-C(13F) 1.450 (32) N(12X)-C(17C) 1.395 (21) N(12Y)-C(13C) 1.473 (25) N(12Y)-C(13F) 1.736 (33) N(12Y)-C(17C) 1.611 (20) C(17C)-C(18C) 1.532 (17) C(18C)-N(20C) 1.320 (15) N(20C)-C(21C) 1.466 (11) N(20C)-C(25C) 1.3677 (27) C(21C)-C(22C) 1.517 (14) C(22C)-O(23C) 1.263 (10) C(22C)-O(24C) 1.241 (11) N(1)-C(2) 1.136 (18) C(2)-C(3) 1.437 (19) N(4X)-N(4Y) 0.713 (30) N(4X)-C(5) 1.246 (23) N(4Y)-C(5) 1.108 (25) C(S)-C(6) 1.463 (15) O(5B)-O(5E) 0.523 (14)______________________________________ TABLE 3 __________________________________________________________________________Bond angles (.degree.)__________________________________________________________________________Ca(2)-Ca(1)-O(7A) 119.6 (2) Ca(2)-Ca(1)-O(24A) 60.4 (1) O(7A)-Ca(1)-O(24A) 93.4 (2) Ca(2)-Ca(1)-O(7B) 133.6 (1) Ca(2)-Ca(1)-C(22B) 48.6 (2) O(7B)-Ca(1)-C(22B) 111.8 (2) Ca(2)-Ca(1)-O(24B) 68.7 (2) O(7B)-Ca(1)-O(24B) 91.8 (2) C(22B)-Ca(1)-O(24B) 21.7 (2) Ca(2)-Ca(1)-O(7C) 128.6 (1) .Ca(2)-Ca(1)-O(24C) 57.5 (1) O(7A)-Ca(1)-O(24C) 164.7 (2) O(24A)-Ca(1)-O(24C) 96.9 (2) O(7C)-Ca(1)-O(24C) 106.7 (2) Ca(1)-Ca(2)-C(22A) 50.6 (1) Ca(1)-Ca(2)-O(23A) 58.7 (1) C(22A)-Ca(2)-O(23A) 19.4 (2) Ca(1)-Ca(2)-C(22B) 46.1 (2) Ca(1)-Ca(2)-O(23B) 45.7 (2) C(22B)-Ca(2)-O(23B) 16.3 (3) Ca(i)-Ca(2)-C(22C) 52.6 (2) Ca(1)-Ca(2)-O(23C) 66.3 (2) C(22C)-Ca(2)-O(23C) 18.7 (2) Ca(1)-Ca(2)-Ca(1A) 180.0 (1) C(22A)-Ca(2)-Ca(1A) 129.4 (1) O(23A)-Ca(2)-Ca(1A) 121.3 (1) C(22B)-Ca(2)-Ca(1A) 133.9 (2) O(23B)-Ca(2)-Ca(1A) 134.3 (2) C(22C)-Ca(2)-Ca(1A) 127.4 (2) O(23C)-Ca(2)-Ca(1A) 113.7 (2) Ca(1)-Ca(2)-C(22D) 129.4 (1) Ca(1A)-Ca(2)-C(22D) 50.6 (1) Ca(1)-Ca(2)-O(23D) 121.3 (1) Ca(1A)-Ca(2)-O(23D) 58.7 (1) C(22D)-Ca(2)-O(23D) 19.4 (2) Ca(1)-Ca(2)-C(22E) 133.9 (2) Ca(1)-Ca(2)-O(23E) 134.3 (2) C(22E)-Ca(2)-O(23E) 16.3 (3) Ca(1)-Ca(2)-C(22F) 127.4 (2) Ca(1A)-Ca(2)-C(22F) 52.6 (2) Ca(1)-Ca(2)-O(23F) 113.7 (2) Ca(1A)-Ca(2)-O(23F) 66.3 (2) C(22F)-Ca(2)-O(23F) 18.7 (2) C(4A)-O(5A)-C(6A) 130.3 (7) O(SA)-C(6A)-O(7A) 116.8 (10) O(5D)-C(6A)-O(7A) 130.6 (10) O(5A)-C(6A)-N(8A) 117.6 (10) O(5D)-C(6A)-N(8A) 103.8 (9) O(7A)-C(6A)-N(8A) 125.3 (8) Ca(1)-O(7A)-C(6A) 141.7 (6) C(6A)-N(8A)-C(9A) 122.8 (8) N(8A)-C(9A)-C(10A) 108.8 (7) C(9A)-C(10A)-O(11A) 121.5 (8) C(9A)-C(10A)-N(12A) 114.1 (8) O(11A)-C(10A)-N(12A) 124.3 (9) C(10A)-N(12A)-C(13A) 118.9 (7) C(10A)-N(12A)-C(17A) 121.6 (7) C(13A)-N(12A)-C(17A) 116.7 (6) N(12A)-C(13A)-C(14A) 112.7 (4) N(12A)-C(17A)-C(18A) 111.9 (7) C(17A)-C(18A)-O(19A) 119.8 (8) C(17A)-C(18A)-N(20A) 115.8 (7) O(19A)-C(18A)-N(20A) 124.1 (7) C(18A)-N(20A)-C(21A) 122.5 (6) C(18A)-N(20A)-C(25A) 118.3 (6) C(21A)-N(20A)-C(25A) 114.7 (6) N(20A)-C(21A)-C(22A) 112.9 (6) Ca(2)-C(22A)-C(21A) 120.7 (5) Ca(2)-C(22A)-O(23A) 35.1 (3) C(21A)-C(22A)-O(23A) 114.7 (6) Ca(2)-C(22A)-O(24A) 109.1 (5) C(21A)-C(22A)-O(24A) 119.1 (7) O(23A)-C(22A)-O(24A) 126.2 (7) Ca(2)-O(23A)-C(22A) 125.5 (5) Ca(1)-O(24A)-C(22A) 131.6 (5) N(20A)-C(25A)-C(26A) 113.0 (2) O(7B)-C(6B)-O(5B) 128.2 N(8B)-C(6B)-O(SB) 102.7 Ca(1)-O(7B)-C(6B) 150.9 (1) N(8B)-C(9B)-C(10B) 106.4 (3) C(9B)-C(10B)-O(11B) 120.7 (7) C(9B)-C(10B)-N(12B) 115.7 (7) O(11B)-C(10B)-N(12B) 123.6 (8) C(10B)-N(12B)-C(13B) 117.8 (9) C(10B)-N(12B)-C(17B) 122.4 (7) C(13B)-N(12B)-C(17B) 119.2 (9) N(12B)-C(13B)-C(14B) 111.9 (5) N(12B)-C(17B)-C(18B) 111.2 (6) C(17B)-C(18B)-O(19B) 121.8 (8) C(17B)-C(18B)-N(20B) 117.3 (7) O(19B)-C(18B)-N(20B) 120.9 (8) C(18B)-N(20B)-C(21B) 120.6 (7) C(18B)-N(20B)-C(25B) 123.8 (6) C(21B)-N(20B)-C(25B) 110.9 (6) N(20B)-C(21B)-C(22B) 113.4 (7) Ca(1)-C(22B)-Ca(2) 85.3 (2) Ca(1)-C(22B)-C(21B) 162.0 (6) Ca(2)-C(22B)-C(21B) 109.5 (5) Ca(1)-C(22B)-O(23B) 81.3 (6) Ca(2)-C(22B)-O(23B) 28.5 (4) C(21B)-C(22B)-O(23B) 116.5 (8) Ca(1)-C(22B)-O(24B) 43.8 (5) Ca(2)-C(22B)-O(24B) 124.1 (6) C(21B)-C(22B)-O(24B) 118.4 (8) O(23B)-C(22B)-O(24B) 125.1 (9) Ca(2)-O(23B)-C(22B) 135.1 (6) Ca(1)-O(24B)-C(22B) 114.5 (6) C(4C)-O(5C)-C(6C) 124.7 (5) O(5C)-C(6C)-O(7C) 124.8 (10) O(SC)-C(6C)-N(8C) 109.8 (7) O(7C)-C(6C)-N(8C) 125.4 (9) Ca(1)-O(7C)-C(6C) 143.0 (5) C(6C)-N(8C)-C(9C) 122.3 (7) N(8C)-C(9C)-C(10C) 108.6 (8) C(18C)-N(20C)-C(21C) 121.8 (9) C(18C)-N(20C)-C(25C) 113.0 (15) C(21C)-N(20C)-C(25C) 123.5 (15) N(20C)-C(21C)-C(22C) 115.0 (8) Ca(2)-C(22C)-C(21C) 133.1 (6) Ca(2)-C(22C)-O(23C) 34.5 (4) C(21C)-C(22C)-O(23C) 113.9 (8) Ca(2)-C(22C)-O(24C) 100.2 (6) C(21C)-C(22C)-O(24C) 119.3 (8) O(23C)-C(22C)-O(24C) 126.8 (9) Ca(2)-O(23C)-C(22C) 126.8 (6) Ca(1)-O(24C)-C(22C) 145.3 (6) N(20C)-C(25C)-C(26C) 110.8 (11) N(1)-C(2)-C(3) 178.2 (14) N(4Y)-N(4X)-C(5) 62.0 (23) N(4X)-N(4Y)-C(5) 83.3 (25) N(4X)-C(5)-N(4Y) 34.7 (15) N(4X)-C(5)-C(6) 165.4 (15) N(4Y)-C(5)-C(6) 160.0 (17) C(6B)-O(5B)-C(4B)__________________________________________________________________________ 119.6 TABLE 4 __________________________________________________________________________Anisotropic displacement coefficients (A.sup.2 .times. 10.sup.3) U.sub.11 U.sub.22 U.sub.33 U.sub.12 U.sub.13 U.sub.23__________________________________________________________________________ Ca(1) (1) 69 28 (1) 25 (1) -3 (1) -4 (1) -1 (1) Ca(2) 71 (2) 46 (2) 42 (1) -1 (1) 3 (1) -2 (1) C(6A) 64 (7) 69 (7) 34 (5) 8 (6) -18 (5) -12 (5) O(7A) 69 (5) 51 (4) 39 (3) 5 (3) -6 (3) -6 (3) N(8A) 61 (6) 8S (6) 40 (4) -12 (5) -19 (4) 13 (4) C(9A) 44 (6) 72 (6) 48 (5) -3 (5) -2 (4) 0 (5) C(10A) 54 (7) 56 (6) 45 (5) -6 (5) 7 (5) -6 (4) O(11A) 44 (4) 90 (5) 63 (4) -10 (4) 4 (3) -3 (4) N(12A) 4S (5) 50 (4) 41 (4) -5 (4) 10 (3) -5 (3) C(13A) 75 (7) 71 (7) 41 (5) -14 (6) 25 (5) -2 (5) C(14A) 64 (7) 77 (7) 56 (6) -20 (6) 14 (5) 8 (5) C(15A) 112 (10) 74 (8) 72 (7) -29 (7) 8 (7) -3 (6) C(16A) 169 (13) 112 (10) 58 (7) -61 (10) 28 (8) 6 (7) C(17A) 56 (6) 41 (5) 35 (4) -3 (4) 1 (4) -2 (4) C(18A) 45 (6) 46 (5) 25 (4) 4 (5) 5 (4) -1 (4) O(19A) 51 (4) S7 (4) 53 (4) 4 (3) 5 (3) -2 (3) N(20A) 49 (5) 35 (4) 28 (3) -2 (3) 3 (3) -3 (3) C(21A) 48 (5) 40 (5) 27 (4) 2 (4) 3 (4) 2 (4) C(22A) 45 (5) 28 (4) 36 (4) 0 (4) 4 (4) -1 (4) O(23A) 52 (4) 44 (3) 35 (3) 5 (3) 5 (3) -1 (3) O(24A) 58 (4) 35 (3) 24 (3) 7 (3) -1 (3) 0 (2) C(25A) 61 (6) 34 (4) 37 (4) -3 (4) 6 (4) 5 (4) C(26A) 53 (6) 46 (5) 37 (4) -2 (4) -1 (4) -8 (4) C(27A) 73 (7) 62 (6) 39 (5) 5 (5) 13 (5) -7 (4) C(28A) 80 (8) 46 (6) 68 (6) -2 (5) 5 (5) -18 (5) C(6B) 95 (8) 32 (5) 50 (6) -5 (5) -4 (5) 8 (4) O(7B) 113 (6) 29 (3) 30 (3) -5 (3) -6 (3) 7 (3) N(8B) 107 (7) 22 (4) 45 (4) 3 (4) 6 (4) -4 (3) C(9B) 90 (8) 25 (4) 43 (5) 1 (5) -6 (5) -1 (4) C(10B) 