Enzymatic Resolution of R,S

Examination of the results in Tab. 1 indicates that several enzymes are effident and seledive in the hydrolysis of the (R,S)-4, however most lipases preferentially hydrolyzed the (S)-ester while several proteases exhibited the desired (R)-ester selectivity. Based on these results, we focused all further efforts on the screening and optimization of inexpensive alkaline proteases. The corresponding butyl ester was also screened as a substrate. While several selective hydrolases were identified, the rate of hydrolysis was about three-fold less than that of ethyl ester (see Experimental), presumably due to the decrease in water solubility of the butyl ester. 

---

Xin J-Y, Zhao Y-J, Zhao G-L et al (2005) Enzymatic resolution of (R, S)-naproxen in water-saturated ionic liquid. Biocatal Biotransform 23 353-361... 

The enzymatic resolution of (R,S)-2-ethoxycarbonyl-3,6-dihydropyran has been carried out repeatedly in a pilot plant on a 100-125 kg scale. The conditions of pH, agitation, concentration, and enzyme/substrate ratio have been further optimized, but for the most part conditions developed during the laboratory optimization studies have been found to work well. This technology is currently being used to produce ton quantities of (S)-4. It has to be pointed out that no major difficulties were encountered during the scale-up. The work-up of the product in this process, unlike in many other enzyme-catalyzed processes, is quite simple and volume efficiencies are better than some chemical reactions. The recovery and recycling of the enzyme is not needed since it is commercially available and relatively inexpensive. 

Goswami A, Howell JM, Hua EY, et al. Chemical and enzymatic resolution of (R,S)-N-(tert-butoxycarbonyl)-3-hydroxymethylpiperidine. Organic Process Research and Development 5 4), 415, 2001. 

R. Scale-up of enantioselective reaction for the enzymatic resolution of (R,S)-ibuprofen. Biotechnol. Lett., 1995,17, 1095-1098. 

Recent studies in the pharmaceutical field using MBR technology are related to optical resolution of racemic mixtures or esters synthesis. The kinetic resolution of (R,S)-naproxen methyl esters to produce (S)-naproxen in emulsion enzyme membrane reactors (E-EMRs) where emulsion is produced by crossflow membrane emulsification [38, 39], and of racemic ibuprofen ester [40] were developed. The esters synthesis, like for example butyl laurate, by a covalent attachment of Candida antarctica lipase B (CALB) onto a ceramic support previously coated by polymers was recently described [41]. An enzymatic membrane reactor based on the immobilization of lipase on a ceramic support was used to perform interesterification between castor oil triglycerides and methyl oleate, reducing the viscosity of the substrate by injecting supercritical CO2 [42],... 

Palomo, J., G. Munoz, G. Femandez-Lorente, C. Mateo, M. Fuentes, J. M. Guisan, and R. Fernandez-Lafuente. 2003. Modulation of Mucor Miehei Lipase Properties Via Directed Immobilization on Different Hetero-Functional Epoxy Resins Hydrolytic Resolution of (R,S)-2-Butyroyl-2-Phenylacetic Acid. Journal of Molecular Catalysis B Enzymatic 21 (4-6) 201-210. 

Mugford, P.F., Lait, S.M., Keay, B.A. and Kazlauskas, R.J., Enantiocomplementary enzymatic resolution of the chiral auxiliary c7j,c7j-6-(2,2-dimethylpropanamido)spiro-[4.4]nonan- l-ol and the moleuclar basis for the high enantioselectivity of subtilisin Carlsberg. ChemBioChem, 2004, 5, 980-987. 

