Stereochemical assignment of 2,3-epoxy-2-methylbutanoate esters in naturalproducts

Inspection of the 182 known natural products containing 2,3-epoxy-2-methylb utanoate ester residues revealed a very high tendency in nature for the pre ferential epoxidation of (Z)-2-methyl-2-butenoate esters (angelates) over ( E)-2-methyl-2-butenoate esters (tiglates), since 177 compounds contain epox yangelate and only five have epoxytiglate ester residues. The absolute conf iguration of the epoxde group has been determined for 22 compounds, again s howing a very high natural stereoselectivity, since 20 compounds have the ( 2R,3R) and only two the (2S,3S) absolute configuration. In contrast, unconf irmed stereochemical predictions for an additional 21 compounds suggest tha t 12 have the (2S,3S) and 9 the (2R,3R) configuration. Botanical sources, H -1-NMR data of the epoxide-containing ester residue and molecular structure s were compiled, and methodologies are presented to determine or to further support the absolute configuration of the 2,3-epoxy-2-methylbutanoate este r residues, based on a chemical correlation with (R)- or (S)3-methyl-1,2-bu tanediol or on partial synthesis. Copyright (C) 1999 John Wiley & Sons, Ltd .