WO1995011893A1

WO1995011893A1 - Compounds and methods for synthesizing pantethine, pantetheine and derivatives thereof

Info

Publication number: WO1995011893A1
Application number: PCT/US1994/012374
Authority: WO
Inventors: Ghanshyam Patil
Original assignee: Oculon Corporation
Priority date: 1993-10-27
Filing date: 1994-10-26
Publication date: 1995-05-04
Also published as: AU1128295A

Abstract

There is disclosed compounds and methods for the synthesis of pantethine, pantetheine, and derivatives thereof. The methods utilize crystalline derivatives of the above compounds as intermediates which readily permit purification by recrystallization, and thus allow the generation of highly pure products. The synthesis utilizes the 1,3-diol functional group present in pantothenic acid to produce the crystalline derivatives by formation of ketal intermediates. Subsequent hydrolisis of the ketal intermediates yields pantethine or pantetheine in highly pure form.

Description

COMPOUNDS AND METHODS FOR SYNTHESIZING PANTETHINE,

PANTETHEINE AND DERIVATIVES THEREOF

Technical Field

This invention relates generally to compounds and methods for synthesizing pantethine, pantetheine and derivatives thereof, and more specifically, to methods of synthesizing pantethine, pantetheine and derivatives thereof utilizing recrystallizable ketal intermediates.

Background of the Invention

Pantethine and pantetheine are known compounds having numerous utility, including use as therapeutic agents to treat a variety o: disease states. Existing methods of synthesizing these compounds employ the reaction between an active ester of pantothenic acid and cystamine or cysteamine to yield pantethine and pantetheine, respectively. Due to the water solubility of the above materials, extensive cleanup is involved in order to obtain pure pantethine and pantetheine by the above reaction. Specifically, ion-exchange chromatography, or some other purification technique, is required. Such techniques, however, are impractical for large scale synthesis, and have further associated disadvangtages, including the need for large volumes of water.

Although high yields and relatively high purity of pantethine and pantetheine have been reported in the literature, a large scale synthesis method of manufacturing pantethine and pantetheine in high yield and purity is still desired. In addition, there is a need in the art for the synthesis and isolation of stable chemical intermediates which may be readily converted to pantethine and pantetheine. Moreover, there is also a need for synthesis techniques which may readily yield derivatives of pantethine and pantetheine which have thereapuetic utility and/or which may serve as prσdrugs to pantethine and pantetheine.

The present invention fulfills these needs and provides further related advantages.

Summary of the Invention

In brief, this invention is directed to compounds and methods for synthesizing pantethine, pantetheine and derivatives thereof. The methods utilize recrystallizable ketal intermediates which results in the production of highly pure pantethine, pantetheine and derivatives thereof.

In one embodiment, the invention discloses a method of synthesizing a pantothenic acid ketal by reacting pantothenic acid (or a salt thereof) with a ketone and an acid, and obtaining the resulting ketal by crystallization. In a preferred embodiment, the ketone is acetone and the resulting compound is 1,3-isopropylidene-D-pantothenic acid.

In another embodiment, the pantothenic acid ketal is further reacted with either cystamine or cysteamine (or salts thereof) to yield a pantethine ketal or pantetheine ketal, respectively. In a preferred embodiment, the ketals of pantethine and pantetheine are 1,3-isopropylidene-D-pantethine and 1,3-isopropylidene-D-pantetheine, respectively. In a related embodiment, the pantethine and pantetheine ketals are hydrolyzed to yield pantethine and pantetheine, respectively.

In a further embodiment, the pantetheine ketal is reacted with an esterifying agent, thus modifying the terminal sulfhydryl moiety. Such modifications include reaction with esterifying agents to yield pantetheine ketal thioesters. Such thioesters may be hydrolyzed to yield the corresponding pantetheine thioesters. In yet another embodiment, novel compounds are disclosed, including pantothenic acid ketals, pantethine ketals, pantetheine ketals, pantetheine ketal thioesters and pantetheine thioesters.

Other aspects of this invention will become apparent upon reference to the following detailed description.

Detailed Description

The present invention is generally directed to compounds and methods for synthesizing pantethine, pantetheine and derivatives thereof. The methods of this invention utilize synthetic intermediates which are readily purified, and therefore result in the production of pantethine and pantetheine in high purity (as used herein, high purity means purity in excess of 90%, preferably in excess of 95%, more preferably in excess of 98%, and most preferably in excess of 99%). The synthetic methods of the present invention are also applicable to compounds structurally related to pantethine and pantetheine (referred to herein as "derivatives" of pantethine and pantetheine).

