New sesquiterpenes from Sonchus transcaspicus

Four new eudesmanolides were isolated from the whole plant of Sonchus transcaspicus and their structures were elucidated by means of spectroscopic methods, including 2D-NMR (¹H-¹H COSY, HMQC, HMBC and NOESY) and NOEDS (NOE difference spectra) as 1β-O-β-D-glucopyranosyl- 5α,6βH-eudesma-3-en-12,6α-olide (1), 1β-O-β-D- glucopyranosyl-15-O-(p-hydroxyphenylacetyl)-5α,6βH-eudesma-3,11(13) -dien-12,6α-olide (2), 1β-O-β-D-glucopyranosyl-(6′-O-p- hydroxyphenyl acetate)-15-O-(p-hydroxyphenylacetyl)-5α,6βH-eudesma-3, 11(13)-dien-12,6α-olide (3) and 1β-hydroxy-15-O-(p- methoxyphenylacetyl)-5α,6βH-eudesma-3,11(13)-dien-12,6α-olide (4). Compounds 1, 2 and 3 showed antibacterial activity against Escherichia coli and Staphylococcus aureus cells. Compounds 2 and 3 were evaluated for their in vitro cytotoxic activity against cultured SMMC-7721 (human hepatoma), HELA (human cervical carcinoma) and B-16 (murine melanoma) cells. The IC₅₀ values for 2 were 108.0, 161.1 and 203.0 μM and those for 3 were 74.1, 117.3 and 135.0 μM, respectively. The structure-activity relationship is discussed.