Y. Iitaka

Chemical studies on the oriental plant drugs—XXXIII : The absolute structures of paeoniflorin, albiflorin, oxypaeoniflorin and benzoylpaeoniflorin isolated from chinese paeony root

The absolute structure of paeoniflorin, a major principle of Chinese Paeony root (Paonia albiflora Pallas (Paeoniaceae)) was established as I and as shown in Chart 2 by the X-ray analysis of a bromo derivative (VI) of product K2 acetate (V). The absolute structures of the minor constituents, albiflorin (VII), oxypaeoniflorin (IX) and benzoylpaeoniflorin (X) were also established on the basis of the established structure of paeoniflorin.

Asymmetric total synthesis of natural (-)-and unnatural (+)-steganacin : Determination of the absolute configuration of natural antitumor steganacin

Abstract A virtually complete asymmetric control in the synthesis of 2,3-disubstituted butan-4-olide (10) was demonstrated by employing the butenolide (12) as the chiral acceptor for the conjugate 1,4-addition. Highly efficient asymmetric total synthesis of natural (-)- and unnatural (+)-steganacin was accomplished. The absolute stereostructure of natural antitumor steganain was determined to be 1.

Mechanistic aspects of asymmetric cis-dihydroxylation of olefins with osmium tetroxide employing a C2-symmetric chiral diamine

Abstract Stereochemical consideration of the efficient enantioselective oxidation of trans-stilbene employing a C2-symmetric chiral diamine (5) strongly indicates an organometallocycle (2) as a possible intermediate in the oxidation of olefins with osmium tetroxide.

Structure and chemistry of kidamycin

By means of chemical studies as well as an X-ray analysis of kidamycin (1a), an antitumor antibiotic produced by a Streptomyces species, we have elucidated its structure and stereochemistry. Kidamycin represents a new type of polycyclic C-glycosyl microbial metabolites.

Studies on fungal metabolites—XXXII: A renewed investigation on (−) flavoskyrin and its analogues

Abstract 1-Oxo-1,2,3,4-tetrahydroanthraquinone ( 4a ), and its 8-hydroxy-( 4b ) and 8-hydroxy-6- methyl ( 4c ) derivatives were dimerized to the compounds formulated as ( 6a ), ( 6b ) and ( 6e ), respectively. The structure of 6a was confirmed by X-ray crystallographic analysis. By the analogy with these dimers and NMR spectral analysis, a revised structure ( 7 ) was proposed for (−) flavoskyrin, a yellow metabolite of Penicillium islandicum NRRL 1175. A biosynthetic scheme involving Diels-Alder type cyclo-addition (π4s + π2s) was proposed for (−) flavoskyrin.

The structures of eumitrins A1, A2 and B, the yellow pigments of the lichen, Usnea baylegi (Stirt.) Zahlbr

Abstract The yellow pigments named eumitrins A 1 , A 2 and B were isolated from the lichen, Usnea bayleyi (Stirt.)Zahlbr. The modified bixanthone structures of these compounds were deduced mainly from their spectral data, and their absolute structures ( 2a , 3a and 4a ) were established on the basis of X-ray crystallographic analysis of a transformed product ( 6 ) of tribromo-eumitrin B ( 5 ).

Enantiospecific total synthesis of (-)-megaphone by a highly controlled consecutive 1,4- and 1,3-asymmetric induction

Abstract Enantiospecific total synthesis of (-)-megaphone ( 1 ) is reported. The key synthetic tactic is the use of (4 S )-2 Z -ethylidene-4-trityloxymethyl-butan-4-olide ( 6 ) to both establish the relative and absolute stereochemistry of the contiguous tertiary and quaternary carbon centers by a highly controlled 1,4- and 1,3-asymmetric induction and construct the 4-methoxy-6,6-dialkyl-cyclohexenone portion of 1 .