64 (7) 37 (5) 44 (5) 3 (5) -9 (5) 0 (4) O(11B) 116 (6) 32 (3) 51 (4) -4 (4) 9 (4) 0 (3) N(12B) 71 (5) 30 (4) 40 (4) 1 (4) 0 (4) C(17B) 52 (6) 32 (5) 47 (5) -5 (4) -10 (4) -1 (4) C(18B) 58 (6) 31 (5) 52 (5) -6 (4) -7 (5) O (4) O(19B) 62 (4) 61 (4) 63 (4) 4 (3) -21 (3) 15 (3) N(20B) 49 (5) 35 (4) SO (4) -5 (4) -10 (4) -5 (3) C(21B) 56 (6) 41 (5) 35 (4) -3 (4) -9 (4) -6 (4) C(22B) 40 (6) 66 (7) 62 (6) 2 (5) 3 (5) -27 (5) O(23B) 56 (4) 110 (6) 57 (4) 8 (4) -7 (4) -44 (4) O(24B) 75 (5) 47 (4) 89 (5) -3 (4) 4 (4) O(5C) 94 (6) 46 (4) 48 (4) -5 (4) 2 (4) -12 (3) C(1C) 97 (9) 65 (7) 72 (7) 10 (6) -13 (6) -4 (6) C(2C) 155 (13) 88 (9) 74 (8) 21 (8) 23 (8) -36 (7) C(3C) 185 (14) 65 (8) 78 (8) 48 (8) 7 (9) 11 (6) C(4C) 108 (10) 46 (6) 58 (6) 15 (6) 3 (6) -5 (5) C(6C) 99 (9) 24 (4) 34 (5) -11 (5) S (5) -1 (4) O(7C) 96 (5) 28 (3) 34 (3) -1 (3) -6 (3) -1 (3) N(8C) 84 (7) 46 (5) 46 (4) -16 (5) 7 (5) -6 (4) C(9C) 76 (7) 41 (5) 49 (5) -16 (5) 5 (5) -9 (4) C(10C) 103 (10) 47 (6) 106 (9) 9 (6) -38 (8) -34 (6) C(17C) 103 (10) 58 (7) 125 (11) 24 (7) -31 (8) -44 (7) C(18C) 93 (9) 27 (5) 129 (11) -2 (6) 29 (8) -10 (6) N(20C) 88 (7) 37 (5) 83 (6) -7 (4) 30 (5) 6 (4) C(21C) 78 (7) 41 (5) 54 (6) -1 (5) 19 (5) 2 (4) C(22C) 80 (8) 38 (5) 28 (4) -11 (5) 3 (5) 1 (4) O(23C) 109 (6) 31 (3) 58 (4) -19 (4) 25 (4) -6 (3) O(24C) 70 (5) 44 (4) 41 (3) -6 (3) 12 (3) 0 (3) N(1) 95 (8) 95 (8) 86 (7) 15 (7) 18 (7) -13 (6) C(2) 80 (9) 89 (8) 59 (7) S (8) 7 (7) -14 (6y C(3) 94 (11) 158 (14) 98 (10) -5 (10) 12 (8) -10 (9.) C(5) 68 (8) 59 (7) 141 (11) 2 (6) -9 (8) -48 (8). C(6) 97 (9) 68 (7) 100 (9) -11 (7) -31 (7) -12 (7) N(1H) 575 (66) 288 (41) 741 (64) 40 (39) 319 (51) 106 (42) C(2H) 242 (38) 79 (15) 1012 (85) 15 (21) 392 (50) 89 (40) C(3H) 183 (23) 511 (46) 144 (18) -63 (26) -22 (16) -58 (24) C(25E) 53 (6) 49 (6) 72 (6) 1 (5) -1 (5) -3 (5) C(26E) 65 (8) 84 (9) 121 (10) -6 (7) 18 (7) -12__________________________________________________________________________ (8) The anisotropic displacement exponent takes the form: -.sup.2 (h.sup. a*.sup.2 U.sub.11 + . . . + 2hka*b*U.sub.12) TABLE 5______________________________________ H-Atomcoordinates (.times.10.sup.4) and isotropic displacement coefficients (.ANG..sup.2 .times.]10.sup.3) x y z U______________________________________HH(1AA) 7616 2614 6280 65 (3) HH(1AB) 8187 2233 6709 65 (3) H(1AC) 8238 3100 6615 65 (3) H(2AA) 9650 2962 6.533 65 (3) H(2AB) 9611 2091 6610 65 (3) H(2AC) 9923 2418 6129 65 (3) H(3AA) 8053 1710 5633 65 (3) H(3AB) 8940 1647 5576 65 (3) H(3AC) 8628 1321 6056 65 (3) H(1DA) 7941 2528 6244 67 (3) H(1DB) 8589 2122 6611 67 (3) H(1DC) 8590 3000 6567 67 (3) H(2DA) 9963 2955 6376 67 (3) H(2DB) 9970 207S 6402 67 (3) H(2DC) 10179 2484 5917 67 (3) H(3DA) 8288 1744 55o8 67 (3) H(3DB) 9148 1740 5383 67 (3) H(3DC) 8939 1330 5868 67 (3) H(8AA) 8658 4121 5165 70 H(9AA) 7346 4464 4757 70 H(9AB) 7346 3650 4543 70 H(13A) 7793 4292 3086 70 H(13B) 8567 4527 3406 70 H(14A) 7369 5571 3118 70 H(15A) 8302 6505 3354 70 H(15B) 8210 5988 3818 70 H(15C) 8924 5883 3519 70 H(16A) 8077 6003 2480 70 H(16B) 8685 5357 2612 70 H(16C) 7830 5163 2380 70 H(17A) 6583 4699 3482 70 H(17B) 6635 4468 4046 H(21A) 4793 3642 3572 70 H(21B) 5365 4313 3659 70 H(25A) 5281 2433 3575 70 H(25B) 6127 2264 3478 70 H(26A) 4985 2813 2718 70 H(27A) 5855 2S32 2140 70 H(27B) 6230 3119 2536 70 H(27C) 6476 2272 2586 70 H(28A) 4901 1598 2371 70 H(28B) 5479 1305 2830 70 H(28C) 4649 1589 2914 70 H(9BA) 5749 3408 6521 80 H(9BB) 6629 3359 6741 80 H(13A) 6232 5174 7781 80 H(13B) 5858 4478 8004 80 H(14A) 5009 5544 7372 80 H(15A) 4423 5918 8078 100 H(1SB) 4950 5350 8416 100 H(15C) 5325 6047 8182 100 H(16A) 3873 4894 7508 100 H(16B) 4420 4369 7240 100 H(16C) 4384 4287 7821 100 H(13C) 5989 5379 7678 80 H(13D) 6235 4665 7992 80 H(14B) 4937 4285 7941 80 H(15D) 4466 5204 8454 100 H(1SE) 5349 5051 8635 100 H(15F) 5099 5768 8313 100 H(16D) 3923 5048 7553 100 H(16E) 4539 5601 7376 100 H(16F) 4455 4786 7154 100 H(17A) 6048 5336 6866 80 H(17B) 5974 4609 6540 80 H(21A) 7204 5558 5794 80 H(21B) 6478 S563 6078 80 H(1CA) 7313 1825 4613 100 H(1CB) 7939 1347 4380 100 H(1CC) 7286 1767 4024 100 H(2CA) 6923 559 3580 100 H(2CB) 7554 120 3941 100 H(2CC) 6682 -139 3882 100 H(3CA) 6945 687 5109 100 H(3CB) 6695 -60 4823 100 