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).
Keywords: 30-norfriedelane triterpene lactone; Caloncoba welwitschii; chemical reduction; friedelane.