Synthetic Confirmation of the Structure of the Lichen Benzyl Esters Alectorialic and Barbatolic Acids

Abstract

The total synthesis of methyl alectorialate (3) and methyl barbatolate (4) has been achieved, and the synthetic esters have been compared with naturally derived material. In addition alectorialin (decarboxylalectorialic acid) (5) and barbatolin (6) have been synthesized. The lichen Alectoria nigricans was shown to contain alectorialic acid (1), barbatolic acid (2), alectorialin (5) and 5,7-dihydroxy-6-methylphthalide (8), while the lichen Bryoria nadvornikiana was found to contain (1), (2), (5), barbatolin (6) and 6-formyl-5,7-dihydroxyphthalide (27).