Biocatalytic Racemization of α-Hydroxy Ketones (Acyloins) at Physiological Conditions usingLactobacillus paracasei DSM 20207

Naphthalenones and Naphthols Isolated from the Saussurea laniceps Endophytic Fungus Didymella glomerata X223

One new naphthalenone, didymelol A, and three new naphthols, didymelol B-D, together with three known naphthalenones, (3S,4R)-3,4,6-trihydroxy-3,4-dihydronaphthalen-1(2H)-one, (4S)-4,6-dihydroxy-3,4-dihydronaphthalen-1(2H)-one, (4S)-4-hydroxy-3,4-dihydronaphthalen-1(2H)-one, were isolated from the Saussurea laniceps endophytic fungus Didymella glomerata X223. The structures of the isolates were elucidated based on extensive spectroscopic data analysis. The absolute configuration of didymelol A was established through single-crystal X-ray diffraction data and didymelols B-D were identified through comparisons of experimental and calculated ECD spectra. All compounds were evaluated for cytotoxic activity against human non-small cell lung cancer A549 cells and human breast carcinoma MDA-MB-435 cells.

Emulation of Racemase Activity by Employing a Pair of Stereocomplementary Biocatalysts

Racemization is the key step to turn a kinetic resolution process into dynamic resolution. A general strategy for racemization under mild reaction conditions by employing stereoselective biocatalysts is presented, in which racemization is achieved by employing a pair of stereocomplementary biocatalysts that reversibly interconvert an sp3 to a sp2 center. The formal interconversion of the enantiomers proceeds via a prochiral sp2 intermediate the formation of which is catalyzed either by two stereocomplementary enzymes or by a single enzyme with low stereoselectivity. By choosing appropriate reaction conditions, the amount of the prochiral intermediate is kept to a minimum. This general strategy, which is applicable to redox enzymes (e.g., by acting on R2CHOH and R2CHNHR groups) and lyase-catalyzed addition-elimination reactions, was proven for the racemization of secondary alcohols by employing alcohol dehydrogenases. Thus, enantiopure chiral alcohols were used as model substrates and were racemized either with highly stereoselective biocatalysts or by using (rarely found) non-selective enzymes.

Biocatalytic racemization of sec-alcohols and α-hydroxyketones using lyophilized microbial cells

Biocatalytic racemization of aliphatic and aryl-aliphatic sec-alcohols and alpha-hydroxyketones (acyloins) was accomplished using whole resting cells of bacteria, fungi, and one yeast. The mild (physiological) reaction conditions ensured the suppression of undesired side reactions, such as elimination or condensation. Cofactor and inhibitor studies suggest that the racemization proceeds through an equilibrium-controlled enzymatic oxidation-reduction sequence via the corresponding ketones or alpha-diketones, respectively, which were detected in various amounts. Ketone formation could be completely suppressed by exclusion of molecular oxygen. Figure Biocatalytic racemization whole microbial cells.