Natural Product Reports Editorial Board Professor T. J. Simpson (Chairman) University of Bristol Dr C. Abell University of Cambridge Dr J. R. Hanson University of Sussex Dr R. 9.Herbert University of Leeds Professor J. Mann University of Reading Dr D. A. Whiting University of Nottingham Natural Product Reports is a bimonthly journal of critical reviews. It aims to foster progress in the study of bioorganic chemistry by providing regular and comprehensive reviews of the relevant literature published during well-defined periods. Topics include the isolation structure biosynthesis and chemistry of the major groups of natural products -alkaloids terpenoids and steroids aliphatic aromatic and 0-heterocyclic compounds. Many reviews provide details of biological activity and wider aspects of bioorganic chemistry including developments in enzymology genetics and structural spectroscopic and chromatographic methods of general interest to all workers in the area.Articles in Natural Product Reports are commissioned by members of the Editorial Board or accepted by the Chairman for consideration at meetings of the Board. Natural Product Reports (ISSN 0265-0568) is published bimonthly by The Royal Society of Chemistry Thomas Graham House Science Park Milton Road Cambridge CB4 4WF England. 1994 Annual Subscription Price E.C. f266.00 Overseas f286.00 U.S.A. $500.00 Canada f279.00. Change of address and orders with payment in advance to The Royal Society of Chemistry The Distribution Centre Blackhorse Road Letchworth Herts.SG6 1 HN England. Air Freight and mailing in the U.S. by Publications Expediting Service Inc. 200 Meacham Avenue Elmont NY 11003. US Postmaster send address changes to Natural Product Reports Publications Expediting Service Inc. 200 Meacham Avenue Elmont NY 11003. Second-Class postage paid at Jamaica NY 11431-9998. All other despatches outside the U.K. are by Bulk Airmail within Europe anti Accelerated Surface Post outside Europe. Printed in the U.K. 0 The Royal Society of Chemistry 1994 All Rights Reserved No part of this publication may be reproduced stored in a retrieval system or transmitted in any form or by any means electronic mechanical photographic recording or otherwise without the prior permission of the publishers. Printed in Great Britain by the University Press Cambridge Subscription rates for 1994 E.C. f266.00 Overseas f286.00 U.S.A. US $500.00 Subscription rates for back issues are (1 989) (1 990) (1991) (1992) (1993) E.C. f169.00 f 177.00 f198.00 f222.00 f242.00 Overseas f194.00 f204.00 f228.00 f250.00 f266.00 U.S.A. US $388.00 US $398.00 US $467.00 US$474.00 US$532.00 Members of the Royal Society of Chemistry should order the journal from The Membership Manager The Royal Society of Chemistry Thomas Graham House Science Park Milton Road Cambridge CB4 4WF England