Pantethine and pantetheine have utility for existing uses of these compounds, including (but not limited to) use as anti-cataract agents as disclosed in U.S. Patent No. 5.091,421 (hereby incorporated by reference in its entirety). Moreover, the derivatives of pantethine and pantetheine disclosed herein also possess utility as anti- cataract agents, and may further serve as prodrugs to pantethine and pantetheine. As used herein, a prodrug is a compound which is converted in vivo to an active biological agent, such as pantethine and pantetheine. The ability of the derivatives of pantethine and pantetheine to serve as anti-cataract agents and/or prodrugs is disclosed in U.S. Patent Application Serial No. (awaiting serial number), filed October 27, 1993, entitled "Compounds and Methods for Inhibiting Cataract Formation" (which application is hereby incorporated by reference in its entirety).

In one embodiment of the present invention, pantethine is synthesized in high purity by the following steps: (1) forming a ketal of pantothenic acid , (2) coupling cystamine to the pantothenic acid ketal to provide a pantethine ketal, and (3) hydrolyzing the pantethine ketal to yield pantethine. Purification of the ketal synthetic intermediates by recrystallization affords highly pure pantethine.

The synthetic method of the present invention also affords highly pure pantetheine. In this embodiment, pantetheine is synthesized according to the following steps: (1) forming a ketal of pantothenic acid, (2) coupling cysteamine to the pantothenic acid ketal to provide a pantetheine ketal, and (3) hydrolyzing the pantetheine ketal to yield pantetheine. Again, purification of the ketal synthetic intermediates by recrystallization yields highly pure pantetheine.

In a further embodiment, the method of the present invention also provides highly pure pantethine and pantetheine derivatives, including S-substituted pantetheine derivatives (pantetheine thioesters). The method of synthesis of pantetheine thioesters comprises the steps of (1) forming a ketal of pantothenic acid, (2) coupling cysteamine to the pantothenic acid ketal to provide a pantetheine ketal, (3) reacting the sulfhydryl group of the pantetheine ketal with an esterifying agent to produce a pantetheine ketal thioester, and (4) hydrolyzing the pantetheine ketal thioester to yield a pantetheine thioester.

The methods of synthesis of pantethine, pantetheine, and derivatives thereof are based upon the intermediacy of crystalline ketal derivatives of these species. Because these ketals are crystalline, these compounds may be readily purified by recrystallization, and thus obtained in highly pure form. Accordingly, subsequent deketalization of these highly pure ketal derivatives by mild aqueous hydrolysis affords pantethine, pantetheine, and derivatives thereof in highly pure form.

In brief, the method of the present invention utilizes the 1,3-diol functional group present in pantothenic acid as the site of chemical elaboration to produce ketal derivatives which may be readily purified by recrystallization. Thus, pantothenic acid serves as the starting point for the chemical synthesis of pantethine, pantetheine, and derivatives thereof. The crystalline ketal intermediates may be subjected to recrystallization, as necessary, to afford ketals of high purity (e.g., 99% or greater). Ketal purity may be ascertained by any one of a variety of techniques, including melting point determination, as well as spectrographic or chromatographic analysis. Once the requisite purity is attained, hydrolysis of the ketal regenerates the 1,3-diol functional group of pantethine, pantetheine, or derivatives thereof in highly pure form.

In one embodiment of the present invention, a method for the ketalization of pantothenic acid is disclosed. In this method, sodium pantothenate (Aldrich Chemical Co., Milwaukee, WI) is treated with acetone under acidic conditions to yield the acetone ketal of pantothenic aid, 1, 3-isopropylidene pantothenic acid. More specifically, a solution of sodium pantothenate in acetone may be treated with either a catalytic or stoichiometric amount of an acid such as sulfuric acid and heated at reflux for several hours to effect conversion of the diol to the corresponding ketal. The ketal may be then be isolated by crystallization by dilution of the solution with a nonpolar solvent such as hexane. The crystallized ketal may be collected by filtration, washed with an appropriate solvent, and recrystailized as necessary to afford the purified ketal synthetic intermediate. The formation of the acetone ketal of pantothenic acid by the process described above may be referred to as direct ketalization.

Alternatively, pantothenic acid may be treated with a ketal of acetone such as 2,2-dimethoxypropane (acetone dimethyl ketal) under acidic reaction conditions, to provide the acetone ketal of pantothenic acid by a process referred to as trans-ketalization. In this process, the acetone ketal is exchanged or transferred from the ketalizing reagent, 2,2-dimethoxypropane, to pantothenic acid. Specifically, a solution of sodium pantothenate in acetone may be treated with a single molar equivalent of sulfuric acid followed by treatment with 2,2-dimethoxypropane. After heating the reaction mixture for for several hours to complete ketal formation, the crude product may be isolated by an aqueous extractive process utilizing methylene chloride and water. The ketal thus obtained may be recrystallized from a suitable solvent system such as acetone-hexane (1:1) to provide highly pure 1,3-isopropylidene-D-pantothenic acid. A representative experimental procedure for the formation of the acetone ketal of pantothenic acid is described in detail in Example 1. The acetone ketal of pantothenic acid, 1,3-isopropylidene-D-pantothenic acid, may be represented by formula I:

