Chemistry for the Future. Proceedings of the 29th IUPAC Congress, Cologne, Federal Republic of Germany, 5–10 June 1983 PDF
Preview Chemistry for the Future. Proceedings of the 29th IUPAC Congress, Cologne, Federal Republic of Germany, 5–10 June 1983
Some Other IUP AC Titles of Interest from Pergamon Press IUPAC Symposium Series BENOIT & REMPP: Macromolecules BRITTON & GOODWIN: Carotenoid Chemistry and Biochemistry BROWN & DAVIES: Organ-Directed Toxicity — Chemical Indices and Mechanisms CIARDELLI & GIUSTI: Structural Order in Polymers EGAN & WEST: Collaborative Interlaboratory Studies in Chemical Analysis FREIDLINA & SKOROVA: Organic Sulfur Chemistry FUWA: Recent Advances in Analytical Spectroscopy LAIDLER: Frontiers of Chemistry (Proceedings of the 28th IUPAC Congress) MIYAMOTO & KEARNEY: Pesticide Chemistry — Human Welfare and the Environment NOZAKI: Current Trends in Organic Synthesis ST-PIERRE & BROWN: Future Sources of Organic Raw Materials (CHEMRAWN I) SHEMILT: Chemistry and World Food Supplies: The New Frontiers (CHEMRAWN II) TROST & HUTCHINSON: Organic Synthesis — Today and Tomorrow IUPAC Nomenclature Guides IRVING, FREISER & WEST: Compendium of Analytical Nomenclature IUPAC: Nomenclature of Inorganic Chemistry and How to Name an Inorganic Substance (2-part set) RIGAUDY & KLESNEY: Nomenclature of Organic Chemistry WHIFFEN: Manual of Symbols and Terminology for Physicochemical Quantities and Units Other IUPAC Books COETZEE: Recommended Methods for Purification of Solvents and Tests for Impurities KORNHAUSER, RAO & WADDINGTON: Chemical Education in the Seventies Journals CHEMISTRY INTERNATIONAL — IUPAC's international news magazine PURE AND APPLIED CHEMISTRY — IUPAC's official journal, featuring proceedings of IUPAC conferences, nomenclature rules and technical reports INTERNATIONAL UNION OF PURE AND APPLIED CHEMISTRY in conjunction with Gesellschaft Deutscher Chemiker CHEMISTRY FOR THE FUTURE Proceedings of the 29th IUPAC Congress Cologne, Federal Republic of Germany, 5-10 June 1983 Edited by H. GR٢NEWALD Ver Jag Chemie GmbH Weinheim, Federal Republic of Germany PERGAMON PRESS OXFORD · NEW YORK · TORONTO · SYDNEY · PARIS · FRANKFURT U.K. Pergamon Press Ltd., Headington Hill Hall, Oxford 0X3 OBW, England U.S.A. Pergamon Press Inc., Maxwell House, Fairview Park, Elmsford, New York 10523, U.S.A. CANADA Pergamon Press Canada Ltd., Suite 104, 150 Consumers Road, Willowdale, Ontario M2J1P9, Canada AUSTRALIA Pergamon Press (Aust.) Pty. Ltd., P.O. Box 544, Potts Point, N.S.W. 2011, Australia FRANCE Pergamon Press SARL, 24 rue des Ecoles, 75240 Paris, Cedex 05, France FEDERAL REPUBLIC Pergamon Press GmbH, Hammerweg 6, OF GERMANY D-6242 Kronberg-Taunus, Federal Republic of Germany Copyright rt 1984 International Union of Pure and Applied Chemistry AJJ flights Reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means: electronic, electrostatic, magnetic tape, mechanical, photocopying, recording or otherwise, without permission in writing from the copyright holders. First edition 1984 Library of Congress Cataloging in Publication Data IUPAC Congress (29th : 1983 : Cologne, Germany) Chemistry for the future. At head of title: International Union of Pure and Applied Chemistry in conjunction with Gesellschaft Deutscher Chemiker. I. Chemistry—Congresses. I. Gr٧newald, Η. II. International Union of Pure and Applied Chemistry. III. Gesellschaft Deutscher Chemiker. IV. Title. QD1.I95 1983 540 83-23825 British Library Cataloguing in Publication Data International union of pure and Applied Chemistry. Congress f29th : 1983 : Cologne) Chemistry for the future.