BISVERTINOLS: A NEW GROUP OF DIMERIC VERTINOIDS FROM VERTICILLIUM INTERTEXTUM

Article abstract of DOI:10.1016/S0040-4020(01)87382-8

From the culture medium of Verticillium intertextum four new metabolites were isolated, namely bisvertinol (5), dihydrobisvertinol (6), isodihydrobisvertinol (7) and bisvertinolone (8), all derivatives of the ring system D, namely 1,4,4a,6,8-pentahydroxy-4,5a,7,9b-tetramethyl-3,4,4a,5a,9a,9b-hexahydrodibenzofuran.The differences between 5, 6 and 7 are solely due to the side chains: 5 bears two sorbyl groups (CO-A), one at C(9) and the other at C(2), 6 has a sorbyl group (CO-A) at C(9) and a 2,3-dihydrosorbyl group (CO-B) at C(2), while 7 carries CO-A at C(2) and CO-B at C(9).Hydrogenations of 5, 6 and 7 gave the same octahydrobisvertinol (9), which consists of the ring system D carrying two tetrahydrosorbyl groups (CO-C) at C(2) and C(9).Methylation of 5, 6 and 7 with diazomethane afforded the monomethyl ethers 10, 11 and 12, respectively.The ring system of 8 differs from that of 5-7 in that the C(3)-methylene group is replaced by a carbonyl group.Like 5, 8 bears two sorbyl groups at C(2) and C(9).Compounds of the type 5-8 are called bisvertinols.The constitutions of the bisvertinols 5-7 follow from their spectroscopic properties (1H, 13C NMR, UV, and mass spectra) and from the hydrogenation results.The spectral interpretation led to possible partial structures and their combination was assisted by the computer program CONGEN.The constitution of 8 was derived by comparison of its spectral properties with those of 5.As a model for a part of the structure of 8, 2-<(E,E)-hexadienoyl>-3-hydroxy-5,5-dimethyl-2-cyclohexen-1-one (17) was prepared.The bisvertinols 5-8 are closely related to four metabolites, namely sorbicillin (1), 2',3'-dihydrosorbicillin (2), vertinolide (3) and bisvertinoquinol (4), previously isolated from the same organism.The entire group (1-8) from V. intertextum is referred to as the vertinoids, which are understood to be hexaketide-derived metabolites with two additional methyl groups, one at C(2) and the other at C(4) (from the carboxylic end) of the C₁₂-chain; 1-3 are monomeric (C₁₄) and 4-8 are dimeric (C₂₈) vertinoids.A scheme is proposed interrelating 1-8 biosynthetically and assigning configurations at several of the chiral centres in 4-8 on the basis of the known (S)-configuration of 3.