H(3CC) 7567 199 4882 100 H(9CA) 4587 2492 4669 80 H(9CB) 4454 1793 4999 80 H(13A) 2519 2272 3823 115 (5) H(13B) 2306 2925 4173 115 (5) H(14A) 1745 2021 4682 115 (5) H(15A) 588 1781 4145 115 (5) H(15B) 857 2611 4074 115 (5) H(15C) 1003 1996 3677 115 (5) H(16A) 1556 777 4396 115 (5) H(16B) 2013 957 3940 115 (5) H(16C) 2448 962 4493 115 (5) H(13A) 2596 2039 4218 158 (7) H(13B) 1805 2452 4203 158 (7) H(14A) 2188 1040 4593 158 (7) H(15A) 897 742 4275 158 (7) H(15B) 737 1587 4135 158 (7) H(15C) 1312 1118 3851 158 (7) H(16A) 1284 1063 5178 158 (7) H(16B) 1955 1640 5336 158 (7) H(16C) 1146 1922 5072 158 (7) H(17A) 2766 3041 5047 80 H(17B) 3650 3046 4996 80 H(21A) 3750 3730 6232 80 H(21B) 3336 3741 5680 80 H(25A) 4280 2593 6494 80 H(25D) 4021 1783 6346 80 H(26A) 3104 2844 6777 80 H(27A) 3168 2022 7469 100 H(27B) 3700 1479 7204 100 H(27C) 4009 2274 7386 100 H(28A) 2114 1936 6747 100 H(28B) 2273 2141 6198 100 H(28C) 2607 1394 6452 100 H(25B) 4507 2642 6543 80 H(25C) 4133 1916 6296 80 H(26B) 3422 2775 6998 80 H(27E) 3760 1829 7599 100 H(27F) 4214 1405 7214 100 H(27G) 4514 2185 7432 100 H(28E) 2532 1780 7007 100 H(28F) 2492 2112 6461 100 H(28G) 2940 1359 6597 100 H(3A) 314 3508 5324 100 H(3B) 312 4379 5409 100 H(3C) 61 4048 4868 100 H(6A) 7455 8134 6839 100 H(6B) 6859 8396 7198 100 H(6C) 7617 7966 7420 100 H(1BA) 5456 1011 5695 51 (2) H(1BB) 5369 137 5730 51 (2) H(1BC) 4797 665 5973 51 (2) H(2BA) 5129 -1 6796 51 (2) H(2BB) 5723 -522 6567 51 (2) H(2BC) 5995 -47 7052 51 (2) H(3BA) 6868 921 6100 51 (2) H(3BB) 7065 521 6624 51 (2) H(3BC) 6793 46 6138 51 (2) H(1EA) 5792 991 5686 32 (2) H(1EB) 5746 113 5718 32 (2) H(1EC) 5142 611 5956 32 (2) H(2EA) 5487 -52 6779 32 (2) H(2EB) 6113 -541 6555 32 (2) H(2EC) 6349 -61 7044 32 (2) H(3EA) 7199 960 6104 32 (2) H(3EB) 7403 562 6629 32 (2) H(3EC) 7166 82 6140 32 (2) H(25B) 8310 4693 6138 68 (4) H(25C) 8404 4665 6723 68 (4) H(26B) 8514 6005 6174 68 (4) H(27D) 9859 5992 6443 68 (4) H(27E) 9775 5214 6705 68 (4) H(27F) 9621 5279 6115 68 (4) H(28D) 8927 6587 6954 68 (4) H(28E) 8085 6262 6950 68 (4) H(28F) 8802 5831 7233 68 (4)______________________________________