In a preferred embodiment, the pantothenic acid ketal is the acetone ketal of structure I. However, other pantothenic acid ketals may be utilized which are derived from a variety of kenones (which may be represented generally as "R₁-C (=O) -R₂"). Suitable ketones are those which provide pantothenic acid ketals which are crystalline and capable of recrystallization to provide highly pure ketals (e.g., 99% or greater). Preferred ketones include dialkyl ketones containing from four to eight carbons, such as methyl ethyl ketone (2-butanone); cyclic ketones containing from three to seven carbon atoms, such as cyclopentanone and cyclohexanone; alkyl aryl ketones, such as methyl phenyl ketone (acetophenone); and diaryl ketones, such as diphenyl ketone

(benzophenone). The pantothenic acid ketals derived from the above-mentioned ketones may be generally represented by formula I':

wherein R₁ and R₂ individually represent alkyl groups of a dialkyl ketone, alkyl and aryl groups of an alkyl aryl ketone, and aryl groups of a diaryl ketone as disclosed above, or wherein R₁ and R₂ taken together represent the carbocyle of a cyclic ketone as disclosed above. More specifically, suitable alkyl groups include saturated and unsaturated, branched or unbranched, substituted or unsubstituted C₁ to C₁₀ alkyl moieties and C₃ to C₁₀ cycloalkyl moieties. Suitable aryl groups include C₆ to C₁₀ aryl moieties.

In the method of this invention, ketal formation may ocvir under acidic conditions. Suitable acids for these conditions include organic acids and mineral acids. Organic acids include carboxylic acids, ammonium salts, sulfinic acids, and sulfonic acids. Mineral acids include hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid. In a preferred embodiment, ketal formation utilizes sulfuric acid.

In another embodiment of the method of the present invention, the coupling of either cystamine or cysteamine to the ketal of pantothenic acid is performed. In this embodiment, the amino group of either cystamine or cysteamine is coupled to the carboxy group of the pantothenic acid ketal to form an amide bond to produce the ketal of pantethine or pantetheine, respectively. This coupling reaction may optionally utilize a coupling agent to effect amide bond formation. Such coupling agents include those reagents which activate carboxylic acid groups toward nucleophilic substitution. Suitable reagents include thionyl chloride (which transforms carboxylic acids to acid chlorides), various chloroformates (which convert carboxylic acids into reactive anhydrides), and diimide reagents such as dicyclohexyl carbodiimide (DCC) and 1-(3-dimethylaminopropyl)-3-ethyl carbodiimide (EDO (which convert carboxylic acids to active ester derivatives). In the practice of this invention, a preferred coupling agent is carbonyl diimidazole (CDI) which converts carboxylic acids to carbonyl imidazoles.

Alternatively, the coupling of cystamine or cysteamine to the ketal of pantothenic acid may be accomplished by esterifying the ketal by refluxing in methanol with a catalytic amount of concentrated sulfuric acid. To this crude reaction mixture is added cysteamine (1 equivalent) or cysteamine (0.5 equivalents), and refluxed for an additional period of time. The mixture is then evaporated to dryness, redissolved in methylene chloride and washed with dilute HCl, saturated NaHCO₃ and brine, and then dried (MgSO₄), filtered and evaporated to dryness. More generally, the pantothenic acid ketal (i.e., structure I above) is coupled with cystamine to yield the pantethine ketal of structure II, or is coupled with cysteamine to yield the pantetheine ketal of structure III. The coupling of cystamine or cysteamine to a representative pantothenic acid ketal (i.e., 1,3-isopropylidene-D-pantothenic acid) utilizing carbonyl diimidazole to produce the 1,3-isopropylidenes of pantethine and pantetheine are described in detail in Examples 2 and 4, respectively. In general, these coupling reactions may be represented schematically as follows:

The purity of the ketals of pantethine and pantetheine may be enhanced by recrystallization in a manner similar to that of the starting material, the pantothenic acid ketal. As mentioned above, the high purity of pantethine and pantetheine synthesized by the methods of the present invention is achieved by the high purity of the ketal intermediates (i.e., structures I', II and III above).

In a further embodiment of the present invention, pantethine is synthesized by hydrolysis of its corresponding ketal. Similarly, pantetheine may be synthesized by hydrolysis of its corresponding ketal. In these methods, the ketals are hydrolyzed to their corresponding 1,3-diols, pantethine and pantetheine, by treatment with aqueous acid. In a typical hydrolysis, the ketal is dissolved in 80% aqueous acetic acid and heated at S0°C for several hours. The hydrolysis product, a water soluble diol, may then be isolated by an aqueous extractive procedure using a methylene chloride and distilled water followed by lypholization. Suitable acids include organic acids and mineral acids. Organic acids include carboxylic acids (formic and acetic acid), ammonium salts, sulfinic acids, and sulfonic acids. Mineral acids include hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid. In a preferred embodiment, the ketal hydrolysis utilizes acetic acid. Representative hydrolyses of ketals II and III to pantethine and pantetheine, utilizing aqueous acetic acid, are described in detail in Examples 3 and 5, respectively. In general, the hydrolyses of these ketals is represented schematically below.

