SYNTHESIS OF CALEBIN-A AND ITS BIOLOGICALLY ACTIVE ANALOGS

Abstract

Disclosed is a simple, economical, industrially scalable green synthetic process for Calebin-A and its biologically active analogs.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention in general relates to calebinoids. More specifically, the present invention relates to a simple, economical and scalable green process for the synthesis of Calebin A and its biologically active analogs.

2. Description of Prior Art

Darrick S. H. L. Kim and So-Young Park isolated and identified Calebin-A from Curcuma longa in 2001 (Park S. Y. & Kim, D. S. H. L., J. Nat. Prod., 2002, 65, 1227-1231). Demethoxycalebin-Al and demethoxycalebin-A2 have been isolated as a pair from Curcuma longa by Feng Qiu et al. in 2007 (Zeng, Y. C., Qiu, F., Takahashi, K., Liang, J. M., Qu, G. X. & Yao, X. S., Chem. Pharm. Bull., 2007, 55, 940-943). By analogy, bisdemethoxycalebin-A may also be present in Curcuma longa though not reported yet. Darrick S. H. L. Kim and Jin Y. Kim synthesized Calebin-A and some of its analogs through a circuitous route (five steps) starting from 1-hydroxyacetone (1) (Kim, D. S. H. L. & Kim, J. Y., Bioorg. Med. Chem. Lett., 2001, 11, 2541-2543). The calebinoids having free p-hydroxy group are biologically active. Subsequently D. H. S. L. Kim has patented the pharmaceutical compositions of Calebin-A and its analogs as useful for prevention and treatment of β-amyloid peptide-induced disease [U.S. Pat. No. 7,572,829 B2 (2009). This synthesis has been represented as FIGURE-Prior Art. In short, this prior art synthetic scheme involves protection of 1-hydroxyacetone (1) and vanillin (4) as their tetrahydropyranyl (THP) ethers (2 & 5) using dihydropyran. THP ether of 1-hydroxyacetone (2) is treated with Lithium diisopropylamide (LDA) at low temperature (−78° C.) to generate the lithio anion at the α-methyl of the keto group. This lithio anion adds to the aldehyde group of the THP ether of vanillin (5) to give the β-hydroxy-ketone (3). This is dehydrated and deprotected to Feruloylmethanol (6) which is coupled to ferulic acid (7) in the presence of 4-dimethylaminopyridine (DMAP), DMAP-HCl and N,N-Dicyclohexylcarbodiimide (DCC) to get Calebin-A (10a). The synthetic scheme for Calebin-A discussed herein above is the only known for Calebin-A and its analogs. However, it suffers from the following technical disadvantages.

• • 1. The starting material 1-hydroxyacetone is expensive.
  • 2. The condensation of vanillin with 1-hydroxyacetone involves protection of the hydroxyls as their THP ethers to avoid Lithium diisopropylamide reacting with hydroxyls.
  • 3. 4-dimethylaminopyridine and N, N-Dicyclohexyl carbodiimide are also expensive.
  • 4. The synthesis involves a minimum of five steps, very low temperature (−78° C.), pyrophoric and moisture sensitive reagents.

All aforesaid factors make this process industrially non-feasible for scale up.

It is therefore the principle objective of the present invention to describe a simple, economical, scalable green process for the synthesis of Calebin-A and its analogs.

The present invention fulfills the principle objective and provides further related advantages.

SUMMARY OF THE INVENTION

The present invention discloses a simple, economical, green and industrially scalable synthetic process for Calebin-A and its biologically active analogs. The disclosed invention has the following advantages. They are,

• • 1. It is a single step synthetic scheme;
  • 2. Economic viability is achieved in terms of low costs of the synthetic process;
  • 3. It is an example of green process that is environmental friendly; and
  • 4. The synthetic scheme assures industrial scalability.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGURE-Prior Art shows the prior art synthetic scheme for Calebin A

DESCRIPTION OF THE MOST PREFERRED EMBODIMENT

In the most preferred embodiment, the present invention relates to a general synthetic process for the compound represented by general STR#3 wherein the dotted configuration . . . is optionally single bond or double bond; R₁ is selected from the group consisting of OH, OMe, OR_a and X wherein R_a is alkyl, alkenyl, or alkynyl and X is F, Cl, Br, or I; R₂ is selected from group consisting of H, OMe, and OR_a wherein R_a is alkyl, alkenyl, or alkynyl; R₃ is selected from the group consisting of OH, OMe, OR_a and X where R_a is alkyl, alkenyl, or alkynyl and X is F, Cl, Br, or I; R₄ is selected from group consisting of H, OMe, and OR_a where R_a is alkyl, alkenyl, or alkynyl; and wherein both dotted lines are double bonds and R₁ is OH, R₂ is OMe, R₃ is OH and R₄ is H, said synthetic process comprising the steps of

