Studies on the Chemistry of Australia's Native Fauna and Flora
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Studies on the chemistry of Australia's native flora and fauna My first involvement in natural products chemistry was during my Honours year in chemistry at UNSW in 1964 where, like so many other chemists before me, I set to work on my bag of sawdust obtained from some Australian tree to find out what organic compounds could be extracted from it. The species involved was Sophora tomentosa and under the supervision of Associate Professor Ron Eade I obtained some isoflavone and pterocarpin derivatives. That experience whetted my interest in the chemicals contained living systems and sparked an interest in why they were there. Sophora tomentosa is a member of the Leguminosae and it is only within this family that isoflavones had been found. The work described in this thesis has been carried out at the School of Chemistry, University of New South Wales over a period of, approximately, 25 years. During this time at the University I have been responsible for providing the routine mass specti'ometry service within the School of Chemistry, though the work described herein is not part of that work. GC/MS was initiated within the School in 1969. In 1970, as a postdoctoral fellow, I used the technique for the first time in the my work on insect chemistry. After a period of 5 years at Monash University I returned to UNSW in 1976 to run the routine mass spectrometry service. My involvement with insect chemistry continued and several years later I commenced work on essential oils chemistry. Like a lot of other people who spend their lives in doing chemical research, I got into essential oils research more or less by accident, though in my case this accident was once removed. In my case the route to essential oils was via insect chemistry. This was an area that was very challenging and enjoyable and one in which I was able to make some significant contributions. Professor Ken Cavill was head of the Department of Organic Chemistry at UNSW in the 1960's and 1970's. His research interests at the time were in the area of insect chemistry. Professor Cavill's group at UNSW was interested in the chemistry of the volatile secretions of Australian ants and this is the area in which I was involved, both during the time I spent as a research fellow and postdoctoral associate with him. Afterwards, while running the routine mass spectrometry service at the University of New South Wales I made some contributions in this area. My first contributions had been earlier, however, when as a postgraduate student I had helped collect, by the thousand, the Australian bull ant Myrmecia gulosa (a task not for the faint heaited). Page 1 My first contribution to insect chemistry was an investigation of the volatile hydi-ocarbons of the formicine ant Camponotus intrepidus where we found the 4-methyl alkane series for the first time in arthropods [24]. The references are listed at the end of this introduction and aie contained in the body of the thesis. Fuither work in this area was directed primarily into the two subfamilies Dolichoderinae, in which Professor Cavill was primarily interested, and Ponerinae (in which my interest was increasing). In the Dolichoderinae we made contributions to the knowledge of the chemistry of Iridomyrmex nitidiceps [25], /. purpureas [26], the cuticular hydrocarbons of I. humilis, I. purpureiis and /. nitidiceps [27]. Later on, with Professor Clezy and Dr Phyllis Robertson, we determined the structure of some secondary amines isolated from the venom gland of the dolichoderine ant Technomyrmex albipes [28]. The compounds were synthesised by Mr Chris Leung. This was unusual chemistry as amines had not been isolated from the venom gland of ants of this sub-family before The work in the field of dolichoderine chemistry also led to work on the Fijian stick insect, Graejfae crouani [29], where Mr Noel Davies and myself determined its defensive secretion. The secretion was supplied by Dr Roger Smith at that time of the University of the South Pacific. We also designed an efficient apparatus for collection of crawling insects [30]. My own interest in ants was in the more primitive subfamily Ponerineae and in paiticular the pyrazines that they contained in their mandibular glands. We also found them in the formicine ant Notoncus ectatommoides [31]. The majority of work on ponerine ants in which I was involved was on the genus Rhytidiponera, a wide ranging genus in Australia. We were able to demonstrate the presence of 2,5-dimethyl-3-isopentyl pyrazine in a series of Rhytidoponera species [32,33,34] as well a further pyrazine from the head of the bull ant Myrmecia gulosa [35]. Work of which I am particularly satisfied is that on the secretions of Rhytidoponera metallica in which we found twelve pyrazines, a record for the time, and were able to suggest structures for ten of these compounds which were subsequentiy synthesised by Drs Berhane Tecle and Chang-Ming Sun under the direction of Dr Robert Toia [34]. The remaining two oxygenated pyrazines contained in this ant still await structural elucidation. Later we were able to demonstrate that the E- and Z- isomers of these pyrazines gave different mass spectra, presumably due to steric effects, a featui'e exceptionally raie in mass specti'ometiy [36]. This research led to biosynthetic studies on some of the aromatic compounds contained in the gasters of tliese ponerine ants by students of Dr Robert Toia. My conuibution to this work were in the determination of the structures in question [37,38]. I was also involved in determination of the compounds present in the dolichoderine ml Iridomyrmex discors [39]. Page 2 As a consequence of my interest in pyrazines from natural sources I have been able to contiibute reviews on naturally occurring pyrazines and their mass specti-al characterisation (with Prof. Cavill) [40] and later a review on the pyrazines obtained from insect sources [41]. Contributions to the area of mass spectrometry which I have made over the years include showing that reductions of nitro compounds can take place in the CI source of a mass spectrometer [8], study of the EI and CI mass spectra of aryl ureas [9], contributions to the study of low energy, low temperature mass spectra [10,11,12] and publication of new mass spectra of 2,2-disubstituted benzodioxoles [13], aryl sulphenamides [14] and the rare naturally occun ing p-triketones [15]. I contiibuted as part of a team which used microprocessors to contiol mass spectrometers (when microprocessors were in their infancy) [16, 17], perfected a method of obtaining elemental compositions from low resolution mass spectrometers [18] and demonstrated one of the first LC/MS systems in the world, certainly the first in Australia [19]. Published work on synthetic chemistry includes studies in organophosphorus chemistry (for my Ph. D. under Assoc. Professor Michael Gallagher) [1-7], a synthesis of aryl cyclopropanol derivatives (postdoctoral work with Professor Garry Griffin) [20] and my subsequent further work on these systems [21], the synthesis of 3-arylbenzothiophenes [22] and a minor contribution in pyrrole chemistry [23]. The papers in this and the preceding three paiagraphs[l-23] do not form part of this thesis. The main part of the work submitted for the degree, in which I was the senior author or an equal participant, concems my work on the essential oils of Australian native flora. Australia is blessed with a vast variety of native flora and fauna, throughout the continent. A chemist interested in the volatiles of the native flora is almost overwhelmed with the large number of families present on this continent which contain volatile oils in their leaves, wood, bark and roots. The research in which I have been involved has been mainly undertaken in the family Myrtaceae, which contains two subfamilies, Leptospermoideae and Myrtoideae. This is not surprising as this is the largest oil bearing family, containing over 140 genera in two sub- families. My work in this area is listed in the Table 2. Quite a significant number of species from both sub-families have been investigated and where possible conclusions about their chemotaxonomy have been reached. Work on other families has also been carried out and this is also included in this thesis. The families are described in alphabetical order in the following sections and Table 2. Page 3 The sub-family Leptospermoideae contains many of the large genera within the Myrtaceae, ie. Eucalyptus, Melaleuca, Callistemon and Leptospermum, as well as many other smaller genera. This sub-family is well represented in AustraUa. The other sub-family, Myrtoideae, is not so strongly represented within the Australian region. Within this sub-family, though with the exception of Syzygium, a significant number of genera with the major ones being Austromyrtus, Rhodamnia, Rhodomyrtus, Uromyrtus, Archirhodomyrtus, have been investigated, the vast majority being examined for the first time. Table 1, adapted from Briggs and Johnson and also Wrigley and Fagg 1993, below, gives the major divisions of the Myrtaceae and includes the genera which occur in Australia, while Figure 1 shows the major divisions within the eucalyptus alliance. A summary of the genera on which work has been published is given in Table 2 and the results of this work ai'e briefly discussed in the text following this table. Table 1 Major Divisions of the Myrtaceae Subamily Taxa: Distribution Aust. genera LEFTTOSIPEIRMOIIIIDIEAIE 85:42 SE Asia, Australia, Pacific, outliners in S Africa and Chilie 1 METROSIDEROS 29:11 Pacific, Malesia, N. & E. Austraia ALLIANCE i. Kania suballiance (4):1 Lyscicarpus ii. Meterosideros suballiance (11):3 Metrosideros, Tristania, m.Xanthostemon suballiance (3):1 Xanthostemon Lindsayomyrtus, Tristaniopsis, iv.