—(IUPAC symposium series) 1. Chemistry—Congress I. Title II. Gr٧newald, Η III. Gesellschaft Deutscher Chemiker IV. Series 540 QDl ISBN 0-08-029249-6 In order to make this volume available as economically and as rapidly as possible the authors' typescripts have been reproduced in their original forms. This method unfortunately has its typographical limitations but it is hoped that they in no way distract the reader. Printed in Great Britain by A. Wheaton & Co. Ltd., Exeter Scientific Committee President: R. Sammet Secretary General: W. Fritsche Members: Μ. Becke Κ. Η. B٧chel Η. Dφrfel Μ. Eigen Ε. O. Fischer Ε. U. Franck Ο. Glemser Η. Hellmann J. Thesing Ε. Vogel Η. G. Wagner Κ. Weissermel G. Wilke INTERNATIONAL UNION OF PURE AND APPLIED CHEMISTRY IUPAC Secretariat: Bank Court Chambers, 2-3 Pound Way, Cowley Centre, Oxford 0X4 3YF, UK ix CFF-A* PREFACE Chemistry as a science covers a wide spectrum of applications of increasing importance for an ever growing mankind to meet the basic needs regarding food, health, clothing and accommodation. It also plays an important role in world economics. Behind these applications of chemical science which are clearly visible and familiar to the general public lies considerable work in the forefield to which the scientific chemical societies effectively contribute. They promote the transfer of knowledge and experience by several appropriate means. The International Union of Pure and Applied Chemistry is active for that purpose in an international scope; with its incomparable work, including continuing projects which have spanned many decades, it has contributed substantially to the progress of chemistry. One of the most effective means for the transfer of knowledge is undoubtedly the Chemical Congress. The Gesellschaft Deutscher Chemiker (German Chemical Society) on behalf of the National Adhering Organization Deutscher Zentralausschuss fόr Chemie readily took over the preparation and organization of the 29th IUPAC Congress which successfully took place from the 5th to the 10th of June 1983 in the Congress Centre in Cologne. The programme consisted of 9 invited plenary lectures and 52 invited section main lectures by prominent scientists as well as 160 discussion papers and 242 posters of high scientific level. They covered New Advances in Inorganic Chemistry, in Organic Chemistry, and in Physical and Theoretical Chemistry, Progress in the Production of Chemical Basic Materials, Education in Chemistry, and a Joint Symposium on Chemical Information. The scientific world is grateful to Pergamon Press for taking over the task of publishing the plenary and section main lectures of the 29th IUPAC Congress in one representative volume in order to disseminate them beyond the Congress participants from 36 countries, and provide a lasting documentation of the results of this major international event in chemical science. Wolfgang Fritsche Secretary General, Gesellschaft Deutscher Chemiker Secretary General, 29th IUPAC Congress xi HOST-GUEST COMPLEXATION CHEMISTRY Donald J. Cram Department of Chemistry, University of California at Los Angeles, Los Angeles, California 90024 USA Abstract - The principles of complementarity and of preorganizaron have been applied to the study of structural recognition in complexation. A chiral host has been synthesized which by design complexes enantiomers of a particular configuration of racemic amino acid or ester salts by selec tivity factors as high as 31. The same host catalyzes (with turnover) the reaction with an electrophile of a complexed prochiral potassium- carbon acid salt to produce a chiral product that is ^99% optically pure. A mimic for the acylation of a serine esterase has been synthesized which by collection and orientation of reactants accelerates a transacylation rate by a factor of 10 11 over that observed for a noncomplexing model compound. A host containing an enforced cavity lined with electron pairs (a spherand) is reported which is the strongest known complexer of lithium and sodium ions. This ligand system rejects all other metal ions. Organization of this host during synthesis rather than during com plexation is shown to enhance binding by factors as high as > 10 12. Hosts with enforced concave surfaces of molecular dimensions (cavitands) have been prepared. Cell-like hosts have been designed that are potentially capable of encapsulating organic molecules. The hosts and complexes were designed with the help of scale molecular