• • A. Mixing the iodomethyl ketone of general structure STR#1 having substituents R₁ and R₂ as defined vide supra, as dissolved in a solvent with the aqueous solution of the sodium or potassium salt of the acid of general structure (STR#2) [1.0-4.0] mole equivalent, where M=Na⁺ or K⁺ and R₃ and R₄ as defined vide supra;

• • B. Stirring the mixture of Step A at ambient temperature (5° C.-30° C.) in the presence of a phase transfer catalyst (5-10 mole percent with respect to the iodide) and stirring the mixture for 24-72 hours;
  • C. Separating the organic layer from the product of Step B, washing with aqueous sodium hydrogen carbonate solution followed by drying over anhydrous sodium sulfate, filtering and stripping off the solvent under vacuum followed by crystallization of the crude from ethyl acetate or ethanol to get compound represented by general structure STR#3.

In another most preferred embodiment, the present invention relates to a simple, economical, industrially scalable green synthetic scheme for Calebin-A and its demethoxy analogs as represented herein below.

Specifically, the present invention relates to a general synthetic process for Calebin-A (Feruloylmethyl ferulate-10a) and its demethoxy analogs (Feruloylmethyl 4-hydroxycinnamate-10b, 4-Hydroxycinnamoylmethyl ferulate-10c and 4-Hydroxycinnamoylmethyl 4-hydroxycinnamate-10d), said process comprising the steps of:

• • A. Mixing feruloyl or 4-hydroxycinnamoyliodomethane (8a or 8b, 0.015 mol) dissolved in a solvent with the aqueous solution of sodium or potassium salt of ferulic acid or 4-hydroxycinnamic acid ((9a or 9b), 1.0-4.0 mole equivalent);
  • B. Stirring the mixture of Step A at ambient temperature (5° C.-30° C.) in the presence of a phase transfer catalyst (5-10 mole percent with respect to the iodide) and stirring the mixture for 24-72 hours;
  • C. Separating the organic layer from the product of Step B, washing with aqueous sodium hydrogen carbonate solution followed by drying over anhydrous sodium sulfate, filtering and stripping off the solvent under vacuum followed by crystallization of the crude from ethyl acetate or ethanol to get Calebin-A (Feruloylmethyl ferulate-10a) or its demethoxy analogs (Feruloylmethyl 4-hydroxycinnamate-10b, 4-Hydroxycinnamoylmethyl ferulate-10c and 4-Hydroxycinnamoylmethyl 4-hydroxycinnamate-10d) as pale yellow crystalline solids in 50-60% yield.

In specific embodiments, the ideal solvent for dissolving Feruloyl or 4-hydroxycinnamoyliodomethane as mentioned herein above is one selected from group comprising dichloromethane, chloroform, ethyl acetate and tetrahydrofuran among others.

In further specific embodiments, ideal phase transfer catalysts used in aforementioned synthetic scheme is one selected from group comprising tetrabutylammonium bromide, tetrabutylammonium hydrogensulfate, benzyltributyl ammonium chloride, benzyltriethylammonium chloride and benzyltrimethyl ammonium chloride among others.

Specific examples of the general synthetic scheme for Calebin A and its demethoxy analogs discussed herein above are provided in the following paragraphs. Feruloyliodomethane and 4-Hydroxycinnamoyliodomethane used in examples included herein below were prepared according to a reported method (Wang, Z., Yin, G., Qin, J., Gao, M., Cao, L & Wu, A., Synthesis, 2008, 22, 3675-3681).

Example 1

Calebin-A (Feruloylmethyl Ferulate, 10a)

Calebin-A (10a) was prepared by reacting feruloyliodomethane with sodium or potassium salt of ferulic acid with reaction steps and conditions maintained as mentioned in the general synthetic scheme discussed herein above in Para 0010. The yield of the product was 60%.

Calebin-A (Feruloylmethyl ferulate, 10a): Pale yellow solid; m.p. 138-140° C.; ¹H NMR (Acetone-d6, 300 MHz): δ 3.902 (s, 3H), 3.929 (s, 3H), 5.106 (s, 2H), 6.518 (d, J=15.9 Hz, 1H), 6.856 (d, J=16.2 Hz, 1H), 6.886 (d, J=8.4 Hz, 1H), 6.892 (d, J=8.4 Hz, 1H), 7.180 (dd, J=8.4 Hz, 1.8 Hz, 1H), 7.214 (dd, J=8.4 Hz, 1.8 Hz, 1H), 7.375 (d, J=1.8 Hz, 1H), 7.386 (d, J=1.8 Hz, 1H), 7.666 (d, J=16.2 Hz, 1H), 7.671 (d, J=15.9 Hz, 1H), 8.246 (s, 1H), 8.309 (s, 1H).

¹³C NMR (Acetone-d6, 75 MHz): δ 56.267, 56.296, 67.927, 111.290. 111.524, 116.077, 116.201, 120.322, 124.165, 124.494, 127.349, 127.408, 144.389, 146.505, 148.752, 150.209, 150.501, 166.898, 192.963.

LC-MS (+APCI): m/z 385 (M⁺+1); LC-MS (−APCI): m/z 383 (M⁺−1).

Example 2

Demethoxycalebin-A1 (Feruloylmethyl 4-Hydroxycinnamate 10b)

Demethoxycalebin-A1 (Feruloylmethyl 4-hydroxycinnamate 10b) was prepared by reacting feruloyliodomethane with sodium or potassium salt of 4-hydroxycinnamic acid with reaction steps and conditions maintained as mentioned in the general synthetic scheme discussed herein above in Para 0010. The yield of the product was 50%.

Demethoxycalebin-A1 (Feruloylmethyl 4-hydroxycinnamate, 10b): Pale yellow solid; m.p. 181.4-183.4° C.;

¹H NMR (DMSO-d6, 300 MHz): δ 3.815 (s, 3H), 5.132 (s, 2H), 6.508 (d, J=16.2 Hz, 1H), 6.813 (d, J=8.4 Hz, 2H), 6.825 (d, J=8.4 Hz, 1H), 6.842 (d, J=16.8 Hz, 1H), 7.173 (dd, J=8.4 Hz, 1.5 Hz, 1H), 7.336 (d, J=1.5 Hz, 1H), 7.592 (d, J=8.4 Hz, 2H), 7.623 (d, J=16.8 Hz, 1H), 7.626 (d, J=16.2 Hz, 1H), 9.814 (s, 1H), 10.135 (s, 1H).

¹³C NMR (DMSO-d6, 75 MHz): δ 55.764, 55.793, 67.263, 111.431, 113.656, 115.778, 115.961, 119.541, 123.837, 125.162, 125.763, 130.637, 143.959, 145.643, 148.110, 149.925, 160.121, 166.189, 192.753.

LC-MS (+APCI): m/z 355 (M⁺+1); LC-MS (−APCI): m/z 353 (M⁺−1).

Example 3

Demethoxycalebin-A2 (4-Hydroxycinnamoylmethyl Ferulate 10c)

Demethoxycalebin-A2 (4-Hydroxycinnamoylmethyl ferulate 10c) was prepared by reacting 4-hydroxycinnamoyliodomethane with sodium or potassium salt of ferulic acid with reaction steps and conditions maintained as mentioned in the general synthetic scheme discussed herein above in Para 0010. The yield of the product was 50%.

Demethoxycalebin-A2 (4-Hydroxycinnamoylmethyl ferulate, 10c): Cremish solid, m.p. 175.7-177.7° C.

¹H NMR (DMSO-d₆, 300 MHz): δ 3.819 (s, 3H), 5.127 (s, 2H), 6.591 (d, J=16.2 Hz, 1H), 6.773 (d, J=16.2 Hz, 1H), 6.807 (d, J=8.4 Hz, 1H), 6.825 (d, J=8.4 Hz, 2H), 7.157 (dd, J=8.4 Hz, 1.8 Hz, 1H), 7.357 (d, J=1.8 Hz, 1H), 7.589 (d, J=8.4 Hz, 2H), 7.614 (d, J=16.2 Hz, 1H), 7.631 (d, J=16.2 Hz, 1H), 9.731 (s, 1H), 10.207 (s, 1H).

¹³C NMR (DMSO-d₆, 75 MHz): δ 55.786, 55.815, 67.249, 111.372, 113.934, 115.632, 116.042, 119.211, 123.450, 125.236, 125.631, 130.835, 143.601, 145.936, 148.058, 149.596, 160.370, 166.197, 192.775.

LC-MS (+APCI): m/z 355 (M⁺+1); LC-MS (−APCI): m/z 353 (M⁺−1).

Example 4

Bisdemethoxycalebin-A (4-Hydroxycinnamoylmethyl 4-hydroxycinnamate, 10d)

Bis-demethoxycalebin-A (4-Hydroxycinnamoylmethyl 4-hydroxycinnamate, 10d) was prepared by reacting 4-hydroxycinnamoyliodomethane with sodium or potassium salt of 4-hydroxycinnamic acid with reaction steps and conditions maintained as mentioned in the general synthetic scheme discussed herein above in Para 0010. The yield of the product was 55%.