In yet another embodiment of the present invention, a method of esterifying the pantetheine ketal of structure III is disclosed. In this method, the sulfhydryl group of the pantetheine ketal is esterified with an esterifying agent to provide a pantetheine ketal thioester. As used herein, the term esterifying agent refers to any reactive acid derivative which is capable of reacting with a sulfhydryl group to form a thioester. A thioester may be thought of as resulting from the condensation of a sulfhydryl containing compound, a thiol, with an acid much in the same way that an ester results from the condensation of an alcohol with an acid. The pantetheine ketal thioesters produced by the methods of the present invention may be prepared from esterifying agents derived from carboxylic, carbamic, phosphoric, and sulfuric acid derivatives, and are represented by formula IV:

wherein R₁ and R₂ are as described above, and R₃ represents the residual portion of the esterifying agent.

The residual portion of the esterifying agent, R₃, is the portion of the esterifying agent which corresponds to the acid from which the esterifying group is derived, less the -OH group of the acid. For example, when the esterifying agent is a carboxylic acid derivative, such as an acid chloride, the residual portion of the esterifying agent corresponds to the carboxylic acid (i.e., R-CO₂H) from which the acid chloride is derived, less the OH group of the carboxylic acid (i.e., R₃ in this case would be -C(=O)R). Similarly, when the esterifying agent is a carbamic acid derivative, the residual portion of the esterifying agent corresponds to the carbamic acid (i.e., R₂N-CO₂H) less the OH group of the carboxylic acid (i.e., R₃ is -C (=O)NR₂). When the esterifying group is a phosphoric acid (H₃PO₄) or sulfuric acid (H₂SO₄) derivative, the residual portion of the esterifying group, R₃, is -PO₃H₂ and -SO₃H, respectively.

Esterifying agents derived from carboxylic acids include reactive carboxylic acid derivatives such as acid halides, carboxylic acid anhydrides, and reactive carboxylic ester derivatives, including p-nitrophenyl esters and N-hydroxysuccinimide esters. Suitable acid halide esterifying agents include acid chlorides such as acetyl chloride and benzyl chloride. The thioesters produced from carboxylic acid-derived esterifying agents by the methods of the present invention are represented by formula IVa:

wherein R₁ and R₂ as are as described above, and R represents the side chain of the carboxylic acid from which the esterifying agent is derived. Suitable R groups included hydrogen or saturated or unsaturated, branched or unbranched, substituted or unsubstituted C₁ to C₂₅ alkyl moieties, C₃ to C₂₅ cycloalkyl moieties, C₆ to C₂₅ aryl moieties, and combinations thereof. For example, C₁ to C₅ alkyl moieties include methyl, ethyl, propyl, isopropyl, butyl, sec-butyl, tert-butyl, pentyl, isopentyl, sec-pentyl and neopentyl; C₃ to C₆ cycloalkyl moeities include cyclopropyl, cyclobutyl, cyclopentyl and cyclohexyl; and C₆ and C₇ aryl moieties include phenyl, benzyl and tolyl. Substituted aryl moieties include substituted phenyl (such as p-acetylphenyl and p-acetimidylphenyl) and heteroaryl groups (such as furyl, thienyl and pyridyl). The synthesis of a representative pantetheine ketal thioester, S-trimethylacetyl-1,3-isopropylidene-D-pantetheine (i.e., structure IVa wherein R₁ = R₂ = CH₃ and R = 0(013)3), by esterification utilizing trimethylacetyl chloride is described in detail in Example 6.

Closely related to carboxylic acid esterifying groups are esterifying groups derived from carbamic acid. In the method of the present invention, these esterifying agents produce pantetheine ketal thioesters, which may also be referred to as pantetheine ketal thiocarbamates. The thioesters produced from carbamic acid-derived esterifying agents by the method of the present invention may be represented by formula IVb:

wherein R₁, R₂, and R are as described above.

The pantetheine ketal thioesters of the present invention derived from phosphoric and sulfuric acid derivatives may also be referred to as pantetheine ketal thiophosphonate and thiosulfonate esters, respectively. The thioesters produced from phosphoric and sulfuric acid-derived esterifying agents by the methods of the present invention are represented by formulas IVc and IVd, respectively:

wherein R₁ and R₂ are as described above. The synthesis of structure IVc may be accomplished by reacting structure III with phosphoryl chloride. Similarly, structure IVd may be synthesized by reacting thiosulfate with the reaction product of structure III or its sulfenyl chloride.