The above described preferred calcium complexes of the invention, having novel glycyl-dipeptoid ligands as well as novel glycyl-peptide-peptoid ligands, each possessing three oxygen coordination sites, has applications in coordination chemistry and also for the design of new calcium ionophores. The use of these ionophores can probe the mechanism of ion transport through membranes and are means by which Ca.sup.2+ can be introduced into biological cells and organelles and its rate of influx controlled. Such ionophores are also useful as time release storage depots in addition to having the ability to treat disease states by the alteration of membrane permeability. There will be various modifications, improvements and applications of the disclosed invention that will be apparent to those skilled in the art, and the present application is intended to cover such embodiments. Although the present invention has been described in terms of certain preferred embodiments, it is intended that the full scope of the disclosure be measured only by reference to the following claims.

Claims

1. A chemical complex comprising three divalent metal ions selected from the group consisting of Ca.sup.2+, Mg.sup.2+, Fe.sup.2+ and Mn.sup.2+ and six linear, N-protected peptide-peptoid trimers.

2. A chemical complex consisting of three divalent metal ions selected from the group consisting of Ca.sup.2+, Mg.sup.2+, Fe.sup.2+ and Mn.sup.2+ coordinated to six linear, N-protected peptide-peptoid trimers wherein solvent molecules are not bound at the coordination sites.

3. A chemical complex according to claim 1 comprising at least two species of linear N-protected peptide-peptoid trimers.

4. A chemical complex according to any one of claims 1, 2 or 3 wherein the peptoid residues are N-substituted isomers of amino acids selected from the group consisting of glycine, valine, leucine, isoleucine, glutamine, lysine, phenylalanine and aspartic acid.

5. A chemical complex according to claim 1 wherein the N-protected peptide-peptoid trimer is a Boc-Gly-AA-peptoid, a Boc-Gly-peptoid-AA or a Boc-Gly-dipeptoid, wherein the peptoid is selected from the group consisting of N-substituted isomers of glycine, valine, leucine, isoleucine, glutamine, lysine, phenylalanine, and aspartic acid.

6. A chemical complex according to claim 1 comprising three divalent metal ions selected from the group consisting of Ca.sup.2+, Mg.sup.2+, Fe.sup.2+ and Mn.sup.2+ and six linear, N-protected Gly-dipeptoid trimers.

7. A chemical complex according to claim 6 wherein the peptide-dipeptoid trimers are Gly-Nleu-Nleu.

8. A chemical complex according to claim 1 comprising three divalent metal ions selected from the group consisting of Ca.sup.2+, Mg.sup.2+, Fe.sup.2+ and Mn.sup.2+ and six linear, N-protected dipeptide-peptoid trimers.

