摘要:

AbstractLife on earth is based on compounds that have carbon frames and backbones. Today, chemists have added to the world of biomolecules and biopolymers approximately 107different synthetic molecules and polymers, the structures of which also depend on the formation of strong, stable carbon–carbon bonds. Although the stability of carbon–carbon bonds has been recognized for more than a century, the two natural modifications graphite and diamond were, until recently, the only allotropic forms of carbon on earth that were available in macroscopic quantities and were structurally well characterized. With the synthesis of macroscopic quantities of buckminsterfullerene (C60) and the higher fullerenes (C70, C76, C78, etc.) and the exploration of the fascinating properties of these all‐carbon spheres, this situation has completely changed. In the coming decades, the design, preparation, and study of novel molecular and polymeric allotropic forms of carbon will be a central topic in chemistry. Research in this area will dramatically advance the fundamental knowledge on carbon‐based matter and, as already illustrated by the ongoing work on C60, generate unprecedented technological perspectives. This review surveys synthetic organic‐chemical approaches toward the preparation and study of all‐carbon molecules and polymers that differ from the familiar networks of graphite and diamond as well as from the fullerenes. We will also discuss the ongoing research on fullerenes with a particular focus on the synthetic approaches to these all‐carbon spheres and their transition me

ISSN:0570-0833    

DOI:10.1002/anie.199211013

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractChemists have for a long time considered molecules simply in terms of their constitution. The importance of molecular shape was recognized perhaps for the first time by the semio‐chemists, who were interested in the interactions of fragrant substances with a receptor. Apart from the case of rigid molecules, our ideas and concepts of molecular shape simply reflect an instantaneous situation, because flexible molecules take advantage of the whole range of conformation that is available to them. Nature frequently utilizes flexible molecules whose conformational space is restricted, in other words, molecules that can adopt only a few preferred conformations. This review discusses some of the principles that nature employs in order to impart a defined shape to flexible molecules. The purposeful application of these principles then allows the conformational design of molecular skeletons.For corrigendum see DOI:10.1002/anie.199215401For corrigendum see DOI:10.1002/anie.1992165

ISSN:0570-0833    

DOI:10.1002/anie.199211241

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractA Cook's tour is presented of the organosulfur chemistry of the genusAllium, as represented, inter alia, by garlic (Allium sativumL.) and onion (Allium cepaL.). We report on the biosynthesis of theS‐alk(en)yl‐L‐cysteineS‐oxides (aroma and flavor precursors) in intact plants and on how upon cutting or crushing the plants these precursors are cleaved by allinase enzymes, giving sulfenic acids—highly reactive organosulfur intermediates. In garlic, 2‐propenesulfenic acid gives allicin, a thiosulfinate with antibiotic properties, while in onion 1‐propenesulfenic acid rearranges to the sulfine (Z)‐propanethialS‐oxide, the lachrymatory factor (LF) of onion. Highlights of onion chemistry include the assignment of stereochemistry to the LF and determination of the mechanism of its dimerization; the isolation, characterization, and synthesis of thiosulfinates which most closely duplicate the taste and aroma of the freshly cut bulb, and additional unusual compounds such as zwiebelanes (dithiabicyclo[2.1.1]hexanes), a bis‐sulfine (a 1,4‐butanedithialS,S′‐dioxide), antithrombotic and antiasthmatic cepaenes (α‐sulfinyl disulfides), andvic‐disulfoxides. Especially noteworthy in the chemistry of garlic are the discovery of ajoene, a potent antithrombotic agent from garlic, and the elucidation of the unique sequence of reactions that occur when diallyl disulfide, which is present in steam‐distilled garlic oil, is heated. Reaction mechanisms under discussion include [3, 3]‐ and [2, 3]‐sigma‐tropic rearrangements involving sulfur (e.g. sulfoxide‐accelerated thio‐ and dithio‐Claisen rearrangements) and cycloadditions involving thiocarbonyl systems. In view of the culinary importance of alliaceous plants as well as the unique history of their use in folk medicine, this survey concludes with a discussion of the physiological activity of the components of these plants: cancer prevention, antimicrobial activity, insect and animal attractive/repulsive activity, olfactory–gustatory–lachrymatory properties, effect on lipid metabolism, platelet aggregation inhibitory activity and properties associated with ajoene. And naturally, comments about onion and garlic induce

ISSN:0570-0833    

DOI:10.1002/anie.199211351

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.199211791

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.199211811

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.199211831

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.199211851

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.199211891

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.199211901

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.199211921

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY