The alkaloids of some Australian and New Guinea plants

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Summons, Roger Everett
Department of Chemistry
thesis / dissertation description
Four plants belonging to three genera, Cinnamomum (Lauraceae), Mitrella (Annonaceae) and Marsdenia (Asclepiadaceae), have been examined and their main alkaloid constituents identified.The bark of an unnamed New Guinea Cinnamomum species, designated by the herbarium voucher number T.G.H. 13,077, yielded two new 1-benzyltetrahydroisoquinoline alkaloids, cinnamolaurine and norcinnamolaurine, together with the known alkaloids corydine, norisocorydine and reticuline. The leaves of the same species were found to contain corydine and reticuline as the major constituents together with traces of cinnamolaurine. Camphor was identified as a neutral component of the leaves.The structure 1-(41 -hydroxybenzyl)-6,7-methylenedioxy- 2-methyl-1,2,3,4-tetrahydroisoquinoline was assigned to cinnamolaurine on the basis of spectroscopic evidence and this was confirmed by synthesis of the racemate. The structure of norcinnamolaurine was deduced from spectroscopic evidence and was confirmed by the formation of cinnamolaurine on N-methylation and also by synthesis of its racemate. Both cinnamolaurine and norcinnamolaurine were shown to belong to the D series of benzylisoquinoline alkaloids.Cinnamomum laubattii F. Muell, a Queensland species, was found to contain reticuline as the only major alkaloid. This may be of chemotaxonomic interest since C. camphora, the only other species of the genus which has been examined for alkaloids, also yielded reticuline as a major constituent.Mitrella kentii (B1.) Miq., a New Guinea species belonging to the family Annonaceae, appears to be the first of its genus to be investigated for alkaloids. The known compounds anonaine, asimilobine and liriodenine were identified as the main constituents while a minor one was shown to be 3,9-dihydroxy-2,10-dimethoxytetrahydroprotoberberine, a structure that has not been reported previously.Marsdenia rostrata R.Br., the fourth plant studied, originated from two different collection localities. A sample obtained from the Toonumbar State Forest in Northern N.S.W. was found to contain the known alkaloid anabasine and a new basic ester aglycone which has been identified as a mixture of O-acetyl-O-nicotinoyl sarcostin and the corresponding 5α-dihydrosarcostin derivative. A sample collected from the South Coast of N.S.W. yielded the above ester aglycone mixture and a number of neutral pregnane aglycones, one of which has been tentatively identified as metaplexigenin.