In yet a further embodiment of the present invention, the hydrolysis of the pantetheine ketal thioesters (i.e., structure IV above) to the corresponding pantetheine thioesters is disclosed. In this method, hydrolysis of the ketals under aqueous acid conditions yields the corresponding pantetheine thioesters . The hydrolysis of the ketals is facilitated under reaction conditions identical to the ketal hydrolysis described above in the sy.itheses of pantethine and pantetheine . The pantetheine thioesters produced by this method are represented by structure V :

wherein R3 is as described above. The synthesis of a representative pantetheine thioester, S-trimethylacetyl-D-pantetheine (i.e., structure V where R₃ = C (=O) C (CH₃)₃), by hydrolysis of the corresponding ketal under aqueous acidic conditions is described in detail in Example 7.

In addition to the ketals produced by the methods of the present invention, other 1,3-diol derivatives of pantethine and pantetheine may also serve as useful intermediates in the synthesis of highly pure pantethine, pantetheine, and pantetheine derivatives. As mentioned above, condensation with the 1,3-diol functional group present in pantetheine and its derivatives with ketones results in ketal formation. Condensation of the same 1,3-diols with other compounds may similarly afford crystalline, purifiable intermediates. In addition to ketones, 1,3-diols may- be condensed with aldehydes (R-CHO) to provide acetals (i.e, compounds of structure I' wherein either R₁ or R₂ is hydrogen and the other an alkyl, cycloalkyl, or aryl moiety as described above in the ketal discussion).

In addition to the condensation of the 1,3-diol functional group of pantetheine and its derivatives with ketones and aldehydes, these compounds may be treated with orthoester reagents. Orthoester reagents may be thought of as being derived from the addition of two equivalents of an alcohol (R_a-OH) to an ester (R_b-C (=O)-OR_a). Orthoester reagents are classified according to the ester and alcohols from which they are derived. Orthoester reagents derived from formate esters (R_b is hydrogen) are referred to as orthoformates, and orthoester reagents derived from all other esters (R_b not hydrogen) are referred to as the originating ester. For example, orthoesters derived from acetates (R_b is methyl) and benzoates (R_b is phenyl) are referred to as orthoacetates and orthobenzoates, respectively. Suitable orthoester reagents of the method of the present invention include orthoesters derived from esters and alcohols wherein R_b and R_a are as described for R₁ (and R₂) in the ketal discussion above. Preferred orthoesters include trimethyl orthoformate, trimethyl orthoacetate, and trimethyl orthobenzoate. For example, in the method of the present invention, treatment of pantothenic acid or its salts trimethyl orthoformate yields a cyclic orthoester according to structure I' wherein either R₁ or R₂ is hydrogen and the other is methoxy (i.e., R₁ = H and R₂ = OCH₃ or R₁ = OCH3 and R₂ = H)). Similar treatment with trimethyl orthoacetate or trimethyl orthobenzoate provide cyclic orthoesters where either R₁ or R₂ is methyl or phenyl, respectively, and the other is methoxy. Orthoesters derived from alcohols other than methanol may also be used in the practice of the present invention. Suitable alcohols include C₁ to C₁₀ alcohols, and provide orthoesters of formula I' where either R₁ or R₂ is a C₁ to C₁₀ alkoxy moiety.

Similarly, treatment of 1,3-diols such as pantothenic acid with orthocarbonate reagents (C(OR_a)₄) provide cyclic orthocarbonate derivatives of general formula I' wherein R₁ and R₂ are OR_a. For example, treatment of pantothenic acid with tetramethyl orthocarbonate (C(OCH₃)₄) provides an orthocarbonate derivative of formula I' wherein R₁ and R₂ are methoxy. Suitable orthocarbonate reagents are derived from alcohols (R_a-OH) wherein R_a is as described above for the orthoesters. Accordingly, the orthocarbonates of the present invention may be represented by formula I' where both R₁ and R₂ are C₁ to C₁₀ alkoxy moieties.

The formation of pantothenic acid derivatives described above, including acetals, orthoesters, and orthocarbonates, provide synthetic intermediates in the synthesis of pantethine, pantetheine, and pantetheine derivatives which are crystalline, readily purifiable by recrystallization, and, accordingly, may be utilized in the method of the present invention for the synthesis of highly pure pantethine, pantetheine, and pantetheine derivatives. The above-mentioned pantothenic acid derivatives are comparable to their ketal counterparts with respect to their ease of formation from pantothenic acid, purification by recrystallization, and hydrolysis to yield pantethine, pantetheine, and pantetheine derivatives in highly pure form (e.g., 99% or greater).

Certain physical data (i.e., proton NMR) of certain representative compounds of this invention are presented in Table 1.

