A biomimetic domino reaction for the concise synthesis of capreomycidine and epicapreomycidine

The non-proteinogenic amino acids capreomycidine and epicapreomycidine are constituents of antibiotically active natural products, but the synthesis of these unusual cyclic guanidine derivatives is challenging. The biosynthesis of capreomycidine has therefore been employed as a guideline to develop a concise biomimetic synthesis of both epimeric amino acids. The resulting domino-guanidinylation-aza-Michael-addition reaction provides the most convenient access to these amino acids in racemic form. Attempts to dissect the domino reaction into two separate transformations for a stereocontrolled version of this synthetic approach have also been made. The synthesized didehydro-arginine derivatives with urethane-protected guanidine moieties did not undergo the aza-Michael-addition anymore. These results may have wider implications for the 1,4-addition of guanidines to α,β-unsaturated carbonyl compounds, particularly to didehydro amino acids.     

A concise route to triazolobenzodiazepine derivatives via a one-pot alkyne-azide cycloaddition reaction

A new and efficient one-pot synthesis of [1,2,3]triazolo[1,5-a][1,4] benzodiazepin-6(4H)-ones is described starting from readily available anthranilic acids. A small array of the title compounds were assembled via a four-step sequence involving diazotisation, azide addition followed by amide bond formation employing polymer supported carbodiimide and subsequent 1,3-dipolar cycloaddition reaction.     

A concise synthesis of benzimidazoles via the microwave-assisted one-pot batch reaction of amino acids up to a 10-g scale

An efficient method for the synthesis of aminomethyl benzimidazoles is developed by using a one-pot batch reaction between amino acids and o-phenylenediamines. This reaction proceeds smoothly in an unmodified household microwave oven, even though scale-up is to 10 g. A desirable method for the quick synthesis of benzimidazoles, which are used as a kind of important intermediates in drug synthesis, is provided by the scale-up utilization of amino acid resource.     

A concise synthesis of photoactivatable 4-aroyl-L-phenylalanines

An efficient preparation of the title compounds from 4-iodo-L-phenylalanines using a carbonylative Stille cross-coupling reaction as the key-step is described.     

A concise synthesis of β-sitosterol and other phytosterols

A convenient synthesis of sidechain-modified phytosterols is achieved via a temporary masking of the stigmasterol 5,6-alkene as an epoxide. Following performance of the desired modification, the alkene is regenerated through a mild deoxygenation. The approach is applied to the syntheses of β-sitosterol and campesterol acetate, and suggests a facile route to the (Z)-isomers of Δ^22-23 phytosterols.     

Sure facts, speculations, and open questions about the evolution of transposable element copy number

Transposable elements (TEs) are sequences capable of multiplying in their host's genome. They survive by increasing copy numbers due to transpositions, and natural selection washes them out because hosts with heavier loads of TEs have lower fitness. The available phylogenetic evidence supports the view that TEs have existed in living organisms for hundreds of millions of years. A fundamental question facing the field is how can an equilibrium be attained between transposition and selection which allows these parasitic genetic elements to persist for such a long time period? To answer this question, it is necessary to understand how the rate of TE transposition is controlled and to describe the mechanisms with which natural selection opposes TE accumulation. Perhaps the best models for such a study are copia and gypsy retrotransposons in Drosophila. Their average rate of transposition in nature is between 10^?5 ? 10^?4 transpositions per copy per generation. Unlike nature, transposition rates vary widely, from zero to 10^?2, between laboratory lines. This variability in transposition rate is controlled by host genes. It is probable that in nature TE site heterogeneity is caused by frequent transpositions in rare flies with permissive alleles, and no transpositions happen in the rest of flies. The average rate of TE transposition in nature may thus depend on the frequency of permissive alleles, which is a function of the rate of mutation from restrictive to permissive alleles, the mechanism and the strength of selection opposing TE multiplication, and population size. Thus, evolution of the frequency of permissive alleles of genes controlling transposition must be accounted for to understand evolution of TE copy numbers.     

