Casearia membranacea Hance (Flacourtiaceae) is a tree found in the northern region of Taiwan. Bioassay-directed fractionation of the MeOH-layer has resulted in the isolation of six new clerodane diterpenes, Caseamembrins A-F (1-6) along with a known compound, rel-(2S,5R,6R, 8S,9S,10R,18S,19R)-diacetoxy-18,19-epoxy-6-hydroxy-2-(2-methylbut- anoyloxy)cleroda-3,13(16),14-triene (7). The structures of compounds 1-6 were determined by the physical methods such as IR¡Bmass¡Boptical rotation, 1D¡B2D NMR spectral analysis, and the published reports about the data of related compounds . The spectral data of 1-6 are in conformity with the basic skeleton of clerodane diterpenes previously isolated from Casearia membranacea Hance.. The basic structures of 1-6 contain two 6-membred ring linked with six carbon diene side chain at C-9 and two ester carbonyl functional groups at C-2 and C-18 respetirely. Compound 1 had an ester carbonyl at C-2 position, with an acetoxyl and a hydroxyl group at C-19/6 position, the structure of 1 was assigned as rel-(2S,5R,6R,8S,9S,10R,18S,19R)-18-butanoyloxy-19-acetoxy-18,19 -epoxy-6-hydroxy-2-(2-methylbutanoyloxy)cleroda-3,13(16),14-triene (Caseamembrin A). Compound 2 had a methoxyl group at C-18 position, that 2 has the structure of rel-(2S,5R,6R,8S,9S,10R,18S,19R)-18-methoxy -19-acetoxy-18,19-epoxy-6-hydroxy-2-(2-methylbutanoyloxy)cleroda-3,13(16),14-triene (Caseambrin B). Compound 3 had an acetoxyl at C-19 position, and two hydroxyl group at C-6/7. Compound 3 was assigned the structure of rel-(2S,5R,6R,7R,8S,9S,10R,18S,19R)-18-butanoyloxy-19- acetoxy-18,19-epoxy-6,7-dihydroxy-2-(2-methylbutanoyloxy)cleroda-3, 13(16),14- triene (Caseamembrin C). Compound 4 had two acetoxyl at C-7/19 and hydroxyl group at C-6, the assignment of its structure as rel-(2S,5R,6S,7R,8S,9S,10R,18S,19R)-18-butanoyloxy-19-acetoxy -18,19-epoxy-6-hydroxy-7-acetoxy-2-(2-methylbutanoyloxy)cleroda-3,13(16),14- triene (Caseamembrin D). Compound 5 had two acetoxyl at C-18/19 position, and a hydroxyl group at C-6 position. 5 was established as rel-(2S,5R,6R,8S,9S,10R,18S,19R)-18,19-diacetoxy-18,19-epoxy-6- hydroxy-2-(2-methylbutanoyloxy)cleroda-3,13(16),14-triene (Caseamembrin E). Compound 6 had a hydroxyl group at C-6 position and it was deduced that the C-18/19 acetal ring was opened thus forming the two aldehydic units. The structure of 6 was established as rel-(2S,5R,6R,7R,8S,9S,10R,18S,19R)-6-hydroxy-2-(2-methylbutanoyloy) cleroda-3,13(16),14-triene-18,19-dicarboxyaldehyde (Caseamembrin F). It is worthy to mention that this is the first report of the isolation of 1-6 from a natural source. In a preliminary pharmacological aporach (cytotoxicity), compounds 1-6 exhibited moderate cytotoxicity against (NUGC-3) and (HONE-1) cancer cells with IC50 0~1¢Mvalues at 20mg/ml.

ABSTRACT The Genus Casearia is a rich source of cleordane - type diterpenes. To search for practical sources of potential cleordane - type diterpenes, and to study the structure and activity relationship of cleordane - type diterpenes, the twigs and leaves of Casearia membranacea Hance ( Flacourtiaceae ) was collected for phytochemical and anti-tumor investigation. Bioassay-directed fractionation of an ethyl acetate layer of Casearia membranacea has resulted in the isolation of six new clerodane-type diterpenes. The structures of these cleordane-type diterpenes were established and designated as Caseamembrins G¡ãL¡]1¡ã6¡^and their derivatives compounds 7 and 8. The structures of compounds 1¡ã8 were determined by application of NMR techniques included 1H NMR, 13C NMR, DEPT, COSY, HMQC, HMBC, NOESY and another physical methods which include MS, UV, IR and optical rotation, and the published reports about the data of related compounds. The spectral data of 1¡ã8 are in conformity with the basic skeleton of cleordane-type diterpenes previously isolated from Casearia membranacea Hance. The basic structures of 1¡ã8 contain two 6- menbered ring. The structures were identified as rel-(2S,5R,6R,8S,9S,10R, 18S,19R)-2-hydroxy-6-butanoyloxy-18,19-acetyloxy-18,19-epoxy-cleroda-3,13(16),14-triene (Caseamembrin G, 1¡^¡Brel-(2S,5R,6R,8S,9S,10R,18S, 19R)-2-hydroxy-6,18-dibutanoyloxy-19-acetyloxy-18,19-epoxy-cleroda -3,13(16),14-triene (Caseamembrin H, 2¡^¡Brel-(2S,5R,6R,8S,9S,10R,18S ,19R)-2-(2-methylbutanoyloxy)-6-hydroxy-18-methoxy-19-acetyloxy-18,19-epoxy-cleroda-3,13(16),14-triene¡]Caseamembrin I, 3¡^¡Brel-(2R,5R ,6R,8S,9S,10R)-2-(2-methylbutanoyloxy)-6-hydroxy-cleroda-3,13(16),14 -triene-18,19-dicarboxaldehyde ( Caseamembrin J, 4¡^¡Brel-(2S,5R,6R,7R, 8S,9S,10R)-2,7-diacetyloxy-6-hydroxy-cleroda-3,13(16),14-triene-18,19-dicarboxaldehyde¡]Caseamembrin K, 5¡^¡Brel-(2S,5R,6S,7R,8S,9S,10R, 18S,19R)-2-butanoyloxy-6,7-dihydroxy-18-butanoyloxy-19-acetyloxy-18,19-epoxy-cleroda-3,13(16),14-triene¡]Caseamembrin L, 6¡^¡A¤Îrel-(2S,5R ,6R,8S,9S,10R,18S,19R)-2-O-acetyl-6-butanoyloxy-18,19-acetyloxy-18,19-epoxy-cleroda-3,13(16),14-triene ( 7¡^¡Brel-(2S,5R,6R,8S,9S,10R,18S,19 R)-2-O-acetyl-6,18-dibutanoyloxy-19-acetyloxy-18,19-epoxy-cleroda-3,13(16),14-triene¡]8¡^. It is worthy to mention that this is the first report of the isolation of 1¡Ð6 from a natural source and their derivatives compounds 7 and 8. Compound 1 exhibited moderate cytotoxicity against¡]Hepa59T/VGH¡^ ,¡]KB¡^and ¡]Hela¡^cancer cells , but compound 3 and 4¡B5 show no activity against those cancer cell lines.