An improved large scale synthesis of 1,4-anhydro-4-thio-d-ribitol

An improved large scale synthesis of 1,4-anhydro-4-thio-d-ribitol (4) from d-ribose has been accomplished by combining the O-allyl and O-p-methoxybenzyl protecting groups. Compound 4 was obtained in 31% yield in eight steps with three chromatographic separations.     

Mild benzhydrylation and tritylation of saccharidic hydroxyls promoted by acid washed molecular sieves

Commercially available 4 Å acid washed molecular sieves (AW 300 MS) promote the protection of primary and secondary saccharidic alcohols through a dehydration mechanism and in the absence of any strong protic or Lewis acid.     

烯丙基保护基在多羟基化合物中的应用

烯丙基保护基由于能够在温和的反应条件下,在羟基、氨基等基团中引入和脱除,并且具有很好的区域选择性和化学选择性,因此被广泛应用于有机合成中。本文介绍了烯丙基保护基的发展历史,综述了烯丙保护基对多羟基化合物中不同羟基的选择性保护应用,并阐述了烯丙保护基的引入和脱除的机理及方法。     

A practical method for building linear and cyclic triamines from (2-trimethylsilyl)ethanesulfonamides (SES-amides)

SES-chloride has been obtained in higher yield and purity by improving Weinreb's original procedure, allowing efficient access to the primary SES-amide. Linear triamines can be built conveniently from the SES-amide in high yields, with the potential for orthogonal protection. The modified Richman-Atkins cyclisation of SES-amides allows access to novel biologically interesting triazamacrocycles with combinations of three-, four-, five- and six-carbon bridges within the ring. Purification of the free macrocyclic amines by distillation greatly simplifies the workup, increasing the practicability of multi-gram scale synthesis. Although CsF sometimes provided undesirably low yields in the deprotection step, alternative fluoride sources were found to be unsuitable for the deprotection of SES-triazamacrocycles.     

N-Amino-1,8-Naphthalimide is a Regenerated Protecting Group for Selective Synthesis of Mono-N-Substituted Hydrazines and Hydrazides

A new route to synthesis of various mono-N-substituted hydrazines and hydrazides by involving in a new C−N bond formation by using N-amino-1,8-naphthalimide as a regenerated precursor was invented. Aniline and phenylhydrazines are reproduced upon reacting these individually with 1,8-naphthalic anhydride followed by hydrazinolysis. The practicality and simplicity of this C−N dihalo alkanes; developed a synthon for bond formation protocol was exemplified to various hydrazines and hydrazides. N-amino-1,8-naphthalimide is suitable synthon for transformation for selective formation of mono-substituted hydrazine and hydrazide derivatives. Those are selective mono - amidation of hydrazine with acid halides; mono-N-substituted hydrazones from aldehydes; synthesis of N-aminoazacycloalkanes from acetohydrazide scaffold and inserted to hydroxy derivatives; distinct synthesis of N,N-dibenzylhydrazines and N-benzylhydrazines from benzyl halides; synthesis of N-amino-amino acids from α-halo esters. Ecofriendly reagent N-amino-1,8-naphthalimide was regenerated with good yields by the hydrazinolysis in all procedures.     

Next‐Generation o‐Nitrobenzyl Photolabile Groups for Light‐Directed Chemistry and Microarray Synthesis

Light as an external trigger is a valuable and easily controllable tool for directing chemical reactions with high spatial and temporal accuracy. Two o‐nitrobenzyl derivatives, benzoyl‐ and thiophenyl‐NPPOC, undergo photo‐deprotection with significantly improved efficiency over that of the commonly used NPPOC group. The two‐ and twelvefold increase in photo‐deprotection efficiency was proven using photolithograph synthesis of microarrays.     

