Extractives from Guttiferae. Part XXI. The isolation and structure of nine coumarins from the bark of Mammea africana G. Don

Abstract

Four 4-n-propyl-, one 4-n-pentyl-, and four 4-phenyl-coumarins have been isolated from the bark of Mammea africana G. Don and identified. All are derived from 5,7-dioxygenated coumarins, and eight of the structures contain an isoprene unit and an acyl side chain at either C-6 or C-8. In four cases the isoprene unit exists as a 3-methylbut-2-enyl side chain but otherwise it forms part of a chromen or benzofuran system. The metabolites are 5,7-dihydroxy-6-(3-methylbut-2-enyl)-8-(2-methylbutyryl)-4-n-propylcoumarin (1)(mammea B/BB) 5,7-dihydroxy-8-(3-methylbut-2-enyl)-6-(3-methylbutyryl)-4-phenylcoumarin (5)(mammeisin, mammea A/AA) 5,7-dihydroxy-8-(3-methylbut-2-enyl)-6-(2-methylbutyryl)-4-phenylcoumarin (7)(mammea A/AB, MAB 1), 5,7-dihydroxy-8-(3-methylbut-2-enyl)-6-(2-methylbutyryl)-4-n-propylcoumarin (8)(MAB 2), 4′,5′-dihydro-5-hydroxy-5′-(1-hydroxy-1-methylethyl)-6-(2-methylbutyryl)-4-phenylfuro[2′,3′ : 7,8]coumarin (9)(MAB 3), 4′,5′-dihydro-5-hydroxy-5′-(1-hydroxy-1-methylethyl)-6-(2-methylbutyryl)-4-n-propylfuro[2′,3′ : 7,8]coumarin (10)(MAB 4), 5-hydroxy-6′,6′-dimethyl-6-(2-methylbutyryl)-4-phenylpyrano[2′,3′ : 7,8]coumarin (11)(MAB 5), 5-hydroxy-6′,6′-dimethyl-6-(2-methylbutyryl)-4-n-propylpyrano[2′,3′ : 7,8]coumarin (12)(MAB 6) and 5,7-dihydroxy-8-(2-methylbutyryl)-4-n-pentylcoumarin (13). The structures of the pyranocoumarins have been confirmed by partial synthesis. The possible biogenetic relationship between the coumarins and xanthones in Guttiferae is discussed.