models, and their structures confirmed with crystal structure and nuclear magnetic resonance spectral techniques. INTRODUCTION The magnificent ability of genes, enzymes, immune systems, hormones, and pheromones to interconvert organic compounds and regulate chemical traffic in organisms depends on struc tural recognition in complexation. The receptors and substrates of evolutionary origin provide the organic chemist with both inspiration and challenge to design and synthesize organic compounds which through structural recognition in complexation might perform chemi cal tasks never before carried out by compounds of nonevolutionary origin. Hosts, the synthetic counterparts of biological receptors, are conveniently defined as organic compounds containing convergently arranged binding sites. Guests, the synthetic counterparts of substrates, possess divergently arranged binding sites. Host-guest com plexes are formed when the molecular shapes and binding sites of hosts and guests are complementary. A complex is composed of a host and guest held together in a definite structural relationship. The binding partners are attracted by hydrogen bonding, ion- pairing, ion-dipole, pi-acid to pi-base, van der Waals forces, and by solvent liberation phenomena (in water solution, hydrophobic binding). These forces are weak compared to the strength of covalent bonds, so multiple contacts of binding sites of hosts and guests are needed to structure most complexes. Structural recognition in complexation depends upon unique complementary relationships between potential complexing partners. Complementarity has geometric and electronic features, both of which are subject to design when the host and guest are organic compounds. Relationships between the binding free energies of complexes and the structures of the complexing partners are now subject to systematic examination and rationalization. This paper addresses the following questions. Can chiral hosts be designed and synthesized to complex only one enantiomer of a racemate? Can chiral hosts be used to catalyze re actions that lead from prochiral starting materials to enantiomerically pure products? Can hosts be designed that mimic some of the catalytic features of the serine esterases? Can hosts be designed that show very high discrimination in complexing alkali metal ions? What are the relationships between the free energies of binding of host to guest and the degree to which each is conformationally organized for complexing prior to complex formation? 3 4 D. J. Cram Can hosts with rigid concave surfaces of molecular dimensions be prepared? Can cell-like hosts be designed that might encapsulate organic guests? CHIRAL RECOGNITION IN COMPLEXATION Scale molecular model examination suggested that chiral host ]_ and guest 2 should form complex 3. The complex was synthesized, and its crystal structure 4 turned out to possess the anticipated structure (Ref. 1). Host RR-5 was prepared, since molecular model exami nation suggested it should complex D-amino acid and ester salts, e.g., D-6, better than their L-anantiomers. Thus 1_ should be the more stable complex. Solutions of racemic amino acid and ester salts in water were extracted with chloroform solutions of RR-5, and the layers were separated. The optical purity and configuration of the guest isolated from each layer were determined. From the values obtained, the distribution constants for each enantiomer were determined, as well as the differences in free energies of the diastereo- meric complexes. Twelve different amino acids or esters were examined. In all cases, guests of the D-configuration were the more complexed enantiomers by factors that ranged from a high of 31 to a low of 2. The -Δ(Δ6°) values ranged from a high of 1.9 to a low of 0.4 kcal mol"1. The highest chiral recognition was observed with phenylglycine methyl ester hexafluorophosphate salt (Ref. 2). An amino acid (or ester) resolving machine based on a W-tube was designed, built, and run continuously for several days. The resolution is