Three new 30-norfriedelane and a new friedelane triterpenes from the trunk bark of Caloncoba welwitschii (Oliv.) Gilg (Achariaceae).

Phytochemical investigation of the methanolic extract of the trunk bark of Caloncoba welwitschii (Oliv.) Gilg (Achariaceae) led to the isolation of four new compounds, including three new 30-norfriedelane triterpenes, welwitschiilactones D-F (1-3), one new friedelane triterpene, welwitschioic acid (4) as well as ten known compounds: stigmastane-3,6-dione (7), a mixture of β-sitosterol and stigmasterol (6a and 6b), a mixture of β-sitosterol and stigmasterol glucoside (11a and 11b), (2S,3S,4R,5R)-N-(1,3,4,5-tetrahydroxyndecan-2-yl)tetradecanamide (10), 1-O-β-D-glucopyranosyl-(2S,3R,8E)-2-[(2'R)-2-hydroxylpalmitoylamino]-8-octadecene-1,3-diol (12), 3β,21β-dihydroxy-27-oxo-30-nor-(D:A)-friedo-olean-20(29))en-27,19α-lactone (8), 21β-hydroxy-3,27-dioxo-30-nor-(D:A)-friedo-olean-20(29)-en-27,19α-lactone (9) and 2β,21β-dihydroxy-27-oxo-30-nor-(D:A)-friedo-olean-20(29)-en-27,19α-lactone (5). The structures of all the isolated compounds were determined by extensive spectroscopic analyses (1D and 2D NMR as well as ESI-MS). The relative configuration of the 20-oxymethine in 1 as well as that of 19-oxymethine in 2 and 3 has been established using the NOESY spectrum. In an experiment, a sample of welwitschiilactone C (5) was chemically modified through reduction reaction to give a new hemi-synthetic derivative namely 2β,3β,21β-trihydroxy-30-nor-(D:A)-friedo-olean-20(29)-en-27,19α-lactone (5a).