A Biocatalytic Approach to the Enantioselective Synthesis of (R)- and (S)-Malic Acid
(S)-Diethyl malate 1a was prepared (70-80percent yield; >98percent optical purity) by an enantioselective reduction of sodium diethyl oxalacetate 2 by fermenting baker's yeast (Saccharomyces cerevisiae).Other microorganisms were tested for their capability of reducing 2.Most of them afforded (S)-1a with ee from 8 to 94percent and only Candida utilis, Aspergillus niger and Lactobacillus fermentum ILC G18D preferentially reduced compound 2 to (R)-1a. (R)-Dimethyl malate 1b was obtained from (R,S)-malate 1b by hydrolysis with pig liver esterase (PLE), the highest ee (93percent) being realized at 0 deg C in 20percent aqueous methanol.Enzymatic hydrolyses of protected malates 1d and 1e did not lead to improvement of the ee.
STEREOCHEMICAL STUDIES ON BORONOLIDE, AN α-PYRONE FROM TETRADENIA BARBERAE
Key Word Index-Tetradenia barberae; Lamiaceae; α-pyrone; boronolide. The structure of boronolide isolated from Tetradenia barberae has been confirmed as 6R--5,6-dihydro-2H-pyran-2-one by chemical degradation.
Davies-Coleman, Michael T.,Rivett, Douglas E. A.
p. 3047 - 3050
(2007/10/02)
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