Alkaloids from an ascidian and two bryozoans from Tasmania

Detailed chemical examination of the alkaloid content of an ascidian (Clavelina cylindrica) and two bryozoans (Bugula dentata and Hincksinoflustra denticulata) have been undertaken. A total of 21 alkaloids were obtained of which 18 were novel. Two new classes of pyrroloquinoline (cylindricines A, C, D, E, F, G, H, I, K) and pyridoquinoline alkaloids (cylindricines B, J) have been isolated from the ascidian Clavelina cylindrica. This is the first time that the pyridoquinoline ring system has been obtained as a natural product or a synthetic compound, while this is the first occasion that the pyrroloquinoline ring system has been discovered in nature. All together a total of 12 alkaloids were isolated from this ascidian, 11 of them (cylindricines A-K) are novel alkaloids and one (wakayin chloride) had been described previously from another ascidian. Cylindricines A and B, are readily interconvertible via a ring opening closing reaction and a mechanism has been proposed to account for this. Cylindricines F, G, and H are thiocyanates, and cylindricines I and J are isothiocyanates, the first known from an ascidian. Spectroscopic and chemical evidence for the structures of the 12 alkaloids are presented. X-ray crystallographic studies confirmed the structures of two of them (cylindricines A and B), and established the relative stereochemistry, chemical transformations and computer modelling were also used to confirm some of the structures... Six alkaloids belonging to the tambjamine class (tambjamines C, E, G, H, I, J) were obtained from the bryozoan Bugula dentata. Four of them (tambjamines G, H, I, J) are novel alkaloids while two of them .had been described previously from an ascidian and a bryozoan (tambjamines C, E). Spectroscopic and chemical evidence for the structures of the 6 alkaloids are presented... From the bryozoan Hincksinoflustra denticulata three new alkaloids have been isolated. Hinckorfordines A and B both possess the same 1H-azepino[4,5- o]quinindoline new ring system. The structure of hinckorfordine A was determined by spectroscopy and confirmed by an x-ray crystallographic study. The structures of hinckorfordine B and hinckdentine B were elucidated by comparison of the spectral data with those of hinckorfordine A and hinckdentine A.