This article describes the synthetic studies on various types of natural products and its relative compounds which include reserpine, yohimbine, dehydrocorynantheol, antirhine, prostaglandin analogues, secologanin, semburine and 11-ketosteroid, using the common synthon easily derived from symmetrical compounds such as maleic anhydride and D-mannitol as illustrated in Fig.1 and 2.
Convergent and enantiospecific total syntheses of rifamycin W ansa-chain compound (48) and erythronolide A (61) were achieved by the use of a “two-stage coupling” process, which was developed for stereocontrolling the carbon chain connections in the synthesis. The new coupling process consists of the first stage of addition reaction of appropriate vinyllithio compounds to 2-methyl-substituted aldehydes and the second stage of homogeneous hydrogenation with Wilkinson's catalyst of the major “Cram” type of addition products. In the practical total syntheses of 48 and 61, the process gave predominantly “Cram” (syn) -anti type of coupling products to provide the proper chiral sequences of 48 and (9 S) -9-dihydroerythronolide A which was an important pre-cursor of 61. Principal stereochemical features of this process are described for using it effectively in natural product synthesis.
Since the discovery of two endogenous opioid peptides, Met-and Leu-enkephalins, a lot of works have been done to develop better analgesics without side-reactions. By now many highly potent analogues of enkephalins have been designed and synthesized. But, pure analgesics have not so far been obtained. It is mainly because of the complexity of opioid ligands and their interactions with multiple receptors. In addition recent knowledge of enhancing effects of peptidase inhibitors on the potency of opioid peptides prompts us to reexamine all the accumulated pharmacological data.
Synthesis of phosphorothioates and their properties are reviewed from the standpoint of organophosphorus chemistry. Inherent synthetic problems in the P-S bond formation are described. Several methods for the synthesis of nucleoside phosphorothioates are introduced and their application to oligonucleotide synthesis is also described from various aspects. Especially, the versatile utility of the bis (phenylthio) phosphoryl group, which can be readily introduced to nucleoside hydroxyls, is shown with several successful examples of the synthesis of DNA and RNA fragments.
This review summarized the strategy and use of allylic and pentadienyl dithiocarbamates in organic synthesis, and focuses on a new [3, 3] -sigmatropic rearrangement of the α-alkylated allylic dithiocarbamates to the γ-alkylated ones with 100 % trans-selectivity, which are followed by the realkylation, allylation, or functional group interconversion at the newly created a-methylene group. Thus, these reagents have a highly potential utility in the stereoselctive syntheses of monoenes, dienes, trienes, and tetraenes, and are also used for the preparation of allylic halides and alcohols, α, β-unsaturated aldehydes, vinyl thiiranes, acyclic terpenes, and a variety of silyl reagents.