| Research Abstract |
In this project, GE3 and Polyoxypeptins (A and B), novel 19-membered cyclic hexadepsipeptide antibiotics from Streptcmyces strains and Papuamides (A and B), novel cyclodepsipeptides with anti HIV and cytotoxic activies from the marine sponge genus Theonellawere synthetically studied. Stereoselective synthesis of the acyl side chain segment of GE3 has been achieved by using Sharpless's asymmetric dihydroxylation and stereoselective Evan's and Paterson's aldol methodologies. Stereoselective synthesis of the acyl side chain segment of Polyoxypeptins has been carried out through regioselective opening of chiral 2,3-epoxyalcohol. (2R,3R)-and (2S, 3S)-Hydroxyleucines, components of the cyclodepsipeptides, were efficiently synthesized along with their diastereomers from the corresponding β-keto-α-amino acid ester through dynamic kinetic resolution using RuC_2(binap) catalyzed hydrogenation, Stereoselective synthesis of (2S,3R)-3-hydroxy-3-raethylproline (2), a component of polyoxypeptins, has been achieved by use of diastereoselective cyclization reaction using SmI_2 as a key step. (3S,4R)-3,4-Dimethy1-(S)-glutamine,a component Papuamides, was stereoselectively prepared from (S)-pyroglutamic acid. The stereostructure of natural dimethylglutamine was unambiguously confirmed to be (2S,3S,4R)-stereochemistry by comparisons of their spectra of the synthetic 3,4-dimethylpyroglutamic acid with the hydrolysate from the natural product. Β-Methoxytyrosine (β-OMeTyr) is a stereoundefined component of papuamides. For structural determination and total synthesis of papuamides, all stereoisomers of β-(MeTyr were stereoselectively prepared from (S)-and (R )-serine, respectively.
Further studies on final construction of the three cyclodepsipeptides are under investigation in this laboratory.
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