(−)-Daucic acid: Proof of d- lyxo configuration, synthesis of its d- ribo, d- xylo, l- arabino and l- lyxo analogs, and biosynthetic implications

Abstract

The dimethyl esters of the 2,6-anhydro-3-deoxy-hept-2-enaric acids with d- xylo, d- lyxo, l- arabino, l- lyxo- and d- ribo-configuration were synthesized from d-galactose and d-mannose, respectively, and further characterized by their di- O-acetyl and di- O-benzoyl derivatives. Comparison of their physical data with those of Daucus carota derived products revealed (−)-daucic acid to have d- lyxo-configuration 46 rather than the previously assigned d- xylo stereochemistry 1. Dimethyl daucate 43 could be converted by acid-induced ring contraction and dehydration into naturally occurring (+)-osbeckic acid 47, thereby proving its ( S)-configuration. Configurational identity in the pyranoid rings of (−)-daucic acid and KDO, together with available biosynthetic evidence on chelidonic acid 4, a leaf closing factor, suggests a joint, KDO 8-P-based pathway for their biosynthesis in plants.