based on chiral recognition of each enantiomer in ion transport through bulk liquid membranes (Fig. 1). The two enantiomers of about 90% optical purity were obtained from this experi ment as applied to phenylglycine methyl ester hexafluorophosphate salt. CH 3 2 3 4 R 5 l + H-N--H Η PFef 6 7 Host-Guest Complexation Chemistry RESOLVING MACHINE Fig. 1 Amino acid and amino ester resolving machine CHIRAL CATALYSIS Chiral host RR-5> was also used as a turnover catalyst in the conversion of prochiral salt 8 as guest into chiral S-9 of about 99% optical purity. The catalyst turnover number was 10, and the value for A(AG+T was ^2.0 kcal mol" 1. Formula iEMs a schematic representation show ing the charge and aryl group location in the plane of 8. This guest uniquely fits into host 5^ to produce complex ]J0. In the complex, 8^_ is "sided" and the electrophile, 3-pentenone, approaches the carbanion only from the open side. The direction of the con- figurational bias was predicted in advance of experiment through molecular model examination (Ref. 4). 8' 10 6 D. J. Cram PROGRESS TOWARD A SERINE ESTERASE MIMIC Formula Y\_ represents the important components in the active sites of serine esterase enzymes. Elucidations of their crystal structures inspired the design with the help of molecular models of target host 12. We predict that 12 will catalyze the hydrolysis of guests such as 13, and possibly amides as well. Proton transfer catalyst 11 In an incremental approach to 12, we synthesized host 14, and found that it complexed Jj5 (as a picrate) in chloroform with a binding free energy of -AG° = 13.2 kcal mol .l Two views of the crystal structure of the complex 16 are shown in 17 and 18. The nucleophilic primary hydroxyl group was introduced into the system by synthesizing 19. This host com plexed methyl ammonium and sodium picrates in chloroform with 12.7 and 13.6 kcal mol" 1 binding free energy, respectively (Ref. 5). Host J_9 was acylated by 20 to give complexed ester 21 and £-nitrophenol. The kinetics of formation of 21 were measured in chloroform and found to be first order in added RaN^NHClOi, buffer ratio. Thus the alkoxide ion is the nucleophile. The rate of acylation of 19 was MO 11 faster than the rate for the non- complexing model compound, 3-phenylbenzyl alcohol. However, when sodium Perchlorate was added, the acylation rate of ]_9 was inhibited by several powers of 10. Thus the acylation of 1_9, like that of serine esterases, is subject to competitive inhibition. These facts demonstrate that collecting and orienting reactants through highly structured complexation results in enormous rate acceleration. We anticipate that incorporation of the imidazole and carboxylate groups as in target catalyst ]_2 will induce hydrolysis of acylated esters and provide the catalyst turnover characteristic of enzymes (Ref. 6). The synthesis of 12 has not yet been accomplished. Nucleophile Proton transfer 12 13 CDCI 3] 25° 1 14 15 16 Host-Guest Complexation Chemistry 7 SPHERANDS AND THE PRINCIPLE OF PREORGANIZATION Crystal structures of chorands (crowns) and cryptands show that they fold to fill their own cavities (Ref. 1). Their complexation involves conformational reorganization and desolva- tion of their binding sites. To assess the cost in binding free energy of guest organizing and desolvating host, we designed and synthesized the spherands whose binding sites are rigidly preorganized and shielded from solvation by a hydrocarbon shell. Their binding free energies were then compared to conformationally mobile systems. The crystal structure of prototypical spherand 22 is shown in 23. Those of their lithium and sodium ion complexes are pictured in 2£ and 25. Notice that 22 has the rare property of containing a hole defined by octahedrally-arranged oxygens whose twenty-four unshared electrons define the boundaries of the hole. The hole is shielded from solvation by the supporting aryl groups and the six methyl groups attached to the oxygens (Ref. 7).
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