Pseudomonas cepacia lipase racemic resolution

M.S. Rasalkar, M.K. Potdar, M.M. Salunkhe, Pseudomonas cepacia lipase-catalysed resolution of racemic alcohols in ionic liquid using succinic anhydride role of triethylamine in enhancement of catalytic activity, J. Mol. Gatal. B Enzym. 27 (2004) 267-270. 

The resolution of a racemic substrate can be achieved with a range of hydrolases including lipases and esterases. Among them, two commercially available Upases, Candida antarctica lipase B (CALB trade name, Novozym-435) and Pseudomonas cepacia lipase (PCL trade name. Lipase PS-C), are particularly useful because they have broad substrate specificity and high enantioselectivity. They display satisfactory activity and good stability in organic media. In particular, CALB is highly thermostable so that it can be used at elevated temperature up to 100 °C. 

An interesting case is the resolution of a heterohelicenediol. The very bulky racemic substrate roc-15 is resolved by lipase-catalyzed acylation with vinyl acetate in dichloromethane. Oddly enough, Candida antarctica lipase (CAL) and Pseudomonas cepacia lipase (PCL) display opposite enantiopreferences [54]. In Scheme 4.13, only the remaining substrates are shown and not the other products, the mono- and diacetates. 

Racemic resolution of a-hydroxy esters was achieved with Pseudomonas cepacia lipase (PCL) and a ruthenium catalyst (for a list, see Figure 18.13) as well as 4-chlorophenyl acetate as an acyl donor in cyclohexane, with high yields and excellent enantiomeric excesses (Huerta, 2000) (Figure 18.14). Combining dynamic kinetic resolution with an aldol reaction yielded jS-hydroxy ester derivatives in very high enantiomeric excesses (< 99% e.e.) in a one-pot synthesis (Huerta, 2001). 

Drueckhammer and co-workers have published details of a successful strategy for dynamic resolution in the hydrolysis of suitable thioesters130, 321. Trioctylamine was employed as the racemizing agent, which was effective for the racemization of a series of a-substituted thiopropionates. Specific examples include the hydrolysis of an ethylthioester using Pseudomonas cepacia lipase, the transesterification of an a-aryloxy trifluoroethylthioester with butanol and PS-30, as well as hydrolysis of a trifluoroethylthioester using Subtilisin Carlsberg (Fig. 9-15). 

Table 11.1-20). A very good illustration for the potential of enantiomer-differentiating acylation catalyzed by lipases is provided by the high-yield synthesis of a series of aromatic cyanohydrin acetates (la-g) from aldehydes, acetone cyanohydrin and vinyl acetate in the presence of Pseudomonas cepacia lipase and a basic anion-exchange resin in diisopropyl ether which proceeds under kinetic resolution coupled with in situ formation and racemization of the cyanohydrin representing a dynamic kinetic resolution. For further examples see Table 11.1-24. 

Paclitaxel analogs bearing a side chain containing heterocyclic or cycloalkyl groups have also been shown to possess anticancer activity, and the enzymatic resolution of racemic mixtures of such intermediates has again been investigated at Bristol-Meyers Squibb [70]. Racemic ds-34 could be stereoselectively hydrolyzed by Pseudomonas cepacia lipase (Amano PS-30) immobilized on Ac-curel and led to high optical purities of the desired (3R,4R)-enantiomer 34 (Scheme 11). Contrary to the use of the free enzyme, the immobilization reduced the required amount of biocatalyst by a factor of 10. 

In 2000, an efficient DKR protocol for a-hydroxy esters was reported by Backvall et al. using Shvo s catalyst 1 for the racemization [73]. Pseudomonas cepacia lipase (PS-C) was used for the enzymatic resolution. The protocol was applicable to aromatic hydroxy acids with both electron-withdrawing and a-donating groups present on the aromatic ring. The corresponding acetates... 

An efficient DYKAT of a racemic cisitrans mixture of cyclohexane-1,3-diol using Shvo s complex 1 was reported in 2006 [85]. Pseudomonas cepacia lipase (PS-C) was used for the enzymatic resolution along with para-chlorophenyl acetate as the acyl donor. The cis-diacetate was obtained in 95% yield with high diaster-eoselectivity cisitrans = 97/3). 

