The total synthesis of a new platelet aggregation-inhibiting gamma-lactam PI-091 (1) gave a 1:1 diastereomeric mixture at the gamma-ketal carbon. The high-yielding aldol reaction of an appropriately protected 1,3,4-trihydroxy-4-methyldecan-2-one 42, prepared from D-glucose, with the kinetically generated enolate of 3-methyl-2-butanone provided 43. The resulting diastereomeric mixture of the aldol adduct 43 was converted to a 2,4-alkylated furan 45 via an intramolecular ketalization followed by dehydration. The addition of a singlet oxygen to the alpha-trimethylsilylated furan 48derived from 45 under photochemical conditions efficiently provided an alpha,gamma-dialkylated gamma-hydroxy gamma-lactone 47. The transformation of methyl ketal 52 prepared from 47 into gamma-hydroxy gamma-lactam 53 was achieved by exposure to liquid ammonia in MeOH. The total synthesis of 1 was achieved from 52 through the Dess-Martin periodinane oxidation of the secondary hydroxy group in the side chain. The present total synthesis revealed that the stereogenic carbon center in the side chain in natural 1 is S.
The present study included the development of a new evaluation form that encompasses symptoms of end-stage kidney disease to predict falls in dialysis patients.
We describe the total syntheses of natural pseurotins A and F2, inhibitors of chitin synthase, both of which possess an unusual 1-oxa-7-azaspiro[4.4]non-2-ene-4,6-dione ring system. The total syntheses of these spiro-hetereocyclic natural products feature: 1) a stereoselective preparation of two segments, i.e., a 2,3-dihydroxylated heptenal derivative and a highly functionalized γ-lactone, each from d-glucose, 2) the connection of the two segments via an aldol-type carbon–carbon bond formation, 3) spirocyclic ring formation from the aldol adduct through convenient 3(2H)-furanone formation, 4) the transformation of a spirocyclic γ-lactone into a γ-lactam hemiaminal derivative, and 5) conversion of the benzyl substituent in the γ-lactam ring into a benzoyl group via a cyclic enamide followed by m-CPBA oxidation in the final stage of the total synthesis. In the initial stage, the quaternary spiro-carbon center in the target molecules was efficiently constructed by a stereochemically exclusive vinyl Grignard addition to the d-glucose-derived 3-ulose. Furthermore, the preparation of the γ-lactone included a stereo- and regioselective Cu(I)-mediated benzyl Grignard addition to aldehyde. We have also completed the total synthesis of a structurally related novel angiogenesis inhibitor, azaspirene, using the analogous reaction sequence.
C(aryl)−C(O) bonds of aryl amides can be activated and added across alkenes with the aid of a nickel catalyst. This 1,2-carboaminocarbonylation reaction enables the dicarbofunctionalization of alkenes with an atom economy of 100%.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.