In-situ solvent recycling process for solid phase peptide synthesis at elevated temperatures

Abstract

An improvement of deprotection in solid phase peptide synthesis is disclosed. The method includes the steps of adding the deprotection composition in high concentration and small volume to the mixture of the coupling solution, the growing peptide chain, and any excess activated amino acid from the preceding coupling cycle; and without any draining step between the coupling step of the previous cycle and the addition of the deprotection composition for the successive cycle; and with the coupling solution at a temperature of at least 30° C.

Description

This application incorporates by reference the sequence listing submitted on Jun. 19, 2018 in ASCII text file format in accordance with 37 CFR 1.824(a) titled “20180619_amended_sequence_listing” created on Jun. 19, 2018 with a file size of 8 KB. The sequence listing is part of the specification and is herein incorporated by reference in its entirely. In accordance with 37 CFR 1.825(a), the sequence listing contains no new matter.

BACKGROUND

Bruce Merrifield's pioneering development of solid phase peptide synthesis created a useful process for synthesis peptide chains through its use of filtration to remove reagents between steps. The process has involved repetitive cycles which include coupling and deprotection with washing and filtration in-between each step (FIG. 1). It has commonly been assumed that washing is required between each step to completely remove the reagents previously used so that they don't undesirably participate in the next step. This typically involves “insertions” which refer to the incorporation of an extra amino acid. This is thought to occur through either residual base removing the protecting group (Fmoc) on an amino acid recently coupled thereby allowing a second amino acid to “insert”; or through residual activated amino acid left behind during the subsequent deprotection step which could couple to deblocked sites thereby “inserting” an extra amino acid from the previous step. It was recently shown, however, that washing after the coupling step was not required for the successful synthesis of peptides. In this work the coupling step was drained and the deprotection solution was subsequently added to the vessel (J. Collins, K. Porter, S. Singh and G. Vanier, “High-Efficiency Solid Phase Peptide Synthesis (HE-SPPS),” Org. Lett., vol. 16, pp. 940-943, 2014) (FIG. 2).

SUMMARY

The invention is a method of deprotection in solid phase peptide synthesis in which the improvement comprises adding the deprotection composition in high concentration and small volume to the mixture of the coupling solution, the growing peptide chain, and any excess activated amino acid from the preceding coupling cycle; and without any draining step between the coupling step of the previous cycle and the addition of the deprotection composition for the successive cycle; and with the coupling solution at least 30° C.

In another aspect the invention is a method of deprotection in solid phase peptide synthesis in which the improvement comprises adding the deprotection composition in high concentration and small volume to the mixture of the coupling solution, the growing peptide chain, and any excess activated amino acid from the preceding coupling cycle; and without any draining step between the coupling step of the previous cycle and the addition of the deprotection composition for the successive cycle which removes at least 50% of the volume of the previous cycle coupling solution; and with the coupling solution at a temperature of at least 30° C.

The foregoing and other objects and advantages of the invention and the manner in which the same are accomplished will become clearer based on the followed detailed description taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a traditional SPPS Cycle

FIG. 2 illustrates more recent SPPS Cycles for High Efficiency Solid Phase Peptide Synthesis (HE-SPPS)

FIG. 3 illustrates in-situ solvent recycling process for solid phase peptide synthesis.

DETAILED DESCRIPTION

This invention presents a novel process whereby the coupling and deprotection steps occur within the same solvent. In this process concentrated base is added directly to the resin coupling solution after a desired period of time for the coupling to occur. The deprotection step is then immediately started when the base is added. Therefore, the onset of the deprotection step is immediately after the coupling step without any time delay.

Additionally, only a small volume of base is required since it can use the solvent present from the coupling reaction. This requires a sophisticated reagent delivery system for the base that is accurate at very small volumes (0.5 mL) with rapid delivery. Typically, a 20% solution of base (piperidine) in solvent is used for the deprotection step. Excess base concentration can increase base-catalyzed side reactions and therefore significant solvent is required. This means that significant solvent can be saved from this process by adding concentrated base to the coupling solvent.

To demonstrate the effectiveness of this new process a batch of 24 peptides were assembled using an automated peptide synthesizer modified to perform the in-situ solvent recycling step during each cycle.

