title: Xylocarpins A and B, two new mexicanolides from the seeds of a Chinese mangrove Xylocarpus granatum: NMR investigation in mixture.
abstract: Xylocarpins A and B, two new mexicanolides with a tiglate group at C-3, have been identified in the mixture using NMR spectroscopy. Both compounds were isolated in the mixture from the seeds of a Chinese mangrove Xylocarpus granatum. The first complete assignments of 1H and 13C NMR data for these mexicanolides were achieved by means of 2D NMR techniques, including 1H-1H COSY, HSQC, HMBC and NOESY spectra. In order to separate xylocarpins A (1) and B (2) by chemical method, the mixture of two compounds was reduced with sodium borohydride in anhydrous methanol. However, the reduction led to the opening of the delta-lactone ring in xylocarpin B and afforded compound 3 as the main product. The complete NMR assignments of compound 3 were also achieved by means of the above 2D NMR techniques. Moreover, xylocarpin A was easily transformed into xylocarpin B during our normal liquid column chromatography. From this point of view, xylocarpin A was deemed to be the genuine natural product and xylocarpin B might be an artifact.
authors.affiliation: Guangdong Key Laboratory of Marine Materia Medica, South China Sea Institute of Oceanology, Chinese Academy of Sciences, 164 West Xingang Road, Guangzhou 510301, P.R. China.
authors.forename: Minyi
authors.initials: M
authors.lastname: Li
authors.forename: Jun
authors.initials: J
authors.lastname: Wu
authors.forename: Si
authors.initials: S
authors.lastname: Zhang
authors.forename: Qiang
authors.initials: Q
authors.lastname: Xiao
authors.forename: Qingxin
authors.initials: Q
authors.lastname: Li
mesh_terms: D001688:Biological Products / Q000737:chemistry; D002247:Carbon Isotopes; D009682:Magnetic Resonance Spectroscopy; D043982:Rhizophoraceae / Q000737:chemistry*; D012639:Seeds / Q000737:chemistry; D014315:Triterpenes / Q000737:chemistry*
chemical_list: D001688:Biological Products; D002247:Carbon Isotopes; D014315:Triterpenes; C523655:xylocarpin A; C523656:xylocarpin B