Diols such as the optically active 1,1 -binaphthyl-2-2 -diol (BINOL) have been used as versatile templates and chiral auxiliaries in catalysts employed successfully in asymmetric synthesis. The application of enzymes in the enantioselective access to axially dissymmetric compounds was first reported by Fujimoto and coworkers.83 In aqueous media, the asymmetric hydrolysis of the racemic binaphthyl dibutyrate (the ester) using whole cells from bacteria species afforded the (A)-diol with 96%ee and the unreacted substrate (A)-ester with 94% ee at 50 % conversion. Recently, in non-aqueous media, lipases from Pseudomonas cepacia and Ps. fluorescens have been employed in the enantioselective resolution and desymmetrization of racemic 6,6 -disubstituted BINOL derivatives using vinyl acetate.84 The monoacetate (K)-73 (product) was obtained in 32-44 % chemical yields and 78-96% ee depending on the derivatives used. The unreacted BINOL (S)-72 was obtained in 30-52 % chemical yield and 55-80% ee. 

A one-pot synthesis of optically active cyanohydrin acetates from aldehydes has been accomplished by lipase-catalyzed kinetic resolution coupled with in situ formation and racemization of cyanohydrins in an organic solvent. Racemic cyanohydrins, generated from aldehydes and acetone cyanohydrin in diisopropyl ether under the catalysis of basic anion-exchange resin, were acetylated stereoselectively by a lipase from Pseudomonas cepacia (Amano) with isopropenyl acetate as an acylating... 

In an alternate process for the preparation of the C-13 paclitaxel side chain, the enantioselective enzymatic hydrolysis of racemic acetate ci5 -3-(acetyloxy)-4-phenyl-2-azetidinone 38 (Eignre 16.10B), to the corresponding (S)-alcohol 39 and the nnreacted desired (l )-acetate 38 was demonstrated [63] nsing lipase PS-30 from Pseudomonas cepacia (Amano International Enzyme Company) and BMS lipase (extracellnlar lipase derived from the fermentation of Pseudomonas sp. SC 13856). Reaction yields of more than 48% (theoretical maximnm yield 50%) with EEs greater than 99.5% were obtained for the (R)-38. BMS lipase and lipase PS-30 were immobilized on Accnrel polypropylene (PP), and the immobilized lipases were reused (10 cycles) without loss of enzyme activity, productivity, or the EE of the product (R)-38. The enzymatic process was scaled up to 250 L (2.5 kg substrate input) using immobilized BMS lipase and lipase PS-30. Prom each reaction batch, R-acetate 38 was isolated in 45 mol% yield (theoretical maximum yield 50%) and 99.5% EE. The (R)-acetate was chemically converted to (R)-alcohol 39. The C-13 paclitaxel side-chain synthon (2R,3S-37 or R-39) produced by either the reductive or resolution process could be coupled to bacattin III 34 after protection and deprotection to prepare paclitaxel by a semisynthetic process [64]. 

In an enzymatic resolution approach, chiral (+)-trans-diol 79 was prepared by the stereoselective acetylation of racemic diol with lipases from Candida cylindraceae and Pseudomonas cepacia. Both enzymes catalyzed the acetylation of the undesired enantiomer of racemic diol to yield monoacetylated product and unreacted desired (+)-tran5 -diol... 

Lipases from C. antarctica and P. cepacia showed higher enantioselectivity in the two ionic liquids l-ethyl-3-methylimidazolium tetrafluoroborate and l-butyl-3-methylimidazolium hexafluoroborate than in THE and toluene, in the kinetic resolution of several secondary alcohols [49]. Similarly, with lipases from Pseudomonas species and Alcaligenes species, increased enantioselectivity was observed in the resolution of 1 -phenylethanol in several ionic liquids as compared to methyl tert-butyl ether [50]. Another study has demonstrated that lipase from Candida rugosa is at least 100% more selective in l-butyl-3-methylimidazolium hexafluoroborate and l-octyl-3-nonylimidazolium hexafluorophosphate than in n-hexane, in the resolution of racemic 2-chloro-propanoic acid [51]. 

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