MXPA99011966A - Process for preparing enantiomerically enriched n-derivatised lactams - Google Patents

Abstract

The present invention relates to a process for the production of substantially enantiomerically pure intermediates of formula (IV), wherein P is an activating and protecting group, from their racemates by treating the mixture with an acylase enzyme derived from Bacillus sp..

Description

PROCESS FOR PREPARING LACTA AS N-DERIVATIVES ENRIQUECIDAS E-KAN IOM? RICAMENE The present invention relates to a process for the preparation of (IR, 4S) -2-azabicyclo [2.2. l] hept-5-en-3-ones N-derivatives, enantiomerically enriched. Abacavir, a nucleoside analog of 2-aminopurine with the following structure (I) known from EP 0434 450, it has potent activity against the human immunodeficiency virus (HIV) and the hepatitis B virus. There is a need to synthesize large amounts of abacavir for clinical trials. In the future, once the abacavir has been approved by the REF .: 32350 national agencies of regulation of medicines, will also be required large quantities for sale as a prescription medicine for the treatment of HIV infections. An important step in the manufacture of abacavir is the preparation of an enantiomerically pure, substituted cyclopentane ring. Existing methods are already known which start from a lactam of the formula (II) EP-A-0424064 describes a process in which the racemic lactam (II) prepared by the reaction of cyclopentadiene with tosyl cyanide, can be reacted with lactamases that will give a single cis enantiomer, or a mixture of cis enantiomers which is enriched with respect to one of the enantiomers, of the open compound of the ring (III) together with the unreacted lactam which is enantiomerically enriched with respect to one or the other enantiomer. A high-throughput and cost-effective process for the production of substantially pure enantiomerically intermediate compounds of the formula (IV) has now been developed. where P is a protection and activation group from their racemates.

