Substitution with retention in organoboranes and utilization of the phenomenon for a general synthesis of pure enantiomers

Organoboranes, readily available via the hydroboration of unsaturated organic compounds, exhibit a remarkable versatility in their reactions. The boron atom in these organoboranes can be readily converted into a wide variety of organic groups under very mild conditions, providing simple versatile syntheses of organic compounds. Exploration of these substitution reactions reveal that, with rare exceptions, the organoboranes transfer the alkyl group to other elements of synthetic interest with complete retention of stereochemistry. Recently we have discovered a method of synthesizing essentially optically pure organoborane intermediates. These optically active alkyl groups attached to boron can also be transferred with complete retention of optical activity. Consequently, it is now possible to achieve by a rational synthesis the preparation of almost any optically active compound with a chiral center, either R- or S-, in essentially 100% enantiomeric excess.     

An efficient and general method for resolving cyclopropene carboxylic acids

A general method is described for the resolution of cycloprop-2-ene carboxylic acids via diastereomeric N-acyloxazolidines prepared from enantiomerically pure oxazolidinones. Although a number of oxazolidinones were shown to resolve cyclopropene carboxylic acids, the oxazolidinones of S-phenylalaninol, S-phenylglycine and (1S,2R)-cis-1-amino-2-indanol are optimal in terms of resolving power and cost effectiveness. Separations were performed using simple flash chromatography, and because there is typically a large difference in R_f values it is possible to separate gram quantities of pure diastereomers in a single chromatogram. The cycloprop-2-ene carboxylic acids that can be resolved include those that are substituted at the 1-position by H, Ph, α-naphthyl, CO₂Me, CH₂OMOM, and trans-styryl; alkene substituents include Me, n-alkyl, Ph and tethered alkynes. Remarkably, 2-methyl-3-propylcycloprop-2-ene carboxylic acid can also be resolved with ease. The relative configurations of four diastereomerically pure oxazolidines were determined by X-ray crystallography. Reduction of the N-acyloxazolidinones with LiBH₄ give enantiomerically pure derivatives of 3-hydroxymethylcyclopropene that react with either MeMgCl or vinylMgCl and catalytic CuI to give enantiomerically pure products of syn-addition.     

Optimal life strategies in organisms exposed to recurrent critical events

The optimal partition of energy between survival and reproduction is considered for a population subject to recurrent and potentially lethal critical events. The best strategy is found by maximizing fitness, a functional derived from the Lotka equation. The dynamics is governed by a second-order, age-varying, nonlinear system. The energy storage and the probability of survival are the state variables, while the amounts of energy placed into and withdrawn from the storage are the controls. The optimal life strategy is shown to be as follows: build up the storage at the very beginning of life, and then progressively deplete it to resist the critical events.This work was partially supported by MURST Project Ricerche sui Fondamenti della Conservazione della Natura. The authors would like to thank C. Ricci for suggesting the problem and C. Matessi for helpful discussion.     

单一稀土Ce, La和混合稀土在工业纯铝中的作用

通过对比实验的方法，研究了稀土Ce，La和混合稀土对工业纯铝组织、电性能和机械性能的影响。结果表明：单一稀土La，Ce可降低工业纯铝的电阻率，提高工业纯铝的导电性，其中La的效果优于Ce．而混合稀土对电阻率几乎无影响；La，Ce和混合稀土均能减小工业纯铝的晶粒度，在其加入量为0．1％后细化效果明显，当其含量大于0．5％后细化效果趋于平缓，其中Ce的效果最佳，La次之，混合稀土最弱；单一稀土La，Ce在一定含量时可提高工业纯铝的σb6和δ，Ce的作用强于La，混合稀土对σb和δ的影响不明显。     

A concise synthesis of (2S,4R)- and (2S,4S)-4-methylglutamic acid

A concise, multi-gram scale method for producing the bioactive and enantiomerically pure epimers, (2S,4R)- and (2S,4S)-glutamic acids, in a single synthetic scheme is described.     

Pheromone, 3.Mitt.: Eine einfache Methode zur Steuerung der Reduktion von α-Alkoxy-carbonylverbindungen

Summary Enantiomerically pure 1,2-diols bearing optionallysyn oranti configurated secondary hydroxylic groups are synthesized from acetal-protected cyanohydrins. After resolution of the diastereomers the cyanohydrins are converted into -alkoxy-ketones by Grignard-reaction followed by reduction using common chelating or non-chelating agents. Among others syntheses of enantiomerically pure pheromones,endo-Brevicomin,exo-Brevicomin and Dispalure are given as examples.

Prof. Dr. Hans Berbalk zum 70. Geburtstag gewidmet     

Average kinetic energy of ions ejected from pure Coulomb explosions of methane clusters

We use an electrostatic model to study the average kinetic energy of ions ejected from the pure Coulomb explosions of methane clusters (CA4)n (light atom A=H and D). It is found that the ratio of the average kinetic energy of the ions to their initial average electrostatic potential energy is irrelevant to the cluster size. This finding implies that as long as the ratio is given, the average kinetic energies of the ions can be simply estimated from their initial average electrostatic potential energies, rather than from the time- consuming simulations. The ratios for the different charge states of carbon ions are presented.     

Asymmetric Synthesis, Antifungal Activity and Molecular Modeling of Iodiconazole Isomers

Iodiconazole is a novel antifungal agent that was developed in its racemic form. In order to investigate the ef- fects of the chiral center on the antifungal activity, R- and S-isomers of iodiconazole were prepared on the basis of the asymmetric Sharpless epoxidation. （S）-Iodiconazole was proved to have better antifungal activity than the （R）- isomer. The binding modes of the two isomers with lanosterol 14~z-demethylase were clarified by molecular dock- ing.