The following examples are provided for purposes of illustration, not by way of limitation.

EXAMPLES

Example 1

Synthesis of 1,3-Isopropylidene-D-Pantothenic Acid

(Pantothenic Acid Acetone Ketal)

To a solution of 24.1 g (0.10 mole) sodium D-pantothenic acid in 250 mL methanol was added 9.1 g (0.10 mole) concentrated sulfuric acid by dropwise addition followed by the addition of 50 mL acetone. The mixture was evaporated to dryness at 45°C under reduced pressure.

To the resulting syrup was added 150 mL dimethoxypropane and 50 mL acetone. After heating the solution for 10 hours at 65°C, the solution was concentrated under reduced pressure to yield the crude product as a thick slurry.

The slurry was partitioned in 250 mL methylene chloride and 250 mL saturated aqueous sodium chloride. The methylene chloride layer was separated and washed with 100 mL saturated aqueous sodium chloride and dried over anhydrous sodium sulfate. Filtration of the drying agent and concentration to dryness produced a white powder (85% yield) . Recrystallization from acetone-hexane (1:1 v/v) gave 1,3-isopropylidene-D-pantothenic acid as a white crystalline solid , melting point 90 - 91 ° C (HPLC purity

> 99%) .

The recrystallized product was characterized by:

1H NMR: (see Table 1 above, compound D)

Elemental Analysis:

Calculated for C₁₂H₂₁NO₅:

%C=55.58, %H=8.16, %N=5.40

Found:

%C=55.34, %H=8.14, %N=5.37 Example 2

Synthesis of 1 , 3 -Isopropylidine-D-Pantethine

(Pantethine Acetone Ketal)

To a solution of 14.0 g (0.050 mole) 1,3-isopropylidene-D-pantothenic acid (prepared as described above in Example 1) in 140 mL tetrahydrofuran (dried over

4A molecular sieves) was added 0.10 g (0.050 mole) carbonyl diimidazole. The resulting solution was stirred at room temperature until the evolution of carbon dioxide gas had ceased (approximately 3 hours). To the solution was added 11.25 g (0.050 mole) cystamine dihydrochloride and the resulting solution heated at reflux for 6 hours.

The solution was concentrated under reduced pressure and the resulting white solid was dissolved in 150 mL methylene chloride. The methylene chloride solution was washed sequentially with solutions of saturated aqueous sodium chloride, dilute hydrochloric acid, saturated sodium bicarbonate, again with saturated aqueous sodium chloride, and dried over anhydrous sodium sulfate. The solution was filtered, diluted with 150 mL hexanes, and allowed to stand overnight at room temperature. The crystallized product was collected by filtration and recrystallized from ether-hexane (1:1 v/v) to yield 11.81 g (0.020 mole, 80% yield) 1,3-isopropylidene-D-panthethine as a white crystalline solid (melting point 117-118°C,

HPLC purity > 99%).

The recrystallized product was characterized by:

1H NMR: (see Table 1 above, compound B)

Elemental Analysis:

Calculated for C₂₈H₅₂N₄O₈S₂:

%C=52.81, %H=8.23, %N=8.69

Found:

%C=53.11, %H=8.02, %N=8.69 Example 3

Synthesis of D-Pantethine

A solution of 5.9 g (0.010 mole) 1,3-isopropylidene-D-pantethine (prepared as described above in Example 2) in 100 mL 80% aqueous acetic acid was heated for 6 hours at 65°C. The solution was concentrated to dryness under reduced pressure to provide a glassy solid. The solid was dissolved in 100 mL distilled water and washed with two 100 mL portions of methylene chloride. The aqueous layer was collected and freeze-dried to yield 4.75 g (0.0085 mole, 85% yield) D-pantethine as a white powder (hygroscopic, HPLC purity > 99%).

Example 4

Synthesis of 1,3-Isopropylidene-D-Pantetheine

(Pantetheine Acetone Ketal)

The synthesis of 1,3-isopropylidene-D-pantetheine from D-pantothenic acid was as described above in Example 2 for the synthesis of 1,3-isopropylidene-D-pantethine, except that cysteamine hydrochloride was used instead of cystamine dihydrochloride (white powder, 87% yield, HPLC purity > 99%). The recrystallized product was further characterized by ¹H NMR (see Table 1 above, compound A). Example 5

Synthesis of D-Pantetheine

The synthesis of D-pantetheine by hydrolysis of its acetone ketal (prepared as described above in Example 4) was as described above in Example 3 for the synthesis of D-pantethine (91% yield, white powder, hygroscopic, HPLC purity > 99%). Example 6

Synthesis of S-Trimethylacetyl- 1,3-Isopropylidene-D-Pantetheine

To a solution of 2.76 g (0.0010 mole) 1,3-isopropylidene-D-pantetheine (prepared as described above in Example 5) in 20 mL methanol was added a solution of sodium methoxide (freshly prepared from 0.23 g sodium in 20 mL methanol). The solution was concentrated to dryness under vacuum. The resulting powder was dissolved in 20 mL tetrahydrofuran (dried over 4A molecular sieves) and treated with 1.38 g (0.0110 mole) trimethylacetyl chloride (pivaloyl chloride). The solution was stirred for 1 hour at 25°C and evaporated to dryness. The residue was dissolved in 100 mL methylene chloride and washed sequentially with solutions of saturated aqueous sodium chloride, dilute hydrochloric acid, saturated sodium bicarbonate, again with saturated aqueous sodium chloride, and dried over anhydrous magnesium sulfate. The solution was filtered and evaporated to dryness to yield S-trimethylacetyl-1,3-isopropylidene-D-pantetheine as a clear, colorless oil (89% yield, HPLC purity > 99%). The compound was characterized by ¹H NMR (see Table 1 above, compound C). Example 7

Synthesis of S-Trimethylacetyl-D-Pantetheine S-trimethylacetyl-D-pantetheine was prepared by hydrolysis of its corresponding acetone ketal. Specifically, a solution of (0.010 mole) S-trimethylacetyl-1,3-isopropylidene-D-pantetheine (prepared as described above in Example 6) in 100 mL 80% aqueous acetic acid was heated for 6 hours at 65°C. The solution was concentrated to dryness under reduced pressure to provide a glassy solid. The solid was dissolved in 100 mL distilled water and washed with two 100 mL portions of methylene chloride. The aqueous layer was collected and freeze-dried to yield S-trimethylacetyl-D-pantethine as a glassy material (93% yield, HPLC purity > 99%).

From the foregoing, it will be appreciated that, although specific embodiments of the invention have been described herein for purposes of illustration, various modifications may be made without departing from the spirit and scope of the invention. Accordingly, the invention is not limited except by the appended claims.

Claims

1. A method of synthesizing a compound having structure I:

comprising reacting pantothenic acid or a salt thereof with a ketone and an acid, and obtaining the compound by crystallization, wherein R₁ and R₂ are the same or different and selected from hydrogen and a saturated or unsaturated, branched or unbranched, substituted or unsubstituted C₁ to C₁₀ alkyl moiety, C₃ to C₁₀ cycloalkyl moiety, C₆ to C₁₀ aryl moiety, C₁ to C₁₀ alkoxy moiety, and combinations thereof, or wherein R₁ and R₂ taken together form a C₁ to C₇ carbocycle moiety.

2. The method of claim 1 wherein R₁ and R₂ are the same or different and selected from a C₁ to C₇ alkyl moiety, a C₃ to C₇ cycloalkyl moiety, a C₆ to C₁₀ aryl moiety, and combinations thereof.

3. The method of claim 1 wherein both R₁ and R₂ are methyl moieties.

4. The method of claim 1 wherein the acid is an organic acid or a mineral acid.

5. The method of claim 4 wherein the organic acid is selected from a carboxylic acid, an ammonium salt, a sulfonic acid, and a sulfinic acid.

6. The method of claim 4 wherein the mineral acid is selected from hydrochloric acid, sulfuric acid, phosphoric acid, and nitric acid.

7. The method of claim 1, further comprising synthesizing a compound having structure II:

by reacting a compound having structure I with cystamine or a salt thereof, and obtaining the compound by crystallization, wherein R₁ and R₂ are the same or different and selected from hydrogen and a saturated or unsaturated, branched or unbranched, substituted or unsubstituted C₁ to C₁₀ alkyl moiety, C₃ to C₁₀ cycloalkyl moiety, C₆ to C₁₀ aryl moiety, C₁ to C₁₀ alkoxy moiety, and combinations thereof, or wherein R₁ and R₂ taken together form a C₁ to C₇ carbocycle moiety.

8. The method of claim 7 wherein R₁ and R₂ are the same or different and selected from a C₁ to C₇ alkyl moiety, a C₃ to C₇ cycloalkyl moiety, a C₆ to C₁₀ aryl moiety, and combinations thereof.

9. The method of claim 7 wherein both R₁ and R₂ are methyl moieties.

10. The method of claim 1, further comprising synthesizing a compound having structure III:

by reacting a compound having structure I with cysteamine or a salt thereof, and obtaining the compound by crystallization, wherein R₁ and R₂ are the same or different and selected from hydrogen and a saturated or unsaturated, branched or unbranched, substituted or unsubstituted C₁ to C₁₀ alkyl moiety, C₃ to C₁₀ cycloalkyl moiety, C₆ to C₁₀ aryl moiety, C₁ to C₁₀ alkoxy moiety, and combinations thereof, or wherein R₁ and R₂ taken together form a C₁ to C₇ carbocycle moiety.