An easy and versatile approach for the regioselective de-O-benzylation of protected sugars based on the I2/Et3 SiH combined system

The use of cheap and easy to handle reagents, such as I(2) and Et(3) SiH, at low temperature allows the regioselective removal of benzyl protecting groups from highly O-benzylated carbohydrates. The observed regioselectivity is dependent on the nature of the precursor, the least accessible carbinol often being liberated. A mechanistic investigation reveals that in situ generated HI is the promoter of the process, whereas the regioselectivity appears to be mainly controlled by steric effects. However, the presence of an electron withdrawing acyl protecting group can switch the regioselectivity to favour deprotection of the carbinol position farthest from the ester group. The protocol is experimentally simple and provides straightforward access in useful yields to a wide range of partially protected mono- and disaccharide building blocks that are valuable for the synthesis of either biologically useful oligosaccharides or highly functionalised chiral compounds. Partially protected sugars thus obtained can also be coupled in situ with a glycosyl donor, as illustrated by the one-pot synthesis of a Lewis X mimic from fully protected precursors.     

聚苯胺盐在无溶剂条件下有效催化羰基保护反应

合成了自掺杂聚苯胺盐PABSA,并成功应用于醛和乙酸酐的缩醛化反应,发现此聚苯胺盐催化剂具有高效、可回收等特性。同时,利用二元醇作为保护基团,醛也可以转化成相应的缩醛。考察了反应时间、温度和催化剂用量对反应的影响,并通过IR、1H NMR、13C NMR和元素分析对部分产物进行了结构表征。     

Studies on Quinones. XIX. Improved Synthesis of 2-Nitro-1,4-benzoquinone and its Reaction with Nucleophiles

Reaction of 2-nitro-1,4-benzoquinone (4), easily obtained by oxidation of 3 with MnO₂/HNO₃, with various nucleophiles affords the corresponding adducts in high yields.     

Going to extremes: "super" armed glycosyl donors in glycosylation chemistry

This concept article gives an overview of stereoelectronic effects in monosaccharide systems and how these can be used to dramatically enhance the reactivity of glycosyl donors in oligosaccharide synthesis.     

Prometabolites of 5‐Diphospho‐myo‐inositol Pentakisphosphate

Diphospho‐myo‐inositol phosphates (PP‐InsP_y) are an important class of cellular messengers. Thus far, no method for the transport of PP‐InsP_y into living cells is available. Owing to their high negative charge density, PP‐InsP_y will not cross the cell membrane. A strategy to circumvent this issue involves the generation of precursors in which the negative charges are masked with biolabile groups. A PP‐InsP_y prometabolite would require twelve to thirteen biolabile groups, which need to be cleaved by cellular enzymes to release the parent molecules. Such densely modified prometabolites of phosphate esters and anhydrides have never been reported to date. This study discloses the synthesis of such agents and an analysis of their metabolism in tissue homogenates by gel electrophoresis. The acetoxybenzyl‐protected system is capable of releasing 5‐PP‐InsP₅ in mammalian cell/tissue homogenates within a few minutes and can be used to release 5‐PP‐InsP₅ inside cells. These molecules will serve as a platform for the development of fundamental tools required to study PP‐InsP_y physiology.     

Current Synthesis of Triterpene Saponins

It′s complicated! Triterpene saponins are a structurally and biologically diverse class of glycoconjugates of triterpenes that are widely distributed in terrestrial plants and some marine organisms. Current synthesis of these complex glycoconjugates has been discussed, whereupon the stereocontrolled glycosylation, global protection/deprotection, and the total synthesis of four unusual triterpene saponins are highlighted.

     

Stereoselective Glycosylation of Glucosamine: The Role of the N‐Protecting Group

Oligosaccharides and glycoconjugates play an important role in biological processes. The use of these complex polymers as biocompatible materials for medicinal applications as well as therapeutic agents for the treatment of several diseases has attracted considerable interest. However, these investigations require large and pure amounts of glycostructures. Glucosamine is one of the major building blocks of these highly important glycoconjugates. Recently, considerable synthetic efforts have been devoted to improving stereoselective glycosylation. In this Focus review, the role of the amine protecting group in the outcome of the glucosamine glycosylation reaction is highlighted.