Seven new withanolides, salpichrolides O-U (1-7), the known 2,3-dihydrosalpichrolide B (9), a substance not previously isolated from a natural source, and three known compounds, salpichrolide D (8), salpichrolide A (10), and salpichrolide C (11), were isolated and characterized from the aerial parts of Salpichroa origanifolia and S. tristis var. lehmannii. Compounds 1-4 and 8 have an oxygenated D ring, while compounds 5-7 and 9-11 possess a six-membered aromatic D ring. The structures of the isolated compounds were identified by analysis of their spectroscopic data including NMR and MS. Withanolides 1, 3, 8, 10, and 11 exhibited selective radicle growth inhibition toward Lactuca sativa (lettuce) at 150 and 400 ppm.

Incubation of salpichrolide A (1) with Rhizomucor miehei produced hydroxylation in rings B and C (C-7 and C-12) and led to C-5-C-6 epoxide opening, while incubation of salpichrolides C (2) and G (3) with R. miehei led to epoxide opening at the C-24-C-25 and C-5-C-6 positions, respectively. Biotransformation of salpichrolide A (1) with Cunninghamella elegans produced stereoselective hydroxylated, oxidized, and reduced derivatives in different positions of the A, B, and C rings and C-5-C-6 epoxide opening. In addition, selective epoxide opening at the C-5-C-6 or C-24-C-25 positions was obtained from the incubation of salpichrolide A (1) with Curvularia lunata.