A short and concise synthesis of isofagomine, homoisofagomine, and 5′-deoxyisofagomine

Applications of the Wittig-Still Rearrangement in Organic Synthesis

This Review traces the discovery of the Wittig-Still rearrangement and its applications in organic synthesis. Its relationship to Wittig rearrangements is discussed along with detailed analysis of E/Z- and diastereoselectivity. Modifications of the products arising from the Wittig-Still rearrangement are reviewed in the context of increased complexity in intermediates potentially useful in target-oriented synthesis. Early applications of the Wittig-Still rearrangement to modifications of steroids are reviewed as are applications to various terpene and alkaloid natural product targets and miscellaneous compounds. To the best of our knowledge, the literature is covered through December 2016.

[Synthetic medicinal chemistry of the biomolecular components mimics]

We are studying the medicinal synthetic chemistry of biomolecular component mimics such as carbohydrates, nucleosides, amino acids, and peptides. In this review, the synthesis and biological activities of iminosugars as carbohydrate mimics are discussed. Glycosidases and glycosyltransferases are involved in a wide range of anabolic and catabolic process, including digestion, the lysosomal catabolism of glycoconjugates, glycoprotein biosynthesis. Hence, modifying or blocking these processes in vivo using inhibitors is a topic of great interest from the therapeutic point of view. Iminosugars are sugars in which the endocyclic oxygen is replaced by a basic nitrogen atom. They are regarded as transition state mimics in certain types of enzyme reactions. This makes the field of iminosugars as carbohydrate mimics an exciting area of research. We synthesized all of the stereoisomers of polyhydroxypiperidines such as fagomine, 1-deoxynojirimycine, and isofagomine. In addition, their both enantiomers, as substrates for a variety of glycosidases were evaluated. Secondly, the asymmetric synthesis of α-1-C-alkyl-arabinoiminofuranoses was achieved by asymmetric allylic alkylation, RCM, and Negishi cross coupling as key reactions. Surprisingly, the L-forms showed a quite potent inhibitory activity toward rat intestinal maltase, while the activities of the D-forms were much weaker. Some of the prepared L-forms showed potent inhibitory activities towards intestinal maltase, with IC₅₀ values comparable to those of commercial drugs such as acarbose, voglibose, and miglitol, which are used in the treatment of type 2 diabetes. Among them, the inhibitory activity towards intestinal sucrase of α-1-C-L-butylarabinoiminofuranose was quite strong towards intestinal sucrase compared to the above commercial drugs.

Acceleration effect of an allylic hydroxy group on ring-closing enyne metathesis of terminal alkynes: scope, application, and mechanistic insights

An interesting acceleration effect of an allylic hydroxy group on ring-closing enyne metathesis has been found. Ring-closing enyne metathesis of terminal alkynes possessing an allylic hydroxy group proceeded smoothly without the ethylene atmosphere generally necessary to promote the reaction. The synthesis of (+)-isofagomine with the aid of this efficient reaction has been demonstrated. Mechanistic studies of the acceleration effect were also carried out. Results of NMR studies suggested that the reaction proceeded via an "ene-then-yne" pathway. Kinetic studies indicated switching of the rate-determining step as a consequence of the presence of an allylic hydroxy group. These results suggest acceleration of the reentry step of Ru-carbene species by the allylic hydroxy group.