Masami Ohtsuka

Bio: Masami Ohtsuka is an academic researcher from Keio University. The author has contributed to research in topics: Total synthesis & Cyclitol. The author has an hindex of 10, co-authored 22 publications receiving 469 citations.

Total synthesis of antibiotic hygromycin A

Abstract: The first total synthesis of the antibiotic (−)-hygromycin A (1) has been achieved by a coupling reaction of the sugar moiety (2) and the cyclitol moiety (3). Both components were synthesized in homochiral forms starting from D-glucose. This synthesis fully confirmed the unique structure of 1, which is much different from other usual aminocyclitol antibiotics

Total Synthesis of (+)-Lycoricidine and Its 2-Epimer from d-Glucose

Abstract: Stereoselective total synthesis of antimitotic alkaloid (+)-lycoricidine (1) and its 2-epimer (30) was accomplished starting from D-glucose. The key steps in this synthesis are (i) a catalytic version of the Ferrier rearrangement for the preparation of the optically active substituted cyclohexenone (the C-ring of lycoricidine) and (ii) a Pd-catalyzed intramolecular Heck-type reaction for construction of the phenanthridone skeleton. A preliminary biological assay revealed that the stereochemistry at the 2-position of lycoricidine plays an important role in its cytotoxic activity

Synthesis of optically active substituted cyclohexenones from carbohydrates by catalytic Ferrier rearrangement

Abstract: Conversion of hex-5-enopyranosides into substituted cyclohexanones (Ferrier rearrangement) was found to proceed efficiently with a catalytic amount of various mercury(II) salts at room temperature in a neutral solvent system. Among the mercury(II) salts tested, mercury(II) trifluoroacetate showed the highest activity. Four optically active cyclohexenones were prepared from hex-5-enopyranosides utilizing this method.

Chemistry, biology, and medicinal potential of narciclasine and its congeners.

Abstract: Ornamental flower growers know that placing a cut daffodil (a.k.a. narcissus) in a vase with other flowers has a negative effect on the quality of those flowers and significantly shortens their vase life. Furthermore, a common horticultural practice for the cultivation of narcissus flowers involves the introduction of cuts on the bulbs before immersing them into water. The mucilage that leaches out from the cuts is constantly removed by frequent changing of water and this leads to sprouting. These observations raise speculation that specific components in the mucilage of the narcissus bulbs may have powerful growth-inhibitory effects. Historical use of narcissus flowers, as well as at least thirty other plants of the Amaryllidaceae family, in folk medicine for the management of cancer1 speaks volumes to validate this conjecture. Indeed, powerful anticancer properties of Narcissus poeticus L. were already known to the Father of Medicine, Hippokrates of Kos (ca. B.C. 460–370), who recommended a pessary prepared from narcissus oil for the treatment of uterine tumors.2 His successors, the ancient Greek physicians Pedanius Dioscorides (ca. A.D. 40–90) and Soranus of Ephesus (A.D. 98–138) continued using this therapy in the first and second centuries A.D.3,4 In addition, the topical anticancer uses of extracts from this plant5,6 as well as from N. pseudonarcissus7–9 were recorded in the first century A.D. by the Roman natural philosopher Gaius Plinius Secundus, (A.D. 23–79), better known as Pliny the Elder.10 Even the Bible provides multiple references to the Mediterranean N. tazetta L., which has a long history of use against cancer.11 The applications of narcissus oil in cancer management continued in the middle ages in Chinese, North African, Central American and Arabian medicine.1,12 The uses of other genera of the Amaryllidaceae family were also common, e. g. Hymenocallis caribaea (L. emend Gawler) Herbert, utilized by early European medical practitioners for inflammatory tumors.13 More recently, the plants of the Amaryllidaceae have been under intense scrutiny for the presence of the specific metabolites responsible for the medicinal properties associated with this plant family. The study began in 1877 with the isolation of alkaloid lycorine from Narcissus pseudonarcissus14 and since then more than 100 alkaloids, exhibiting diverse biological activities, have been isolated from the Amaryllidaceae plants. Based on the present scientific evidence, it is likely that isocarbostyril constituents of the Amaryllidaceae, such as narciclasine, pancratistatin and their congeners, are the most important metabolites responsible for the therapeutic benefits of these plants in the folk medical treatment of cancer. Notably, N. poeticus L. used by the ancient Greek physicians, as was eluded before, is now known to contain some 0.12 g of narciclasine per kg of fresh bulbs.15 Continuing along this intriguing path, the focus of the present review is a comprehensive literature survey and discussion of the chemistry and biology of these compounds as specifically relevant to their potential use in medicine. The examination of the synthetic organic chemistry, more specifically the total synthesis efforts inspired by the challenging chemical structures of narciclasine, pancratistatin and their congeners, will be reduced to a minimum in view of the two very recent excellent reviews published on this subject.16,17

Kleider machen Leute: Heck-Reaktion im neuen Gewand†

Abstract: Die von Richard F. Heck Ende der sechziger Jahre entdeckte Palladium-katalysierte Kupplung von Aryl- und Alkenylhalogeniden mit Alkenen hat sich nach gelegentlichem Auf- und Abschwellen des darauf gerichteten Interesses in den letzten sechs Jahren nachhaltig gemausert. Durch geschickte Auswahl der Substrate und sorgfaltige Anpassung der Reaktionsbedingungen gelingen beeindruckende Sequenzen auch unterschiedlicher Reaktionstypen nicht nur nacheinander, sondern vielfach in einem einzigen Verfahrensschritt. Die mittlerweile etablierte Heck-Reaktion – und eine Reihe mit ihr mechanistisch verwandter Palladium-katalysierter Umwandlungen an Aren-, Alken- und Alkinderivaten – bietet ungezahlte Moglichkeiten, elegant und hochkonvergent komplexe Molekule aufzubauen; dabei bereiten Sauerstoff- und Stickstoffatome (mit Einschrankungen auch Schwefel- und Phosphoratome) in den Reaktionen keine Probleme. Das Spektrum der neueren Erfolge beginnt mit den chemo- und regioselektiven Einfachkupplungen hochfunktionalisierter Substrate mit unsymmetrisch mehrfach substituierten Reaktionspartnern. Es reicht allerdings viel weiter uber Kaskadenreaktionen mit Knupfung von drei, vier, funf oder gar acht neuen CC-Bindungen unter Bildung von oligofunktionellen und oligocyclischen Produkten von beeindruckender Molekulkomplexitat bis hin zum enantioselektiven Aufbau von anspruchsvollen Naturstoffmolekulen mit quartaren stereogenen Zentren, wie die Beispiele Crinan, Picrotoxinin, Morphin und viele mehr belegen. Zweifellos last sich schon heute die Heck-Reaktion aus dem Methodenarsenal der praparativen Organischen Chemie nicht mehr wegdenken; abzuwarten bleibt lediglich, wann sie Einzug in ein industrielles Produktionsverfahren halten wird.