Infectious diseases are of ancient origin, and mankind has a venerable history of use of higher plant extracts for the therapy of such infections. Some such agents survive in use from earlier times--quinine, emetine, and sanguinarine, for example--but the modern use of fermentation-based antibiotics has greatly overshadowed work on agents from other sources. After a brief review of the present status of the field of antibiotics, this review focuses upon the present status of antimicrobial agents from higher plants with particular reference to agents from plants with a folkloric reputation for treatment of infections. In particular, recent work on the tropical genus Erythrina is emphasized. The use of modern microbiological techniques demonstrates that higher plants frequently exhibit significant potency against human bacterial and fungal pathogens, that many genera are involved, that many folkloric uses can be rationalized on this basis, that the active constituents are readily isolated by bioassay-directed techniques, that their chemical structures are types uncommon amongst fermentation-based agents but are familiar to natural product chemists, that their antimicrobial spectra are comparatively narrow but that their potency is often reasonable, that they are comparatively easy to synthesize and the unnatural analogues so produced can possess enhanced therapeutic potential and, thus, it is concluded that such work generates a gratifying number of novel lead structures and that the possibility of finding additional agents for human or agricultural use based upon higher plant agents is realistic.

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A new group of alkaloids emerged in 1819 following the isolation of piperine from the fruits of Piper nigrum. Since then, a large number of these compounds now referred to as piperine-type alkaloids or alkamides or piperamides have been isolated commonly from species belonging to the genus piper (piperaceae) which have worldwide geographical distribution. As a result of the traditional uses of piper species as spices in foods and in phytomedicines globally a number of their extractives and indeed the constituent amides have been screened for pharmacological properties. The biogenesis of the amides has been investigated and a number of synthetic pathways have been developed to make them readily available for biological studies. It has now been established that piperine and its analogues are potential pesticides and possess a number of medicinal properties. They are regarded as universal enhancers in pesticide and drug formulations. This review enhances our knowledge of these amides and paves way for further work.

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Examination of bioactive mother-liquors from previous large s c a l e experimnts on the antimicrobial agents from the Nigerian medicinal plant, ENthrira mildbraedii, led t o the isolation and s t r u c t u r a l characterization of two new pterocarpans, erybraedin D and E. Erybraedin D was i n i t i a l l y isolated as its apparently a r t i f a c t u a l hemiethyl phthalate ester. m t h new pterocarpans possess marginal antimicrobial potency in *. The genus ENthrina contains numerous a t t r a c t i v e species distributed i n t r o p i a l and subtropical Extracts of the leaves, bark and r m t s have a significant history of use i n indigenous medical practice for the treatment of various diseases including applications l i k e l y t o include microbial i n f e~t i o n s .~ I n previous studies from t h i s laboratory, we have shown that the roots of many species contain flavanoids, p a r t i c u l a r pterocarpans, .rhich possess s u f f i c i e n t potency innagainst human pathogens t o r a t i o n a l i z e the l c c a l p c p l l a r i t y of extracts a s medicament^.^ Other laboratories have made a n a l q o u s finding^.^ I n particular, we have recently sharn t h a t Ervthrina mildbraedii, c o l l e c t e d i n northern Nigeria, possessed several antimicrobial agents, three new t o the l i t e r a t u r e . These are erythrabyssin-I1 i l l , isoneorautenol (21, and erybraedins A i3), B (41, and C (51.' While examining the mother-liquors from the above study, we detected two q u i t e minor antimicrobial agents which were not identical with the above andwhich proved t o he new to the l i t e r a t u r e . This paper describes t h e i r properties and t h e i r s t r u c t u r a l characterization Erybraedin D hemiethyl phthalate (61 was isolated a s a gum: i r CHC13/max an-' : g, A=-HI, 7.73 IZH, m, Ar-HI; EIMS m/z ( r e l . int., 8 ) : 390 159.21, 375 I l O O ) , 319 03.91, 185

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