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Nine labdane type diterpenes isolated from the plant Cistus creticus subsp. creticus and from the resin "Ladano" which is excreted on the surface of the leaves and stems of this plant, were examined for their in vitro cytotoxic activity against 14 human leukemic cell lines. Compound 1, (13E)-labd-13-ene-8 alpha,15-diol, exhibited cytotoxic activity against 13 of the cell lines tested, while compound 2, (13E)-labd-7,13-dienol, was active only against HL60 cells. Further compound 1 was examined for its effect on the uptake of [3H]-thymidine as a marker of DNA synthesis.

Two labdane type diterpenes, labd-13(E)-ene,-8alpha,15-diol (1) and labd-13(E)-ene,-8alpha,15-yl acetate (2) were isolated from the hexane extract of Cistus creticus subsp. eriocephalus (Viv.) Greuter & Burdet leaves, while (+)-19-acetoxy-cis-clerodan-3-en-15-oic acid (3) was isolated from the hexane extract of Cistus monspeliensis L. leaves. The compounds were examined for their in vitro cytostatic and cytotoxic activity against nine human leukemic cell lines, three of which exhibited a multidrug resistant phenotype. They were also evaluated for their anti-inflammatory activity in vivo on the back of hairless mice. The cytostatic and cytotoxic activity of the tested diterpenes followed the order 1>2>3. Topical application of the diterpenes on barrier disrupted skin did not seem to have a significant contribution to the repair rate of the skin barrier.

Ten sesquiterpene lactones, 8alpha-O-(3,4-dihydroxy-2-methylenebutanoyloxy)sonchucarpolide (4-epi-malacitanolide) (1), 8alpha-O-(4-acetoxy-2-hydroxymethylbuten-2-oyloxy)-4-epi-sonchucarpolide (2), malacitanolide (3), its 4'-acetyl derivative (4), 8alpha-O-(3,4-dihydroxy-2-methylenebutanoyloxy)dehydromelitensine (5), 8alpha-O-(3,4-dihydroxy-2-methylenebutanoyloxy)-15-oxo-5,7alphaH,6betaH-eleman-1,3,11(13)-trien-6,12-olide (6), the germacranolides 8alpha-O-(4-acetoxy-2-hydroxymethylbuten-2-oyloxy)salonitenolide (7), cnicin (8), and 4'-acetylcnicin (9), and the sesquiterpene methyl 8alpha-O-(3,4-dihydroxy-2-methylenebutanoyloxy)-6alpha,15-dihydroxyelema-1,3,11(13)-trien-12-oate (10), were isolated from the aerial parts of Centaurea spinosa. Nine known flavonoids were also isolated. The structures and the stereochemistry of the new compounds 1 and 2 were deduced by spectroscopic methods. The in vitro activity of 1-10 against three Gram-positive and three Gram-negative bacteria was evaluated using a microdilution method, and their in vitro cytotoxic activity was determined against a panel of human tumor cell lines.