INTRODUCTION

The Seventeenth International Symposium on Macrocyclic Chemistry (XVII ISMC) was held in Provo, Utah, U.S.A. on 9 through 14 August 1992. The symposium was partly sponsored by the international union of pure and applied chemistry (IUPAC). The previous five symposia had been held in Hiroshima, Japan (1987); Hamburg, Germany (1988); Townsville, Australia (1989); Odessa USSR (1990); and Sheffield, England (1991). Provo had about 240 participants representing 26 different nations. Out of these about half were from outside the United States of America. Japan had 12 representatives. There were one special award presentation, seven plenary lectures, 33 invited lectures, 15 short oral presentations, and 124 poster presentations. Some of the topics were:

This report focuses on the lectures presented by the chemists from the United States of America and Japan.

BACKGROUND

Since the discovery of crown ethers by C. J. Pedersen (E. I. du Pont) in 1967, much effort has been devoted to the synthesis of crown compounds and the related analogues with an eye on their properties of selective complexation towards specific substances. D. J. Cram (University of California at Los Angeles), J. M. Lehn (University Louis Pasteur), and others have developed novel macrocyclic host compounds with attention to molecular detail, and have clarified the relationship between structure and complexation properties. These findings have been systematized as the concept of host-guest chemistry or supramolecular chemistry. The award of the Nobel Prize in chemistry to Pedersen, Cram, and Lehn, in 1987, was the highlight in the field of microcyclic chemistry. On the other hand, at the XIIth ISMC, held in Hiroshima, Japan; and chaired by: Professor Eiichi Kimura of Hiroshima University in 1987, the 20th anniversary of the discovery of crown ether was timely celebrated by awarding the Nobel Prize to the three persons mentioned above. This is regarded as evidence of the level of research in this field, in Japan.

A number of investigators in the United States of America other than Pedersen and Cram, have supported the remarkable development of

macrocyclic chemistry through this series of international symposia on macrocyclic chemistry. R. M. Izatt and J. J. Christensen, Brigham Young University, were the coorganizers of the first symposium on Macrocyclic Chemistry in 1977. The B.Y.U. group, including J. S. Bradshaw and J. D. Lamb, measured and complied equilibrium constants for cationmacrocycle interaction. They also synthesized many new macrocycles and developed membrane separation techniques for a variety of cations. C. L. Liotta, Georgia Institute of Technology, used crown ethers as the phase transfer catalyst for a variety of organic reactions in the early years. G. W. Gokel, University of Miami, created the concept of lariat ethers, which were crown ether derivatives with secondary donating sidearms. R. D. Bartsch, Texas Institute of Technology, developed effective extractant and carriers based on proton-ionizable crown ethers for alkali metal and alkaline earth metal cations. G. R. Newkome, University of South Florida, prepared new crown ethers that contained aromatic subcyclic units. R. Breslow, Columbia University is most famous in cyclodextrin chemistry. Recently, A. D. Hamilton, University of Pittsburgh prepared new macrocycles as synthetic receptors for nucleotide. C. D. Gutche, Washington University, received a great deal of attention in his calixarene chemistry research.

On the other hand, many Japanese chemists have also contributed to this chemistry. E Kimura, Hiroshima University, is the international member of this international symposium. He did an outstanding job in the field of azamacrocycles and was awarded the second Izatt-Christensen Award this year. Y. Murakami, Kyushu University, prepared a watersoluble cyclophane as a vitamin B-dependent holoenzyme model. I. Tabushi, Kyoto University, was one of the leaders in Japan in the field of biomimetic chemistry. K. Koga, Tokyo University, and K. Odashima, Hokkaido University, synthesized novel water-soluble cyclophanes and their inclusion phenomena for a variety of guest compounds. Koga and S. Sasaki, Kyushu University, used choral crown ethers as enzyme model for the synthesis of peptide. M. Takagi, Kyushu University, made chromoionophores based on crown ethers for alkali metal and alkaline earth metal cations. S. Misumi and T. Kaneda, Osaka University, succeeded in recognizing amines by coloration with azophenol-dyed crowns. T. Shono and K. Kimura, Osaka University, applied crown compounds to analytical and separation chemistry. M. Okahara, Osaka University, devel

oped convenient synthetic procedures for simple crown ethers and reactive crown ethers. S. Shinkai, Kyushu University, prepared a variety of functionalist macrocycles such as switched crown compounds and water-soluble calixarenes. H. Ogoshi, Kyoto University, and Y. Aoyama, Nagaoka University of Technology, recently developed new macrocycles discriminating carbohydrates. H. Tsukube, Okayama University, clarified the transport abilities of multiarmed macrocycles across artificial liquid membranes. T. Hakushi, and Y. Inoue, Himeji Institute of Technology, found that the crown ethers with low symmetry often showed excellent selectivity toward a specific ion. Besides them, many researchers are interested in this chemistry.

Synthetic macrocyclic compounds now include crown ethers, cryptands, spherands, carcerands, cavitands, cyclophanes, and calixarenes and are expected to increase the kinds of macrocycles.

TOPICS PRESENTED AT THIS SYMPOSIUM BY THE UNITED STATES OF AMERICA AND JAPAN

E. Kimura from Hiroshima University is the recipient of the 1992 Izatt-Christensen Award. His recent work had involved the design of cation and anion receptor molecules, metalloenzyme models, molecular catalysts, transport agents and photo catalysis of carbon dioxide reduction. At his award presentation, he reported on the roles of zinc(II) in zinc enzymes on the basis of his model study using macrocyclic polyamine.

D. H. Busch from the University of Kansas, gave a plenary lecture on the attempts to perform O2 oxidations within the cavity of a bicyclic cyclidene complex.

T. W. Bell from State University of New York at Stony Brook, presented a plenary lecture on the synthesis of new torands, which are preorganized host compounds that have macrocytic perimeters comprised of fully fused rings, and new uses for old torands. J. L. Sessler from the University of Texas at Austin, showed a new direction in porphyrinrelated research concerning anion binding in his plenary lecture. Some of the expanded porphyrins have an ability to bind anions in their potential protonated form. Y. Murakami from Kyushu University, presented an invited lecture on molecular recognition by novel cage-type azacyclophanes containing choral binding sites in aqueous media.

The usefulness of mass spectroscopy in gasphase studies of host-guest interaction was presented

by J. S. Brodbelt from the University of Texas at Austin. Similarly, D. V. Dearden from the University of Texas at Arlington, reported on the mechanism for the formation of a metal cation macrocycle complex in the gas phase.

R. A. Bartsch from Texas University, presented an invited talk on ionic recognition by proton-ionizable lariat ethers and their polymers. In collaboration with him, T. Hayashita from Saga University, reported on the synthesis and properties of dibenzocrown ether resins having various sidearm groups. C. M. Wai from the University of Idaho, reported on the application of lariat crown ethers containing carboxylic acid and hydroxamic acid moieties to selective extraction of Ianthanides. R. D. Rogers from Northern Illinois University, reported on the crown ether extraction of group 1 and 2 cations in polyethylene glycol-based aqueous biphasic systems at high alkalinity.

L. Echegoyen from the University of Miami, presented and invited lecture on the electron transfer products between metals and C60 K. E. Krakowiak from Brigham Young University, reported on a facile synthetic procedure for preparing cryptands. N. K. Dalley from Brigham Young University, presented an overview on solid state structures of host and host-guest compounds. S. H. Gellman from the University of Wisconsin, reported on the structure and complexation properties of macrocycles containing atoms from the second row of the periodic table such as sulfur and phosphorous. G. W. Gokel from the University of Miami, reported on bimetallic complexation by crown ethers, lariat ethers, and cryptands. E. F. Maverick of D. J. Cram's group from the University of California at Los Angeles, introduced recent advances in carcerand chemistry. E. V. Anslyn from the University of Texas at Austin, reported on polyazaclefts for complexing reactive intermediates. A. E. Kaifer from the University of Miami, reported on the synthesis and properties of asymmetric rotaxanes based on a-cyclodextrin.

C. D. Gutsche from Texas Christian University, gave a critical review on calixarene chemistry. The number of publications concerning the title compounds was demonstrated to sharply increase in a few years. Several related lectures were presented at this symposium.

The author from Osaka University presented an invited talk on the transport of metal ions in the opposite directions across an artificial membrane.

The exchange between Na* and K+ or between Ca2+ and K+ was realized by pH control.

K. Kumar from Bristol-Myers Squibb Pharmaceutical Research Institute, reported on macrocyclic polyaminocarboxylate complexes of lanthanides as magnetic resonance imaging contrast agents. O. A. Gansow from the National Institute of Health, reported on the systematic radiation therapy of cancer by using radioactive metal macrocycles and chelate linked to antibodies. R. W. Taylor from the University of Minnesota, reported on complexation chemistry of ionophores A23187 and Ionomycin. B. E. Jepson from EG & G Mound Applied Technologies, reported on chromatographic enrichment of calcium isotopes with 18-crown-6 bound to a macroporous solid support.

IMPRESSIONS AT THE SYMPOSIUM

Upon my attendance at this symposium, I felt that the chemistry of macrocyclic compounds is more and more expanding its realm. In addition to crown ethers and cryptands, some other macrocyclic compounds such as expanded porphyrins and calixarenes have been demonstrated to be very efficient as the hosts for a variety of guest compounds. This series of symposia really provided an excellent place where each scientist of a variety of researches challenges the clarification of host-guest interactions and can present his/her own results. Although a major part of the contributions to this field of macrocyclic chemistry was really done by Americans, I would like to emphasize that some important contributions were from Japan, as shown in this report.

Dr. Yohji Nakatsuji received his B.S. (1974), M.S. (1976), and Ph.D. (1979) in Applied Chemistry at Osaka University, Japan. Since 1979, he has been a faculty member at Osaka University and is now an associate professor in the Department of Applied Chemistry. During 1984 and 1985, he worked with Professor Jerald S. Bradshaw at Brigham Young University as a postdoctoral fellow. He was awarded the Japan Oil Chemists' Award for Young Scholars in 1990. His research interests include the synthesis and cation complexation properties of macrocyclic compounds and the related open-chain analogues. He is a member of the American Chemical Society and the American Oil Chemists' Society.