New lignans from Anogeissus acuminata with HIV-1 reverse transcriptase inhibitory activity

Anolignan A [1] and anolignan B [3] are new dibenzylbutadiene lignans isolated from Anogeissus acuminata. Compounds 1 and 3 were identified as the active HIV-1 reverse transcriptase (RT) inhibitory constituents of this plant obtained by bioassay-guided fractionation. Compound 3, which was very weakly active when tested alone, showed high activity when combined with 1. The activity of 1 was likewise enhanced in the presence of 3. A concave isobole obtained from a plot of data derived from assays with 1 and 3 in combination indicated their synergistic effects. Another new lignan, anolignan C [5], and a known lignan, (-)-secoisolariciresinol [10], were also isolated from this plant. Compounds 5 and 10 did not have activity against HIV-1 RT. Compounds 1, 3 and 5 were either weakly cytotoxic or noncytotoxic when tested in various cancer cell lines. The structures of 1-5 and 10 were established by spectroscopic methods, especially by 1D and 2D nmr experiments.