Epimerization microbial

After recovery of L-lysine, the residual dl-(49) is epimerized to a mixture of the DL and meso isomers, and the latter is subjected to the same decarboxylation step. This reaction is a part of a microbial process in which glucose is fermented by a lysine auxotroph of E. coli to meso- which accumulates in the medium. Meso-(49) is quantitatively decarboxylated to L-lysine by cell suspensions oi erobacteraerogenes (93). However, L-lysine and some... 

A substantial number of PLP enzymes catalyze the racemization or epimerization of primary a-amino acids [54,55]. Of particular physiological importance are microbial alanine racemases because of their involvement in bacterial cell wall formation, which makes them a potential target for chemotherapy. An interesting substrate specificity is exhibited by diaminopimelate racemase [56] which acts only on meso-and LL-diaminopimelate, but not on the DD-isomer, i.e., the enzyme requires the L configuration at one end of the molecule in order to epimerize the chiral center at the other end. Racemization is also occasionally observed as an alternate catalytic... 

The intestinal microflora of man and animals can biotransform bile acids into a number of different metabolites. Normal human feces may contain more than 20 different bile acids which have been formed from the primary bile acids, cholic acid and chenodeoxycholic acid [1-5], Known microbial biotransformations of these bile acids include the hydrolysis of bile acid conjugates yielding free bile acids, oxidation of hydroxyl groups at C-3, C-6, C-7 and C-12 and reduction of oxo groups to give epimeric hydroxy bile acids. In addition, certain members of the intestinal microflora la- and 7j8-dehydroxylate primary bile acids yielding deoxycholic acid and lithocholic acid (Fig. 1). Moreover, 3-sulfated bile acids are converted into a variety of different metabolites by the intestinal microflora [6,7]. 

The biotransformations of 6)8-eudesmanolides functionalized at C(3), obtained from santonin, with Curvularia lunata and Rhizopus nigricans cultures have been also studied (Schemes 17 and 18) [27]. Rhizopus nigricans was more active in the biotransformation processes against these substrates. It is noteworthy that incubation of compound 109 with Rhizopus nigricans produced epimerization at C(4) and, in decreasing order, hydroxylation at C(8), C(l), or C(4). The authors attributed this epimerization to the participation of the hydroxyl group at C(3), and noticed that microbial functionalization at C(8) could provide access to the synthesis of 8,12-eudesmanolides. 

A combined enzymatic/chemical synthesis of imino-alditols used fructose 1,6-diphosphate aldolase to generate 6-azido-ketohexoses (as outlined in Scheme 4) which could be catalytically reduced to deoxynojirimycin and deoxymannojirimycin. By use of appropriate azido-aldehydes, fagomine(15) and 1,4-dideoxy-l,4-imino-D-arabinitol (16) were similarly prepared. Microbial epimerization of 1-deoxy-... 

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