农村留守孩心理健康的家庭因素研究

青少年时期是儿童个性发展的一个重要时期,个性发展有较大的可塑性。目前农村劳动力迁移导致了大批留守儿童亲子教育缺失和家庭教育缺位。本文对留守儿童心理健康的相关研究进行了整理,分析了影响留守儿童心理健康状况的四个主要家庭因素,并总结了关于为留守儿童建立社区学校和家庭的三维支持系统的建议。     

A concise necessary and sufficient condition for the existence of a galled-tree

Galled-trees are a special class of graphical representation of evolutionary history that has proven amenable to efficient, polynomial-time algorithms. The goal of this paper is to construct a concise necessary and sufficient condition for the existence of a galled-tree for M, a set of binary sequences that purportedly have evolved in the presence of recombination. Both root-known and root-unknown cases are considered here.     

Interferons and oncogenes in the control of cell growth and differentiation: working hypothesis and experimental facts

This short review summarizes available evidence for (i) growth regulatory properties of exogenous as well as recently described autocrine IFNs, (ii) down-regulation of cellular oncogene expression with emphasis on c-myc and (iii) the possible involvement of the IFN-regulated 2-5A pathway at these levels. Initially described as a part of the IFN-induced antiviral mechanism, this double-stranded RNA-activated pathway leads to the preferential degradation of viral mRNAs in IFN-treated virus-infected cells probably through localized activation at the site of virus replication. Such mechanisms could be involved in the regulation of the stability of rapidly turning over mRNAs as for instance c-myc mRNA in IFN-treated cells. Whatever the elegance of the concept, however, experimental evidence is essentially circumstantial; tools developed in our group to strengthen the demonstration are briefly described.     

A concise review of common animal models for the study of limb regeneration

Correct selection of an appropriate animal mode to closely mimic human extremity diseases or to exhibit desirable phenotypes of limb regeneration is the first critical step for all scientists in biomedical and regenerative researches. The commonly-used animals in limb regeneration and repairing studies, such as axolotl, mice, and rats, are discussed in the review and other models including cockroaches, dogs, and horses are also mentioned. The review weighs the general advantages, disadvantages, and precedent uses of each model in the context of limb and peripheral injury and subsequent regeneration. We hope that this review can provide the reader an overview of each model, from which to select one for their specific purpose.     

Dynamics of the summary electrical activity of the dorsal hippocampus during development of experimental informational behavioral pathology

Dynamics of dorsal hippocampal EEG changes were traced in cats during the short-term memory loads under conditions of the time deficit between the separate delayed reactions. Shortening the intervals between the tests from 3-5 min to 15-20 s led to an expressed ECoG desynchronization accompanied by an initial increase and later blockade of the hippocampal theta-rhythm. Hippocampal theta-activity changes under conditions of the time deficit was a result of emotional stress. The long emotional stress impaired the short-term image memory, and this was manifested in hippocampal theta-rhythm disappearance.     

A summary of geographical characteristics of the Galapagos Islands

Republished here, with permission, in a slightly modified form, from Noticias de Galapagos 55, July 1995, 18–24. Copyright remains, by agreement, with Noticias de Galápagos , which is published by The Charles Darwin Foundation for the Galápagos Islands.     

A concise synthesis of the 3-O-beta-D- and 4'-O-beta-D-glucuronide conjugates of trans-resveratrol

trans-Resveratrol ((E)-3,4',5-trihydroxystilbene, 1) is a phytoalexin produced naturally in plants and grape skins as a stress metabolite protecting against fungal attack. Widespread interest in this apparently structurally simple molecule and synthetic stilbene analogues has arisen in recent years due to the discovery of its antioxidant, antiinflammatory, and anti-carcinogenic activities, among others. Although O-conjugation with glucuronic acid in vivo is known to represent a significant metabolic pathway for polyphenolic compounds in general and 1 in particular, preclinical studies have been hampered by the lack of chemically pure, completely characterized reference standards of both regioisomeric 3-O-beta-d- and 4'-O-beta-d-glucuronide conjugates of 1 for adequate identification and quantification of these significant metabolites. The present work describes a concise, convergent synthesis of both 3-O-beta-d- and 4'-O-beta-d-glucuronide conjugates of 1 using a strategy based on a novel Heck coupling of iodoaryl-O-beta-d-glucuronate esters with appropriately substituted styrenes, such that highly pure multimilligram to gram quantities of both the 3-O-beta-d- and 4'-O-beta-d-glucuronide conjugates of 1 can now be conveniently synthesized.