The procedure shows that it is feasible to combine racemization with the kinetic resolution process (hence the DKR) of R,S)- ethoxyethyl ibuprofen ester. The chemical synthesis of the ester can be applied to any esters, as it is a common procedure. The immobilized lipase preparation procedure can also be used with any enzymes or support of choice. However, the enzyme loading will need to be optimized first. The procedures for the enzymatic kinetic resolution and DKR will need to be adjusted accordingly with different esters. Through this method, the enantiopurity of (5)-ibuprofen was found to be 99.4 % and the conversion was 85 %. It was demonstrated through our work that the synthesis of (5)-ibuprofen via DKR is highly dependent on the suitability of the reaction medium between enzymatic kinetic resolution and the racemization process. This is because the compatibility between both processes is crucial for the success of the DKR. The choice of base catalyst will vary from one reaction to another, but the basic procedures used in this work can be applied. DKRs of other profens have been reported by Lin and Tsai and Chen et al. ... 

Enzymatic Resolution of /V-Acetyl-3-(9-oxo-9H-fluoren-3-yl)alanine (82) To Give (2S)-3-(9-Oxo-9H-fluoren-3-yl)alanine [(S)-69] and (2/ )-A-Acetyl-3-(9-oxo-9H-fluoren-3-yl)alanine [(R)-82] [153l... 

Enantioselective enzymatic transesterifications have been used as a complementary method to enantioselective enzymatic ester hydrolyses. The first example of this particular type of biotransformation is the synthesis of the optically active 2-acetoxy-l-silacyclohexane (5 )-78 (Scheme 19). This compound was obtained by an enantioselective transesterification of the racemic l-silacyclohexan-2-ol rac-43 with triacetin (acetate source) in isooctane, catalyzed by a crude lipase preparation from Candida cylindracea (CCL, E.C. 3.1.1.3)62. After terminating the reaction at 52% conversion (relative to total amount of substrate rac-43), the product (S)-78 was separated from the nonreacted substrate by column chromatography on silica gel and isolated in 92% yield (relative to total amount of converted rac-43) with an enantiomeric purity of 95% ee. The remaining l-silacyclohexan-2-ol (/ )-43 was obtained in 76% yield (relative to total amount of nonconverted rac-43) with an enantiomeric purity of 96% ee. Repeated recrystallization of (R)-43 led to an improvement of enantiomeric purity by up to >98% ee. Compound (R)-43 has already earlier been prepared by an enantioselective microbial reduction of the l-silacyclohexan-2-one 42 (see Scheme 8)53. The l-silacyclohexan-2-ol (R)-43 is the antipode of compound (.S j-43 which was obtained by a kinetic enzymatic resolution of the racemic 2-acetoxy-l-silacyclohexane rac-78 (see Scheme 15)62. For further enantioselective enzymatic transesterifications of racemic organosilicon substrates, with a carbon atom as the center of chirality, see References 64 and 70-72. 

As an alternative to the chemical resolution methods described by Atwal et al. (Scheme 4.13), a biocatalytic strategy towards the preparation of enantiopure (R) and (S)-SQ 32,926 was developed (Scheme 4.15). The key step in the synthesis is the enzymatic resolution of an N3-acetoxymethyl-activated dihydropyrimidone precursor by Thermomyces lanuginosus lipase [189]. The readily available racemic DHPM 43 was hydroxymethylated at N3 with formaldehyde, followed by standard acetylation with acetyl chloride. The resulting N3-acetoxymethyl-activated DHPM... 

Cotterill, I. C. Sutherland, A. G. Robert, S. M. Grobbauer, R. Spreitz, J. Faber, K. Enzymatic resolution of sterically demanding bicyclo[3.2.0]heptanes evidence for a novel hydrolase in crude porcine pancreatic lipase and the advantages of using organic media for some of the biotransformations. J. Chem. Soc. Perkin Trans 1991, 1, 1365. 

Goto, M., Noda, S., Kamiya, N., and Nakashio, R, Enzymatic resolution of racemic ibuprofen by surfactant-coated lipases in organic media, Biotechnol. Lett., 18, 839-844, 1996. 

Two approaches were studied to obtain (R)-l,3-BDO. The first was based on an enzyme-catalyzed asymmetric reduction of 4-hydroxy-2-butanone, and the second was based on enantioselective oxidation of the undesirable (S)-l,3-BDO in the racemate. As a result of screening for yeasts, fungi, and bacteria, the enzymatic resolution of racemic 1,3-BDO by Candida parapsilosis IFO 1396, which showed differential rates of oxidation for two enantiomers, was found to be the most practical process to produce (R)-l,3-BDO with high enantiomeric excess and yield. 

