CAL-B-Catalyzed Alkoxycarbonylation of A-Ring Stereoisomeric Synthons of 1α,25-Dihydroxyvitamin D3and 1α,25-Dihydroxy-19-nor-previtamin D3: A Comparative Study. First Regioselective Chemoenzymatic Synthesis of 19-nor-A-Ring Carbonates | Publicación