Chiral carboxylic acids, enzymatic synthesis

The synthesis of chiral carboxylic acids by enzymatic resolution of the corresponding racemate is a widely established method, and for this purpose a broad variety of esterases are commercially available. Consequently, this... 

The second chirality source used in the synthesis of aminocyclopropane carboxylic acids was D-glyceraldehyde acetonide, which after Wittig-Homer-Emmons reaction provided the alkenes 61. Treatment with diazomethane and subsequent irradiation at low temperatures alforded the cyclopropanes 62, which were converted into several other derivatives by modification of the side chain (Scheme 11). Notably, the best results were obtained by irradiating in the presence of benzophenone as triplet sensitizer [33, 34]. Following a similar synthetic procedure allocoronamic acid 65 was prepared, which is one of the amino acids that can be processed by plant tissues and promises the possibility to control the enzymatic processes underlying plant growth and fruit ripening [35]. 

Aziridine carboxylates are chiral intermediates for the synthesis of -lactams and amino acids [200]. The use of enantioselective ester hydrolysis in the synthesis of optically active A -unsubstituted and A-substituted aziridine carboxylate by Candida cylindraceae lipase has been demonstrated by Bucciareli et al. [199]. Racemic methyl aziridine-2-car-boxylate and 2,3-dicarboxylate 110 were used as substrates both for enzymatic hydrolysis and for the synthesis of AAchloro, iV-acyl and A-sulfonyl derivatives (Fig. 38). The reaction yield of 35-45% (theoretical maximum yield is 50%) and the e.e. s of 90-98% were obtained depending on substrate used in the reaction mixture. 

---