Epoxides are widely recognized as an extremely useful electrophile in view of their enhanced reactivity attributable to a high degree of ring strain, but the reaction of an epoxide as a nucleophile, i.e., oxiranyl anion, is less common. The application of oxiranyl anions in organic synthesis provides a new methodology to introduce an oxiranyl group directly into organic molecules, where new complex carbon skeleton as well as new functionality is created. The generation and reaction of oxiranyl anions as well as the synthetic applications are highlighted in this review.
Chemical modification of the sugar moiety in nucleoside is one of the promising way to find a new chemotherapeutic agent. Nucleoside possessing a heterocyclic or carbocyclic ring instead of 2-deoxyribose or ribose is so called pseudo nucleoside. Since HIV (human immunodeficiency virus) has appeared to cause the serious disease in the human life, such nucleosides have received considerable attentions as a new anti-viral medicine. 4' -Thio-nucleoside in which furanose ring oxygen atom is replaced by a sulfur atom, is of our interest and this review describes the synthesis of 2' -deoxy-4' -thioribonucleo-sides. Specific features in this article include (i) preparation of 2-mercapto-1, 3-diols by acyclic stereocontrol, (ii) synthesis of 2-deoxy-4-thioribose, (iii) glycosidation reaction of thiosugar, and (iv) synthesis and biological activity of 2' -deoxy-4' -thio pyrimidine nucleosides.
A biomimetic oxidizing system “Cu2+-ascorbic acid-O2” was effective for selective conversion of ο-alkoxyphenols into oxido-labile catechols. First direct preparation of 3-hydroxycoumarins from coumarins was achieved by using this system. The oxidizing system hydroxylated phenols to afford catechols and hydroquinones. An unusual substituent effect was observed on this hydroxylation of phenols. Some of the derived catechols and 3-hydroxycoumarins exhibited much greater bio-activities than those of the mother compounds. Mechanistic investigation has revealed that catechols were formed via ipso-substitution of alkoxy groups of ο-alkoxyphenols for hydroxy group.
We found that phospholipase D from Streptomyces sp. (PLDP) effectively catalyzed transphosphatidylation, i.e., the regiospecific transfer of the phosphatidyl residue from phosphatidylcholines to alkanols. The scope of this enzymatic reaction was investigated in detail to develop an efficient method for preparing various phospholipid derivatives. Using this enzymatic method, 5'-Ο-phosphatidyl derivatives of antitumor nucleosides were successfully synthesized to identify potent antitumor drugs. 5'-Ο-Phosphatidyl derivatives of DMDC (2'-deoxy-2'-methylenecytidine) and CNDAC [1- (2-C -cyano-2-deoxy-β-arabino-pentofuranosyl) cytosine], antitumor nucleosides developed by us, showed significant antitumor effects in mice which clearly surpassed those of parent compounds. We have also demonstrated that 5'-Ο-phosphatidylnucleosides can be used as a drug delivery system for lymph : 5'-Ο-phosphatidyl-5-fluorouridine given orally is absorbed via the deacylation-reacylation cycle, a specific pathway for natural phospholipids, to be transported selectively to the lymph.
This article deals with novel organic reactions starting from α-hydroxymonothioacetals. Topics included are (1) preparation of α- (phenylthio) aldehydes from α-hydroxymonothioacetals, (2) stereocontrolled addition of methyltitanium reagents to α- (phenylthio) aldehydes, (3) synthesis of various allylic sulfides, (4) acyclic 1, 4-diastereoselective reduction in (E) -γ-substituted α-enones, (5) divergent synthesis of 1, 3- and 1, 4-diketones, (6) mechanistic insight into allylmetal-thioacetal reactions employing 2-acetoxy-2-phenylacetaldehyde thioacetals, and (7) synthesis of acetylenes and olefins through cross coupling of aldehydes.