11. The method of claim 10 wherein R₁ and R₂ are the same or different and selected from a C₁ to C₇ alkyl moiety, a C₃ to C₇ cycloalkyl moiety, a C₆ to C₁₀ aryl moiety, and combinations thereof.

12. The method of claim 10 wherein both R₁ and R₂ are methyl moieties.

13. The method of claim 7, further comprising hydrolyzing the compound having structure II to yield pantethine.

14. The method of claim 10, further comprising hydrolyzing the compound having formula III to yield pantetheine.

15. The method of claim 10, further comprising synthesizing a compound having structure IV:

comprising reacting the compound having structure III with an esterifying agent, and obtaining the compound by crystallization, wherein R₁ and R₂ are the same or different and selected from hydrogen and a saturated or unsaturated, branched or unbranched, substituted or unsubstituted C₁ to C₁₀ alkyl moiety, C₃ to C₁₀ cycloalkyl moiety, C₆ to C₁₀ aryl moiety, C₁ to C₁₀ alkoxy moiety, and combinations thereof, or where R₁ and R₂ taken together form a C₁ to C₇ carbocycle moiety, and wherein R₃ is a residual portion of the esterifying agent.

16. The method of claim 15 wherein the esterifying agent is selected from the group consisting of a reactive derivative of a carboxylic acid, a carbamic acid, phosphoric acid, and sulfuric acid.

17. The method of claim 15 wherein R₁ and R₂ are the same or different and selected from a C₁ to C₇ alkyl moiety, a C₃ to C₇ cycloalkyl moiety, a C₆ to C₁₀ aryl moiety, and combinations thereof.

18. The method of claim 15 wherein both R₁ and R₂ are methyl moieties.

19. The method of claim 15 wherein the esterifying agent is trimethylacetyl chloride.

20. The method of claim 15, further comprising synthesizing a compound having structure V:

by hydrolyzing the compound having structure IV, wherein R₃ is a residual portion of the esterifying agent.

21. The method of claim 20 wherein R₃ is a trimethylacetyl moiety.

22. A compound having the following structure:

wherein R₁ and R₂ are the same or different and selected from hydrogen and a saturated or unsaturated, branched or unbranched, substituted or unsubstituted C₁ to C₁₀ alkyl moiety, C₃ to C₁₀ cycloalkyl moiety, C₆ to C₁₀ aryl moiety, C₁ to C₁₀ alkoxy moiety, and combinations thereof, or wherein R₁ and R₂ taken together form a C₁ to C₇ carbocycle moiety.

23. The compound of claim 22 wherein R₁ and R₂ are the same or different and selected from a C₁ to C₇ alkyl moiety, a C₃ to C₇ cycloalkyl moiety, a C₆ to C₁₀ aryl moiety, and combinations thereof.

24. The compound of claim 22 wherein both R₁ and R₂ are methyl moieties.

25. A compound having the following structure:

26. The compound of claim 25 wherein R₁ and R₂ are the same or different and selected from a C₁ to C₇ alkyl moiety, a C₃ to C₇ cycloalkyl moiety, a C₆ to C₁₀ aryl moiety, and combinations thereof.

27. The compound of claim 25 wherein both R₁ and R₂ are methyl moieties.

28. A compound having the following structure

29. The compound of claim 28 wherein R₁ and R₂ are the same or different and selected from a C₁ to C₇ alkyl moiety, a C₃ to C₇ cycloalkyl moiety, a C₆ to C₁₀ aryl moiety, and combinations thereof.

30. The compound of claim 28 wherein both R₁ and R₂ are methyl moieties.

31. A compound having the following structure:

wherein R₁ and R₂ are the same or different and selected from hydrogen and a saturated or unsaturated, branched or unbranched, substituted or unsubstituted C₁ to C₁₀ alkyl moiety, C₃ to C₁₀ cycloalkyl moiety, C₆ to C₁₀ aryl moiety, C₁ to C₁₀ alkoxy moiety, and combinations thereof, or where Ri and R₂ taken together form a C₁ to C₇ carbocycle moiety; and wherein R3 is a residual portion of an esterifying agent.

32. The compound of claim 31 wherein R₁ and R₂ are the same or different and selected from a C₁ to C₇ alkyl moiety, a C₃ to C₇ cycloalkyl moiety, a C₆ to C₁₀ aryl moiety, and combinations thereof.

33. The compound of claim 31 wherein both R₁ and R₂ are methyl moieties.

34. The compound of claim 31 wherein R₃ is a trimethylacetyl moiety.

35. A compound having the following structure:

wherein R₃ is wherein R₃ is a residual portion of an esterifying agent.

36. The compound of claim 35 wherein both R₁ and R₂ are methyl moieties.

37. The compound of claim 35 wherein R₃ is a trimethylacetyl moiety.