Materials and Methods:

All peptides were synthesized using a LIBERTY BLUE™ PRIME™ system (CEM Corp., Matthews, N.C., USA) allowing for automated in-situ solvent recycling and evaporation based washing. The peptides were synthesized at 0.05 mmol scale with 10 equivalents of amino acid using CarboMAX™ coupling with amino acid/carbodiimide/ethyl 2-cyano-2-(hydroxyimino)acetate (AA/DIC/Oxyma) (1:2:1) based activation for 100 sec at 90° C. (E. Atherton, N. L. Benoiton, E. Brown, R. Sheppard and B. J. Williams, “Racemization of Activated, Urethane-protected Amino-acids by p-Dimethylaminopyridine. Significance in Solid Phase Peptide Synthesis,” J.C.S. Chem. Comm., pp. 336-337, 1981). ProTide resins (CEM Corp.) based on TentaGel® technology were used for synthesis with either a Rink Amide linker or a Cl-TCP(Cl) linker with unactivated loading of the first amino acid with DIEA at 90° C. for 5 min. The deprotection step was performed for 50 sec at 95° C. and initiated by adding 0.5 mL of 50% pyrrolidine directly to the coupling solution. A single 1×4 mL wash was used in between the deprotection and coupling steps. Peptides were cleaved with Trifluoroacetic acid (TFA)/triisopropylsilane/water/2,2′-(ethylenedioxy)diethanethiol (TFA/TIS/H₂O/DODt) (92.5:2.5:2.5:2.5) for 30 min at 38° C. using a RAZOR™ cleavage system (CEM Corp.).

Results and discussion:

TABLE 1
Automated Sequential Batch Synthesis of 24 Peptides
			Resin	UPLC	Synthesis
#	Peptide	Disease Area	Used	Purity	Time
1	GRP (SEQ ID NO: 1)	Regulates	RA	81	1:22
	VPLPAGGGTVLTKMYPRGNHWAVGHLM-NH2	Gastrin Release	ProTide
2	Glucagon (SEQ ID NO: 2)	Hypoglycemia	RA	75	1:28
	H-HSQGTFTSDYSKYLDSRRAQDFVQWLMNT-NH2		ProTide
3	Bivalirudin (SEQ ID NO: 3)	Blood thinner	Cl-2-Cl-	71	1:05
	H-fPRPGGGGNGDFEEIPEEYL-OH		Trt
4	Angiotensin (SEQ ID NO: 4)	Vasoconstrictor	Cl-2-Cl-	82	0:30
	H-NRVYVHPF-OH		Trt
5	PTH 1-34 (SEQ ID NO: 5)	Osteoporosis	RA	70	1:43
	H-SVSEIQLMHNLGKHLNSMERVEWLRKKLQDVHNF-		ProTide
	NH2
6	Gonadorelin (SEQ ID NO: 6)	Fertility	RA	91	0:35
	pEHWSYGLRPG-NH2		ProTide
7	Triptorelin (SEQ ID NO: 7)	Breast Cancer,	RA	73	0:35
	pEHWSYwLRPG-NH2	Prostrate	ProTide
		Cancer,
8	Liraglutide (SEQ ID NO: 8)	Diabetes	RA	80	1:31
	H-HAEGTFTSDVSSYLEGQAAK(Y-E-		ProTide
	palmitoyl)EFIAWLVRGRG-NH2
9	Exenatide (SEQ ID NO: 9)	Diabetes	RA	74	1:58
	H-		ProTide
	HGEGTFTSDLSKQMEEEAVRLFIEWLKNGGPSSGAPPPS-
	NH2
10	MOG (35-55) (SEQ ID NO: 10)	Multiple	RA	71	1:05
	H-MEVGWYRSPFSRVVHLYRNGK-NH2	Sclerosis	ProTide
11	Secretin (SEQ ID NO: 11)	Osmoregulation	RA	70	1:19
	H-HDGTFTSELSRLRDSARLQRLLQGLV-NH2		ProTide
12	Teriparatide (SEQ ID NO: 12)	Osteoporosis	RA	60	1:43
	H-SVSEIQLMHNLGKHLNSMERVEWLRKKLQDVHNF-		ProTide
	NH2
13	GLP-1 (7-37) (SEQ ID NO: 13)	Diabetes	RA	74	1:34
	H-HAEGTFTSDVSSYLEGQAAKEFIAWLVKGRG-NH2		ProTide
14	Magainin 1 (SEQ ID NO: 14)	Antibiotic	RA	79	1:11
	H-GIGKFLHSAGKFGKAFVGEIMKS-NH2		ProTide
15	Tetracosactide (SEQ ID NO: 15)	Adrenal Cortex	RA	77	1:13
	H-SYSMEHFRWGKPVGKKRRPVKVYP-NH2	stimulant	ProTide
16	[Arg8]-Vasopressin (SEQ ID NO: 16)	Hormone (blood	RA	94	0:32
	H-CYFQNCPRG-NH2	vessel	ProTide
17	Ubiquitin (SEQ ID NO: 17)	Protein	RA	≥60	3:44
	MQIFVKTLTGKTITLEVEPSDTIENVKAKIQDKEGIPPDQ	signaling agent	ProTide
	QRLIFAGKQLEDGRTLSDYNIQKESTLHLVLRLRGG-NH2
18	Parasin I (SEQ ID NO: 18)	Antibiotic	RA	87	0:59
	H-KGRGKQGGKVRAKAKTRSS-NH2		ProTide
19	Dynorphin A (SEQ ID NO: 19)	Opioid	RA	71	0:53
	H-YGGFLRRIRPKLKWDNQ-NH2	Research	ProTide
20	ACP (SEQ ID NO: 20)	Fatty Acid	RA	92	0:32
	H-VQAAIDYING-NH2	Synthesis	ProTide
21	BAM 3200 (SEQ ID NO: 21)	Opioid	RA	70	1:16
	H-YGGFMRRVGRPEWWMDYQKRYGGFL-NH2	Research	ProTide
22	HIV-TAT  (47-57) (SEQ ID NO: 22)	HIV/AIDS	RA	93	0:31
	Fmoc-YGRKKRRQRRR-NH2	Research	ProTide
23	HIV-TAT (48-60) (SEQ ID NO: 23)	HIV/AIDS	RA	88	0:39
	Fmoc-GRKKRRQRRRPPQ-NH2	Research	ProTide
24	Pramlintide (SEQ ID NO: 24)	Diabetes	RA	72	1:52
	KCNTATCATQRLANFLVHSSNNFGPILPPTNVGSNTY--		ProTide
	NH2

All peptides synthesized in Table 1 gave the desired target as the major peak with a standard cycle time of 2 minutes and 58 seconds. The in-situ solvent recycling process allowed for 0.5 mL of a concentrated pyrrolidine (BP 87° C.) solution to be added to the end of the coupling step (without draining). An advantage of this setup was that the deprotection immediately proceeded very close to the desired temperature (95° C.) because the coupling solution was already at 90° C. During the deprotection process a vacuum was applied and the pyrrolidine was evaporated and subsequently condensed in the waste container. This allowed only a single wash step (1×4 mL) to be required at the end of the deprotection step.

Total synthesis time for entire batch: 32.6 hours

This new process provided a significant reduction in standard cycle time (2 minutes 57 seconds) from (a)—elimination of the coupling drain time, (b)—elimination of the deprotection delivery time between steps, and (c)—elimination of the temperature ramp time for the deprotection step thereby allowing a shorter deprotection time to be used. Additionally, significant solvent savings were possible with the complete elimination of the deprotection solvent during each cycle.

In the drawings and specification there has been set forth a preferred embodiment of the invention, and although specific terms have been employed, they are used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention being defined in the claims.

Claims

1. A method of deprotection in batch solid phase peptide synthesis in which the improvement comprises: adding a base deprotection composition to a mixture of a coupling solution, a growing peptide chain, and any excess activated amino acid from a preceding coupling step;wherein the deprotection composition has a concentration of at least 50% base by volume and is added to the mixture of the coupling solution, the growing peptide chain, and any excess activated amino acid from the preceding coupling step in an amount that is less than ⅓ of the volume of the coupling solution;without any draining step between the coupling step of the preceding coupling cycle and the addition of the deprotection composition for the successive cycle; andwith the coupling solution at least 30° C.

2. A method according to claim 1 wherein the deprotection composition is an organic base.

3. A method according to claim 1 using Fmoc solid phase peptide chemistry.

4. A method of deprotection in batch solid phase peptide synthesis in which the improvement comprises: adding a base deprotection composition to a mixture of a coupling solution, a growing peptide chain, and any excess activated amino acid from the preceding coupling cycle step;wherein the deprotection composition is added to the mixture of the coupling solution, the growing peptide chain, and any excess activated amino acid from the preceding coupling step in a concentration of at least 50% base by volume and an amount that is less than ⅓ of the volume of the coupling solution;without any draining step between the coupling step of the preceding coupling cycle and the addition of the deprotection composition for the successive cycle which removes at least 50% of the volume of the preceding coupling cycle coupling solution; andwith the coupling solution at a temperature of at least 30° C.

5. A method according to claim 4 wherein the deprotection composition is an organic base.

6. A method according to claim 4 using Fmoc solid phase peptide chemistry.