Synthesis of Branched-Chain Sugars with a DHAP-Dependent Aldolase: Ketones are Electrophile Substrates of Rhamnulose-1- phosphate Aldolases

International audience; Dihydroxyacetone phosphate (DHAP)-dependent rhamnulose aldolases display an unprecedented versatility for ketones as electrophile substrates. We selected and characterized a rhamnulose aldolase from Bacteroides thetaiotaomicron (RhuABthet) to provide a proof of concept. DHAP was added as a nucleophile to several a-hydroxylated ketones used as electrophiles. This aldol addition was stereoselective and produced branched-chain monosaccharide adducts with a ter-tiary alcohol moiety. Several aldols were readily obtained in good to excellent yields (from 76 to 95 %). These results contradict the general view that aldehydes are the only electrophile substrates for DHAP-dependent aldolases and provide a new CÀC bond-forming enzyme for stereoselective synthesis of tertiary alcohols.