| Summary: | A study of the secondary metabolism of two northeastern Pacific sponges and two Sri Lankan nudibranchs has led to the isolation of thirteen new and one previously known natural products. The structures of all of the compounds were determined by a combination of spectroscopic data analysis and chemical interconversions.
A study of the chemistry of the northeastern Pacific sponge Hexadella sp. has resulted in the isolation of six new brominated alkaloids. Two of these, hexadellins A (77) and B (78), are derived from dibromotyrosine. The structures of compounds 77 and 78 were determined via their acetylated derivatives 79 and 80. Four compounds possessing novel bis(indole) structures have also been isolated. Topsentin B2 (74) was isolated as a mixture of two slowly interconverting tautomers, 74a and 74b. Methylation of 74 resulted in the production of trimethyltopsentin B2 (75); the structure of 75 was determined spectroscopically. The structures of dragmacidons A (81), B (82), and C (83) were determined by a combination of spectral data interpretation and chemical interconversions. Dragmacidon C (83) was originally incorrectly assigned as 88; the correct structure was determined based upon synthesis of the model compound 94. Compounds 77 and 78 possess antimicrobial activities. Compounds 74 and 81 show considerable cytotoxic and antineoplastic activities.
Five new triterpene glycosides have been isolated from the northeastern Pacific sponge Xestospongia vanilla. The structures of isoxestovanin A (125), xestovanin C (127), dehydroxestovanin A (129), epi-dehydroxestovanin A (131), and dehydroxestovanin C (132) were all determined by a combination of spectral data interpretation and chemical interconversions. These compounds all contain the deoxy sugars L-rhamnose and D-fucose. Isoxestovanin A (125) possesses a new carbon skeleton and xestovanin C (127) and dehydroxestovanin C (132) possess linear
trisaccharide fragments which have not been previously encountered in triterpene
glycosides isolated from X. vanilla.
The Sri Lankan nudibranch Chromodoris glenei has yielded the known compound 12-desacetoxyshahamin C (153) and the new metabolite shahamin K (155). Both compounds possess dendrillane diterpene skeletons. The compound chromodorolide B (156) was isolated from specimens of Chromodoris cavae. It is only the second known diterpene natural product possessing the chromodorane skeleton. === Science, Faculty of === Chemistry, Department of === Graduate
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