Optically active amines are important intermediates and chiral auxiliaries in the technical synthesis of agrochemicals and pharmaceuticals. BASF, one of the world s leading producers of chiral amines, developed a process based on the enzymatic resolution of racemic amines 49 with Burkholderia plantarii lipase immobilized on polyacrylate (Scheme 16) [75,76]. Methoxyacetic acid estars are particularly well suited for the stereospecific enzymatic differentiation, giving both the free amine (S)-49 and the acylated product R)-50 in high ee. The reaction stops at 50% conversion and the selectivity factor was calculated to be as high as 500. A plug-flow or batch reactor can be used for the enzymatic reaction and the residence time is in the range of 5-7 h. The more important amine (R)-49 can be liberated with the aid of base and is subsequently purified by distil-... 

The approach to the synthesis of (—)-swainsonine (378) adopted by Carre-tero and coworkers exploited the enzymatic resolution of the racemic alcohol (ib)-386 by enantiospecific esterification with vinyl acetate and lipase PS (Scheme 53) This reaction, when stopped at 50% conversion, afforded the alcohol (S)-386 and the ester R)-387 in ee of greater than... 

Ono, M., Ogura, Y., Hatogai, K., and Akita, H. (1995) Total synthesis of (S)-(-l-)-curcudiol, (S)- and (R)-(—)-curcuphenol based on enzymatic resolution of a primary alcohol possessing one stereogenic centre. Tetrahedron Asymmetry, 6,1829-1832. 

Conduritols and inositols are cyclic polyalcohols with significant biological activity. The presence of four stereogenic centers in the stmcture of conduritols allows the existence of 10 stereoisomers. Enzymatic methods have been reported for the resolution of racemic mixtures or the desymmetrization of meso-conduritols. For example, Mucor miehei lipase (MML) showed enantiomeric discrimination between all-(R) and all-(S) stereoisomers ofconduritol E tetraacetate (Figure 6.52). Alcoholysis resulted in the removal of the four acetyl groups ofthe all-(R) enantiomer whereas the all-(S) enantiomer was recovered [141]. 

The S- form of o-carboranylalanine was first synthesized in 1979 by the reaction of an optically active ethynylalanine derivative, obtained by enzymatic resolution, with decaborane(14), followed by hydrolysis (see Scheme 2.2-3) [23], Since then, several asymmetric syntheses of S- and R-enantiomers of o-carboranylalanine have been reported, including the use of stereoselective propargylation [24] and stereoselective introduction of an amino group [25],... 

Taylor, S.J.C., Sutherland, A.G., Lee, C., Wisdom, R., Thomas, S., Roberts, S.M. and Evans, C., Chemoenzymatic synthesis of (—)-carhovir utilizing a whole cell catalysed resolution of 2-azabicyclo[2.2.1 ]hept-5-en-3-one. J. Chem. Soc. Chem. Commun., 1990, 1120-1121 Evans, C.T., Roberts, S.M., Shoheru, K.A. and Sutherland, A.G., Potential use of carbocyclic nucleosides for the treatment of AIDS chemo-enzymatic syntheses of the enantiomers of carbovir. J. Chem. Soc. Perkin Trans. 1,1992, 589-592. 

Scheme 1.1 (R)-Selective enzymatic resolution with recycling of unreacted (S)-substrate.

Zopiclone is a chiral cyclopyrrolone with hypnotic properties, possessing a pharmaceutical profile of high efficacy and low toxicity, similar to that of benzodiazepines. Zopiclone has been commercialized as a racemic mixture however, the (S)-enantiomer is more active and less toxic than the (R)-enantiomer [11]. Although enzymatic hydrolysis of esters or transesteriflcation processes of alcohols have been widely applied for enzymatic resolution or desymmetrization... 

---