9. A chemical complex according to claim 8 wherein the dipeptide-peptoid trimers are Gly-Pro-Nleu or Gly-Nleu-Pro.

10. A chemical complex according to claim 1 comprising N-protected dipeptide-peptoid trimers selected from the group consisting of

Boc-Gly-Pro-Nleu-O.sup.-

Boc-Gly-Nleu-Pro-O.sup.-

Boc-Gly-AA-Nleu-O.sup.- ; and

Boc-Gly-Nleu-AA-O.sup.-

wherein AA is any selected substituted or unsubstituted .alpha.-amino acid residue whether naturally occurring or synthetic.

11. A chemical complex according to claim 1 of the formula Ca.sup.2+.sub.3 (Boc-Gly-Pro-Nleu-O.sup.-).sub.6 or Ca.sup.2+.sub.3 (Boc-Gly-Nleu-Pro-O.sup.-).sub.6.

12. A chemical complex according to claim 1 of the formula M.sup.2+.sub.3 (Boc-Gly-Nleu-Nleu-O).sub.6, wherein M.sup.2+ is a divalent metal ion selected from the group consisting of Ca.sup.2+, Mg.sup.2+, Fe.sup.2+ or Mn.sup.2+ and Nleu is N-isobutylglycine.

13. A calcium complex according to claim 1 of the formula Ca.sup.2+.sub.3 (Boc-Gly-Nleu-Nleu-O).sub.6, wherein Nleu is N-isobutylglycine.

14. A chemical complex according to claim 1 having a globular centrosymmetric conformation, comprising three divalent metal ions and six N-protected peptide-peptoid trimers, wherein said divalent metal ions are in the central core of the globular complex, and the anionic carboxylate regions of said N-protected peptide-peptoid trimers face inwardly and the hydrophobic portions of said N-protected peptide-peptoid trimers face outwardly.

15. A chemical complex according to claim 1 having a globular centrosymmetric conformation, comprising three Ca.sup.++ ions and six N-protected peptide-peptoid trimers, wherein said calcium ions are in the central core of the globular complex, and the anionic carboxylate regions of said N-protected peptide-peptoid trimers face inwardly and the hydrophobic portions of said N-protected peptide-peptoid trimers face outwardly.

16. A chemical complex according to claim 15 wherein one of said calcium ions is located at the center of symmetry and two of said calcium ions are located lateral thereto, and said central calcium ion is coordinated to six peptide-peptoid trimers through C-terminal carboxylate oxygens thereof and each said lateral calcium ions is coordinated to three of said peptoid-peptide trimers both through a carboxylate oxygen and a urethane oxygen thereof.

17. A chemical complex according to claim 15 wherein the six trimers are Boc-Gly-Nleu-Nleu-O and each trimer is coordinated to a lateral calcium ion through a first carboxylate oxygen and a urethane carbonyl oxygen and each said trimer is coordinated to the central calcium ion through a second carboxylate ion.

18. A chemical complex according to claim 16 or 17 having the formula Ca.sup.2+.sub.3 (Boc-Gly-Nleu-Nleu-O).sub.6, wherein Nleu is N-isobutylglycine.

19. A complex according to claim 15 or 16 wherein one side of the globular complex consists of structures of left-handed helicity and the opposite side consists of structures of right-handed helicity.

20. A chemical complex according to claim 1 wherein the N-protecting group is a hydrophobic moiety selected from the group consisting of C.sub.6 -C.sub.24 alkyl groups, aromatic groups such as benzyl and conventional peptide blocking groups such as t-butyloxycarbonyl (tBoc), benzyloxycarbonyl, biphenylylisopropyloxycarbonyl (Bpoc), triphenylmethyl (trityl), 9-fluorenylmethyloxycarbonyl (Fmoc) and p-toluenesulfonyl groups.

21. A complex according to claim 1 wherein the side chains of the residues in each said linear N-protected peptide-peptoid trimer are achiral.

22. A complex according to claim 1 wherein the side chains of the residues in each said linear N-protected peptide-peptoid unit are chiral.