Bisdemethoxycalebin-A (4-Hydroxycinnamoylmethyl 4-hydroxycinnamate, 10d): Pale yellow solid: m.p. 289-291° C.;

¹H NMR (DMSO-d₆, 300 MHz): δ 5.120 (s, 2H), 6.507 (d, J=15.9 Hz, 1H), 6.771 (d, J=15.9 Hz, 1H), 6.813 (d, J=8.4 Hz, 2H), 6.825 (d, J=8.4 Hz, 2H), 7.587 (d, J=8.4 Hz, 4H), 7.626 (d, J=15.9 Hz, 2H), 10.140 (s, 1H), 10.201 (s, 1H).

¹³C NMR (DMSO-d₆, 75 MHz): δ 67.293, 113.648, 115.976, 116.086, 119.219, 125.177, 125.265, 130.645, 130.879, 143.645, 145.658, 160.136, 160.407, 166.204, 192.819.

LC-MS (+APCI): m/z 325 (M⁺+1); LC-MS (−APCI): m/z 323 (M⁺−1).

The examples included herein substantiate the most preferred embodiment of the invention. These examples should not be construed to limit the scope of variations possible in the practice of the instant invention. The examples are thus illustrative and not exhaustive.

Claims

1. A general synthetic process for the compound represented by general STR#3 wherein the dotted configuration . . . is optionally single bond or double bond; R1 is selected from the group consisting of OH, OMe, ORa and X wherein Ra is alkyl, alkenyl, or alkynyl and X is F, Cl, Br, or I; R2 is selected from group consisting of H, OMe, and ORa wherein Ra is alkyl, alkenyl, or alkynyl; R3 is selected from the group consisting of OH, OMe, ORa and X where Ra is alkyl, alkenyl, or alkynyl and X is F, Cl, Br, or I; R4 is selected from group consisting of H, OMe, and ORa where Ra is alkyl, alkenyl, or alkynyl; and wherein both dotted lines are double bonds and R1 is OH, R2 is OMe, R3 is OH and R4 is H, said synthetic process comprising the steps of A. Mixing the iodomethyl ketone of general structure STR#1 having substituents R1 and R2 as defined vide supra, as dissolved in a solvent with the aqueous solution of the sodium or potassium salt of the acid of general structure (STR#2) [1.0-4.0] mole equivalent, where M=Na+ or K+ and R3 and R4 as defined vide supra;

2. A general synthetic process for Calebin-A (Feruloylmethyl ferulate) or its demethoxy analogs (Feruloylmethyl 4-hydroxycinnamate, 4-Hydroxycinnamoylmethyl ferulate and 4-Hydroxycinnamoylmethyl 4-hydroxycinnamate), said process comprising the steps of: A. Mixing feruloyl or 4-hydroxycinnamoyliodomethane (0.015 mol) dissolved in a solvent with the aqueous solution of sodium or potassium salt of ferulic acid or 4-hydroxycinnamic acid (1.0-4.0 mole equivalent);B. Stirring the mixture of Step A at ambient temperature (5° C.-30° C.) in the presence of a phase transfer catalyst (5-10 mole percent with respect to the iodide) and stirring the mixture for 24-72 hours;C. Separating the organic layer from the product of Step B, washing with aqueous sodium hydrogen carbonate solution followed by drying over anhydrous sodium sulfate, filtering and stripping off the solvent under vacuum followed by crystallization of the crude from ethyl acetate or ethanol to get Calebin-A (Feruloylmethyl ferulate) or its demethoxy analogs (Feruloylmethyl 4-hydroxycinnamate, 4-Hydroxycinnamoylmethyl ferulate and 4-Hydroxycinnamoylmethyl 4-hydroxycinnamate) as pale yellow crystalline solids in 50-60% yield.

3. The process according to claim 2 wherein synthesis of Calebin-A (Feruloylmethyl ferulate) involves reacting feruloyliodomethane with sodium or potassium salt of ferulic acid in step A.

4. The process according to claim 2 wherein synthesis of Feruloylmethyl 4-hydroxycinnamate involves reacting feruloyliodomethane with sodium or potassium salt of 4-hydroxycinnamic acid in step A.

5. The process according to claim 2 wherein synthesis of 4-Hydroxycinnamoylmethyl ferulate involves reacting 4-hydroxycinnamoyliodomethane with sodium or potassium salt of ferulic acid in step A.

6. The process according to claim 2 wherein synthesis of 4-Hydroxycinnamoylmethyl 4-hydroxycinnamate involves reacting 4-hydroxycinnamoyliodomethane with sodium or potassium salt of 4-hydroxycinnamic acid in step A.

7. The process according to claims 1 and 2 wherein the solvent used in step A is one selected from group comprising dichloromethane, chloroform, ethyl acetate and tetrahydrofuran.

8. The process according to claims 1 and 2 wherein the phase transfer catalyst used in step B is one selected from group comprising tetrabutylammonium bromide, tetrabutylammonium hydrogensulfate, benzyltributyl ammonium chloride, benzyltriethylammonium chloride and benzyltrimethyl ammonium chloride.