CHLOROPEROXIDASE-INDUCED ASYMMETRIC SULFOXIDATION OF SOME CONFORMATIONALLY RESTRICTED SULFIDES

Asymmetric sulfoxidation by means of a chloroperoxidase from Caldariom yces fumago and hydrogen peroxide as the oxygen source was studied for a series of sterically well-defined substrates. The stereochemistry o f the sulfoxidation was the same for all substrates studied. While 2,3 -dihydrobenzo [b]thiophene (1) is an excellent substrate (giving 99.5% yield and 99% e.e. of the (R)-sulfoxide), replacement of a methylene group by either a more sterically demanding group or a heteroatom caus ed a substantial decrease in reactivity or in reactivity as well as en antioselectivity. A further investigation of the lowered catalytic eff iciency of chloroperoxidase with these substrates has been carried out in a series of competitive reactions. Thus, benzo[1,3]oxathiole (5) a cted as a competitive inhibitor of the enzyme, whereas 1-thiochroman ( 2) and 1-thiochroman-4-one (3) were shown to be too sterically demandi ng to significantly compete for the active site. For the oxidation of 2, 3, and 5, it was found that in the low CPO concentration range the chemical yield after 60 min reaction time increased almost linearly wi th the amount of CPO used. The products from 2 and 3 could be obtained in over 80% yield with an e.e. exceeding 96%. Chloroperoxidase was al so found to be an effective catalyst in the oxidation of labile episul fides, yielding the corresponding anti-sulfoxides quantitatively and g iving 12% e.e, of (1R, 2R)-sulfoxide in the oxidation of propylene sul fide. (C) 1998 Wiley-Liss. Inc.