Amination of Ethyl 5-Amino-1-Qlycofuranosylimidazole-4-Carboxylates Using Trimethylaluminium

Abstract

Ethyl 5-amino-1-8-D-ribofuranosyl- and arabinofuranosyl imidazole-4-carboxylates were aminated by ammonia, primary and secondary amines to their corresponding 4-carboxamides using trimethylaluminium.     

Synthèse de nucléosides pyrimidiquesàpartir de 1,2-anhydro-4-désoxy-3-O-méthyl-pentopyranoses

Monotosylation of 4-deoxy-3-O-methyl-dl-threo- and -erythro-pentopyranose led, in 62–68% yield, to the 2-O-tosyl derivatives which, on treatment at room temperature with sodium hydride in anhydrous ether, gave quantitatively 1,2-anhydro-4-deoxy-3-O-methyl-dl-threo- and -erythro-pentopyranose, respectively. These epoxides reacted with 2,4-dimethoxypyrimidine in the presence of pyridinium hydrochloride to give, in 68–78% yield, 1-(4-deoxy-3-O-methyl-β-dl-erythro- and -α,β-dl-threo-pentopyranosyl)-4-methoxy-2-pyrimidinone, respectively. Isomers having a trans-1′,2′ configuration were preponderantly formed by an Sn2 reaction.     

Differences in contribution of biological nitrogen fixation to yield performance of common bean cultivars as assessed by the 15N natural abundance technique

Plant and Soil - Identification of variability in biological N2 fixation (BNF) contribution among common bean (Phaseolus vulgaris L.) cultivars under field conditions requires a reliable...     

Social Norms of Cooperation in Small-Scale Societies

Indirect reciprocity, besides providing a convenient framework to address the evolution of moral systems, offers a simple and plausible explanation for the prevalence of cooperation among unrelated individuals. By helping someone, an individual may increase her/his reputation, which may change the pre-disposition of others to help her/him in the future. This, however, depends on what is reckoned as a good or a bad action, i.e., on the adopted social norm responsible for raising or damaging a reputation. In particular, it remains an open question which social norms are able to foster cooperation in small-scale societies, while enduring the wide plethora of stochastic affects inherent to finite populations. Here we address this problem by studying the stochastic dynamics of cooperation under distinct social norms, showing that the leading norms capable of promoting cooperation depend on the community size. However, only a single norm systematically leads to the highest cooperative standards in small communities. That simple norm dictates that only whoever cooperates with good individuals, and defects against bad ones, deserves a good reputation, a pattern that proves robust to errors, mutations and variations in the intensity of selection.