Preparation of gamma-siloxyallyltributylstannanes and their use in the synthesis of (+/-)-1-deoxy-6,8a-di-epi-castanospermine

gamma-siloxyallyltributylstannanes were selectively obtained as E or Z isomers from beta-tributylstannylacrolein upon reaction with lithium or magnesium alkylcyanocuprates. The ability of the reagents to give a high syn selectivity when added to iminium salts has been used for the efficient synthesis of (+/-)-1-deoxy-6,8a-di-epi-castanospermine from succinimide. The key step of the synthesis was the allylstannation of the N-allyliminium intermediate followed by ring closing metathesis.     

Monitoring protein interactions in the living cell through the fluorescence decays of the cyan fluorescent protein.

Using fluorescence lifetime microspectroscopy and imaging techniques, we have studied the fluorescence of cyan fluorescent protein (CFP) transiently expressed in HEK-293 cells, in the presence or absence of its fluorescence resonance energy transfer (FRET) partner, yellow fluorescent protein (YFP). When the two proteins are attached through a 27-amino-acid linker, a 33 % average efficiency of intramolecular energy transfer is accurately determined inside the cell. Additionally, we observe a systematic quenching of the CFP fluorescence with increasing levels of protein expression. This quenching cannot be accounted for by formation of the previously described dimer of GFP-related proteins, since its magnitude is unchanged when the fluorescent proteins carry the mutation A206K shown to dissociate this dimer in vitro. Even when the intracellular protein concentration largely exceeds the in vitro dissociation constant of the dimer, self-association remains undetectable, either between free proteins or intramolecularly within the CFP-YFP construct. Instead, the detailed concentration effects are satisfactorily accounted for by a model of intermolecular, concentration-dependent energy transfer, arising from molecular proximity and crowding. In the case of CFP alone, we suggest that self-quenching could result from a pseudo-homo FRET mechanism between different, spectrally shifted emissive forms of the protein. These phenomena require careful consideration in intracellular FRET studies.     

具有偿付约束的衍生证券市场均衡存在性

本文通过一个简单的模型,证明了具有偿付约束的衍生证券市场均衡的存在性,由此解释了衍生证券市场的起因和衍生证券交易所的建立过程.这一结论很好地解释了市场摩擦对均衡存在性的影响,与无摩擦时均衡未必存在在形成了鲜明的对照.     

Oxygenation of thiolates to S-bonded sulfinate in an iron III complex related to nitrile hydratase

Air oxidation of the iron(III) complex derived from (2-mercaptoisobutyryl)-4,5-dichloro-O-phenylenediamine in the presence of Et4NCN afforded the corresponding disulfinato species. With two carboxamido nitrogens trans to two S-bonded sulfinates, this complex mimics the disulfinate inactive form of Fe-NHase.     

A potentially divergent and rapid route to analogues of deoxycyclitols, pentopyranoses, 6-deoxyhexoses, and hexoses

Direct precursors to analogues of pentopyranoses, 6-deoxyhexoses, and hexoses, in which a CF(2) center replaces the pyranose oxygen, have been synthesized rapidly from trifluoroethanol. A simple scaleable allylation reaction delivers ethers which undergo dehydrofluorination/metalation, followed by addition to either acrolein or cinnamaldehyde, to afford allylic alcohols. Fluorine-assisted [3,3]-rearrangement followed by reduction with sodium borohydride delivers diols, which undergo RCM smoothly to afford cyclohexene diols.