It has been found that the derivatization of the nitrogen atom of the lactam in the compound of the formula (II) with a group P [as in the following formula (V)] activates the binding of the lactam for hydrolysis. It has surprisingly been found that the enzymes obtainable more easily than those described in EP-A-042064 and which appear, under normal conditions, to have no activity in relation to the lactam of the formula (II) described in the EP-A patent -0424064, can be used to produce the compounds of the formula (IV). According to one aspect of the present invention, therefore, a process is provided for the enantiomeric resolution of a racemic mixture of (±) 2-azabicyclo [2.2.1] hept-5-en-3-one N- protected (V) Where P is an activation and protection group, to give the (IR, 4S) -2-azabicyclo [2.2. l] hept-5-en-3-one N-protected substantially pure enantiomerically, treating the mixture with an acylase enzyme. According to a further aspect of the present invention, there is provided a process for the preparation of substantially enantiomerically pure (N, protected) N-protected (IR, 4S) -2-azabicislo [2.2.1] hept-5-en-3-one from formula (IV), above, wherein P is an activation and protection group, wherein a racemic mixture of (±) 2-azabicyclo [2.2.1] hept-5-en-3-one N-protected from the formula (V), above, wherein P is an activation or protection group, is treated with an acylase enzyme and the unreacted enantiomer of formula (IV) is isolated from the reaction mixture by conventional techniques. It is preferred that the activation / protection group is a substituted oxycarbonyl or acyl group. Preferred acyl groups include formyl or lower alkanoyl (having for example 1 to 4 carbon atoms in the alkyl portion), especially an acetyl group. Preferred substituted oxycarbonyl groups will be of the formula ROC (O) -, where R can be an alkyl or aralkyl group. A preferred alkyl group is tert-butyl. A possible aralkyl group is "benzyl," since it has also been found that substantial deprotection of these protected compounds can occur under aqueous conditions., it is preferred that the reaction be carried out in a mixture of organic solvent and water. It is preferred to use organic solvents miscible in water, such as cyclic ethers, for example tetrahydrofuran or 1,4-dioxane. To minimize deprotection it is preferred to use less than 70% water, more preferably about 50% or less (by volume). A mixture of tetrahydrofuran and water of approximately 50:50 (v / v) has been found more suitable. When used as above, the reaction in general can be carried out in a single phase. However, there is no reason why the use of an organic solvent to create a two-phase system could not be successful, such as with aromatic hydrocarbons. While the reaction is complete, the (IR, 4S) -2-azabicyclo [2.2. l] hept-5-en-3-one of the formula (IV) N-protected essentially pure enantiomerically, and the one that did not react, can be isolated from the reaction mixture by conventional techniques, such as solvent extraction. Several acylase enzymes have been found which enantioselectively hydrolyse the lactam binding to leave the desired isomer underneath. Enzymes derived from Bacillus sp. Which show in particular the right profile of activity. For example, S? Btillsin carlsberg (ALTUS) provides the "(IR, 4S) -2-azabicyclo [2.2.1] hept-5-en-3-one N-protected, (IV) P = tert-butyl oxycarbonyl] of the racemic mixture (V) in an enantiomeric excess of 73%. Other enzymes include Bacillus sp. protease, Neutrase, Novoenzyme 243, Alcalase and Savinasa and are commercially available from ALTUS and NOVO. Enzymes from other sources that show enantioselective hydrolysis can also be used, such as pig liver esterase (ALTUS), porcine pancreatic lipase (Biocatalysts), Flavorpro-192 (peptidase, Biocatalysts), Flavorpro-373 (glutaminase, Biocatalysts), Promod-TP (endopeptidase, Biocatalysts), lipase-CE (Humicola lan? Ginosa, Amano), protease-M . { Aspergillus sp. , Amano), prozima-ß (Aspergillus sp., Amano), lipase PGE (salivary gland and calf root, Amano) and Aspergillus sp. acylase (Sigma). Preferably, the commercially available acylase enzyme Savinasa (NOVO) will be used because it has been found to show bioconversion rates of (1S, 4R) -2-azabicyclo [2.2.1] hept-5-en-3-one N-protected suitable for industrial scale applications. Savinasa is a proteolytic enzyme prepared by the submerged fermentation of a Bacillus alkalophilic species. It is a serine endoprotease of the serine. In tests that have been carried out, this enzyme has not shown any ability to hydrolyze a racemic mixture of the non-acylated lactam of formula (II), under conditions of normal use. The bioconversion of N-protected (lS, 4R) -2-azabicyclo [2.2.1) hept-5-en-3-one will desirably be carried out within a pH range of 6 to 11, preferably 7 to 9. A temperature within the range of 20 to 50 ° C will be preferably used. It is even more preferred to carry out the process at a pH of about 8 and at a temperature of about 30 ° C. A ratio of Savinasa: substrate in the range from 1: 1 to 10: 1 for example from 2: 1 to 5: 1 (w / w) produces a fast, clean reaction. The optimal ratio for a given enzyme can be easily determined by simple experimentation. The starting compounds of the formula (V) in which P is tert butyloxycarbonyl can be prepared from the corresponding non-protected racemic lactam of the formula (II) by methods analogous to those described in Taylor et al., Tet. Asym etry, 4, p. 1117 (1993). The compounds of the formula (V) in which P is formyl or lower alkanoyl can be prepared from the corresponding non-protected racemic lactam of the formula (II) by the methods described in TW Greene, "Protective Groups in Organic Synthesis ", Wiley, New York, pp. 218-287 and J.F.W. McOmie, "Protective Groups in Organic Chemistry," Plenum Press, New York, 1973, p. 43-93, or by analogous methods. The compound of the formula (IV) can be easily converted to the corresponding N-protected amino acid by hydrolysis. The N-protected amino acid can be easily converted to the corresponding amino alcohol of the formula (VI) by reagents capable of converting carboxylic acids to alcohols, for example lithium aluminum hydride or borane. Alternatively, the compound of formula (IV) can be converted directly to the corresponding open ring amino alcohol of formula (VI) using sodium borohydride by methods such as those described in Tet. Asymm, 4, p 1117 (1993). The following examples are proposed for illustration only and are not intended to limit the scope of the invention in any way.

Example 1 Several hydrolytic enzymes were selected to verify the ability to hydrolyze the lactam binding of (+) 3-oxo-2-azabicyclo [2.2. l] butyl tert-5-en-2-carboxylate [(V), P = tert butyl oxycarbonyl] enantioselectively. The reactions were carried out at room temperature in magnetically stirred glass ampoules (working volume of 4 ml) containing 1 mg / ml of the racemic compound in 50% tetrahydrofuran buffer solution: 50% phosphate (v / v) (50 mM, pH 7) at room temperature. Each enzyme was added to give a final concentration of 25 mg / ml. This represents a ratio of 25: 1 (p: p) of the enzyme to the substrate, which for screening purposes should detect any possible hydrolytic activity. Containers without enzymes served as controls. Periodically, the samples were removed and diluted 1: 2 with water prior to the analysis by cyan.

Ciar condition: Column: Spherisorb C6 (15 x 0.46 cm). Isocratic at room temperature at 1 ml / min. Mobile phase: 30% (v / v) acetonitrile containing 0.1% v / v of formic acid. Detection of the wavelength at 200 nm.

