STEREOSPECIFIC ELIMINATION OF HYDROGEN-ATOMS WITH OPPOSITE ABSOLUTE ORIENTATIONS DURING THE BIOSYNTHESIS OF ORSELLINIC ACID FROM CHIRAL MALONATES IN PENICILLIUM-CYCLOPIUM

(R)-[1-C-13; 2-H-2]Malonate and (S)-[1-C-13; 2-H-2]malonate are transformed, using succinyl-CoA transferase, into their paired chiral malonyl-CoA derivatives; incorporation of the malonyl-CoA derivatives into orsellinic acid is accomplished using homogeneous orsellinic acid synthase from Penicillium cyclopium; mass spectrometric analysis of the orsellinic acid reveals that the hydrogen atoms eliminated from the methylene groups at the 2- and 4-positions of the putative polyketide intermediate are from opposite absolute orientations in malonyl-CoA.