Internal Seminar: Chemistry and Chemical Bioengineering & Marine Biophysics Unit

Please join us for our last Internal Seminar of the spring session on Friday May 20, from 17:00 to 18:00 in C700 (Lab3). This seminar features the Chemistry and Chemical Bioengineering Unit  (Fujie Tanaka) and the Marine Biophysics Unit (Satoshi Mitarai).

Chemistry and Chemical Bioengineering Unit (Fujie Tanaka)

Speaker : Dongxin Zhang

Title :  Synthesis of Molecules with Tetrasubstituted Carbon Centers via Functionalization of Carbonyl Compounds

Abstract : Synthesis of molecules bearing tetrasubstituted carbon centers is a challenge. Functionalized molecules with tetrasubstituted carbon centers are important as bioactive candidates and their synthons. We have found that DBU is a useful catalyst for fast, efficient, regioselective aldol reactions of a series of functionalized enolizable ketones with ketone electrophiles. In the presentation, we will discuss the DBU-catalyzed reactions to synthesize molecules bearing tetrasubstituted carbon centers.

(1) Synthesis of furanose spirooxindoles via DBU-catalyzed aldol reactions of a pyruvic aldehyde derivative with isatin

Spirooxindoles are important compounds as bioactive molecules and their leads. We have developed a route involving an aldol reaction of pyruvic aldehyde dimethyl acetal with isatins to concisely synthesize spirooxindole furanose derivatives. The DBU-catalyzed aldol reaction step was fast and gave the products in good yields in 15-30 min with complete regioselectivity

(2) Synthesis of aryl- and trifluoromethyl-substituted tertiary alcohols via DBU-catalyzed aldol reactions of aryl trifluoromethyl ketone acceptors.

Molecules bearing aryl- and trifluoromethylsubstituted tertiary alcohol moieties are important as bioactive molecules, enantiomer-discriminating reagents, and their synthons and building blocks. To concisely synthesize these molecules, we have developed aldol reactions of ketone donors with aryl trifluoromethyl ketone acceptors catalyzed by DBU. The reactions were relatively fast, and the products were obtained with perfect regioselectivity in good to high yields under mild conditions. Particularly, for the aldol products from the reactions of β-keto esters, the enantiomerically pure forms were obtained by the resolution of the enamines of the aldol products with a homochiral amine.

Marine Biophysics Unit (Satoshi Mitarai)

Speaker : Yuichi Nakajima

Title :  Species delimitation and genetic connectivity of broadcast-spawning and brooding corals in the Nansei Islands, Japan

Abstract : Estimation of species diversity and genetic connectivity is essential for management of coral populations and for understanding population maintenance systems. To estimate species diversity, corals must be classified genetically, because recent studies have demonstrated the existence of cryptic species. Maintenance of intraspecific populations depends upon larval dispersal resulting from sexual reproduction. Sexual reproduction of corals may be accomplished by either broadcast-spawning or brooding. We hypothesized that brooding corals maintain lower genetic connectivity among populations due to lower larval dispersal ability, compared with broadcast-spawning corals. We analyzed sequences of mitochondrial DNA (mtDNA) non-coding regions and multilocus microsatellite genotypes of the broadcast-spawning coral, Galaxea fascicularis, and the brooding coral, Seriatopora hystrix, in the Nansei Islands, Japan. Two nematocyst types are known in G. fascicularis, and these are significantly correlated with the length of the mtDNA sequence. Using microsatellites, significant genetic differentiation was detected between mtDNA types. We also found a third genetic cluster, and this unexpected mtDNA type may be a cryptic species of Galaxea. Though significant genetic differentiation within each putative species was found among four geographic regions, intraspecific genetic diversity and connectivity have been maintained, as in other marine broadcast-spawning species. Galaxea presumably has the potential to recover populations damaged by anthropogenic disturbances via both sexual and asexual reproduction. Three putative cryptic species of Seriatopora were identified at ten sites, each with a limited distribution, compared with the assumption that these are one species. We detected significant genetic differentiation between sites within each putative species. Additionally, only seven migrants from distant populations were genetically identified within putative species. These attributes probably reflect the low dispersal. Furthermore, fecundity may vary with population size, thereby influencing genetic differentiation among sites. Although sexual reproduction basically maintains all Seriatopora populations, some sites display decreased genetic diversity. Seriatopora populations in the Nansei Islands will probably suffer local extinction caused by local disturbances, unless there is substantial new recruitment from distant populations, which seems unlikely.

Refreshments will be served afterwards. We hope to see you there!