It has been shown that the chemical hydrolysis of (±) 3-Oxo-2-azabicyclo [2.2.1] hept-5-en-2-carboxylate of tert-butyl was negligible under the conditions of the reaction. Several enzymes appear to hydrolyze the racemic compound enantioselectively to give the (-) (IR, 4S) 3-oxo-2-azabicyclo [2.2.1] hept-5-en-2-carboxylate of tert-butyl as evidenced by a sign negative rotation by the chiralizer (detector of optical rotation by CLAR). The savinase was chosen for further investigation. The reaction mixture, containing about 50% of the starting material, was analyzed by chiral and residual lactam was shown to have an enantiomeric excess of 96.3%. In addition, the residual substrate was of the correct absolute configuration for the synthesis of abacavir.

Ciar güira]: Column: Chiralcel OD-H (25 x 0.46 cm). Isocratic at 5 ° C at 0.5 ml / min. Mobile phase: 2% (v / v) isopropyl alcohol / heptane. Detection of the wavelength at 205 nm.

Comparative Example 1 A solution containing the lactam (±) 2-azabicyclo [2.2. 1] hept-5-en-3-one racemic (II) at 1 mg / ml (working volume of 4 ml) was treated with Savinase (obtainable from NOVO) (25 mg / ml) in a buffer solution, 50% tetrahydrofuran: 50% phosphate (50 inM, pH 7). A container without enzyme served as control. Periodically, the samples were removed and diluted 1: 2 with water prior to the analysis by cyan.

Ciar: Column: Spherisorb C6 (15 x 0.46 cm). Isocratic at room temperature at 1 ml / min. Mobile phase: 4% (v / v) acetonitrile containing 0.1% (v / v) formic acid. Detection of the wavelength at 200 nm.

There is no reaction after 4 days of incubation at room temperature.

Example 2 Savinase (30 g, NOVO) was added to a solution (500 ml) containing 10 g of (+) 3-oxo-2-azabicyclo [2.2.1] hept-5-en-2-carboxylic acid tert-butyl ester [ (V), P = tert butyl oxycarbonyl] in 50.50 (v / v) tetrahydrofuran / 50 mM phosphate pH '8.0 at 30 ° C. The reaction was verified by CLAR for up to 2 days. While the reaction is complete (ca. 51% conversion, enantiomeric excess of (-) (IR, 4S) 3-oxo-2-azabicyclo [2.2.1] hept-5-en-2-carboxylate of tert butyl >99.8%), the enzyme was filtered and the pH of the rinsed solution was raised to 9 with a solution of sodium bicarbonate. This is then extracted with 3 x 200 ml of cyclohexane. The combined organic phase is extracted again with 100 ml of sodium bicarbonate solution and subsequently washed with 100 ml of brine. Evaporation and drying afforded a free flowing white solid (4.2 g, 84% theoretical theoretical yield). This was identified as (-) (IR, 4S) 3-oxo-2-azabicyclo [2.2.1] hept-5-en-2-carboxylic acid tert-butyl ester by NMR; enantiomeric excess > 99.8% by chiral HPLC.

Ciar chiral: Column: Chiralcel OD-H (25 x 0.46 cm). Isocratic, 0.5 ml / minute. Mobile phase: 2% (v / v) isopropyl alcohol / heptane. Detection of the wavelength at 205 nm. Temperature at 5 ° C.

Example 3 A solution of (-) (1R, 4S) 3-OXO-2-azabicyclo [2.2. l] Hert-5-en-2-carboxylic acid ester from above (3.5 g) in tetrahydrofuran (10 mL) was added to a suspension of sodium borohydride (1.27 g) in methanol (10 mL) and the mixture was stirred at about 20 ° C for about 18 hours. Additional amounts of tetrahydrofuran (10 ml) and sodium borohydride (1.27 g) are added and stirring is continued for about an additional 2 hours. 2 molar hydrochloric acid (30 ml) is added with caution, followed by toluene (20 ml). The two layers were separated, and the aqueous layer was further extracted with (2 x 25 ml). The combined organic extracts were washed with brine (20 ml), dried over sodium sulfate and evaporated to give the acid butyl ester (IR, 4S) (4-hydroxymethyl) -cyclopent-2-en-1-yl. carbamic (3.23 g) with an enantiomeric excess of 99.2% by chiral as a thin yellow gum, which was identical spectroscopically and chromatographically to an authentic sample.

Ciar chiral: Column: Chiralcel OD (25 X 0.46 cm). Flow: 1.0 mi / min. Mobile phase: 3% (v / v) isopropyl alcohol / heptane. Detection of the wavelength at 205 n.

Temperature at 35 C Example 4 Savinase was tested to verify the ability to hydrolyze the lactam binding of cis-2-acetyl-2-aza-bicyclo [2.2. l] hept-5-en-3-one racemic enantioselectively. The reaction was carried out in a magnetically stirred glass vial (working volume of 4 ml) containing 1 mg / ml of the substrate in a 50% buffer solution of tetrahydrofuran: 50% phosphate (v / v) (50 mg / ml). mM, pH 7) at room temperature. The reaction was started by adding Savinasa to a final concentration of 25 mg / ml. A container without enzyme served as control. Periodically, the samples were removed and diluted 1: 2 with water prior to the cyan analyzes.

Ciar: Column: Spherisorb C6 (15 x 0.46 cm). Isocratic at 20 ° C at 1 ml / min. Mobile phase: 5% (v / v) acetonitrile containing 0.1% formic acid (v / v). Detection of the wavelength at 210 nm.

Ciar chiral: Column: Chiralpak AD (25 x 0.46 cm). Isocratic at 20 ° C at 1 ml / min. Mobile phase: 2% (v / v) ethanol / heptane Detection of the wavelength at 215 nm.

It has been shown that, in the absence of the enzyme, the chemical hydrolysis of the substrate was negligible under the conditions of the reaction. However, there is a significant non-enzymatic hydrolysis of the substrate if the tetrahydrofuran was omitted from the reaction mixtures. Savinase hydrolysed racemic cis-2-acetyl-2-azabicyclo [2.2.1] hept-5-en-3-one enantioselectively to give (-) (IR, 4S) 2-acetyl-2-aza-bicyclo [ 2.2.1] hept-5-en-2-one as evidenced by a negative rotation sign by the chiralizer and by chiral cyan analysis. The reaction mixture, containing about 50% of the starting material was analyzed by chiral a two days and the residual lactam was demonstrated, by comparison with an authentic sample, having an enantiomeric excess of > 99.8% with the absolute configuration corrected for the synthesis of abacavir.

It is noted that in relation to this date, the best method known to the applicant, to implement said invention is that which is clear from the manufacture of the objects to which it refers. Having described the invention as above, the content of the following is claimed as property.

Claims (14)

1. A process for the preparation of the (IR, 4S) -2-azabicyclo [2.2.1] hept-5-en-3-one N-protected substantially pure enantiomerically, of the formula (IV) where P is a protective and activation group, characterized in that a racemic mixture of the (±) -2-azabicyclo [2.2.1) hept-5-en-3-one N-protected (V) where P is a protective and activation group is treated with an acylase enzyme and the unreacted enantiomer of the formula (IV) is isolated from the reaction mixture by conventional techniques.
2. 2. OR? process for the enantiomeric resolution of a racemic mixture of (±) 2-azabicyclo [2.2.1] hept-5-en-3-one (V) wherein P is a protecting and activating group, to give the (N, 4S) -2-azabicyclo [2.2.1] hept-5-en-3-one (IV) N-protected substantially enantiomerically pure, treating the mixture with an acylase enzyme.
3. 3. A process according to claim 1 or claim 2, characterized in that P is an acyl or oxycarbonyl group.
4. 4. A process according to any of claims 1 to 3, characterized in that P is a formyl or alkanoyl group having 1 to 4 carbon atoms.
5. 5. A process according to any of claims 1 to 3, characterized in that P is an alkoxycarbonyl or aralkyloxycarbonyl group.
6. 6. A process according to claim 5, characterized in that P is a tert-butyloxycarbonyl or benzyloxycarbonyl group.
7. 7. A process according to any of the preceding claims, characterized in that the acylase enzyme is derived from Bacillus sp.
8. 8. A process according to claim 7, characterized in that the acylase enzyme is Savinase.
9. 9. A process according to any of the preceding claims, characterized in that the reaction is carried out in a mixture of organic solvent and water.
10. 10. A process according to claim 9, characterized in that the organic solvent is an organic solvent miscible in water and less than 70% water by volume is used.
11. 11. A process according to claim 10, characterized in that the organic solvent miscible in water is tetrahydrofuran or 1,4-dioxane.
12. 12. A process according to any one of the preceding claims, characterized in that the reaction is carried out within a pH range of 6 to 11 and at a temperature of 20 to 50 ° C.
13. 13. A process according to claim 12, characterized in that the reaction is carried out at a pH of about 8 and at a temperature of about 30 ° C.
14. 14. A process according to any of the preceding claims, characterized in that the (IR, 4S) -2-aza-bicyclo [2.2.1] hept-5-en-3-one N-protected of the formula (IV) is isolated by solvent extraction.