TOTAL SYNTHESIS AND BIOSYNTHESIS OF BIOACTIVE SUBSTANCES

Colorado State University-Fort Collins, Fort Collins CO

Investigators

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Abstract

DESCRIPITION: (Principal Investigator?s Abstract) In the first portion of this proposal, we plan to study the biosynthesis of the potent anti-cancer drug taxol (paclitaxel). Our short-term objectives are to synthesize in stable and radioisotopically-labeled form, the primary biosynthetic intermediates following the cyclization of geranylgeranyl pyrophosphate viataxadiene to the fully oxygenated taxol core structure. The long-term objectives of this program are to elucidate and target the slow (rate-limiting) steps in the biosynthetic pathway; in collaboration with Prof. Rodney Croteau of Washington State University, we propose to transform Taxussp. cell culture cells with cloned genes (from the Croteau lab) for the rate-limiting steps with the ultimate aim of boosting the yield of taxol produced by Taxussp. cell culture. The use of both total syntheses, semi-synthesis of natural taxoids concurrent with the isolation of labeled metabolites from cell-free microsomal extracts and Taxussp. cell cultures will be utilized to map the biosynthetic pathway to taxol. The second portion of this program is to fully elucidate the biosynthetic pathway from primary amino acids (L-isoleucine, L-proline L-glutamate and L-tryptophan) and mevalonate-derived isoprene moieties to the anthelmintic polycyclic indole alkaloids comprising the paraherquamides, brevianamides, marcfortine, sclerotamide, aspergamides and asperparalines. Experimental evidence has been obtained that the paraherquamide class of alkaloids is constructed by a key biological Diels-Alder cycloaddition reaction. Structural and stereochemical evidence strongly implicates enzyme-mediated pre-organization of the Diels-Alder substrate conformation as the key step in fashioning the bicyclo(2.2.2) ring system that is unique to this family of alkaloids. Stable and radioisotopically labeled biosynthetic intermediates will be synthesized and utilized to establish the entire biosynthetic pathway with emphasis on the step responsible for constructing the bicyclo(2.2.2) ring nucleus of this class of natural products. Biomimetic cycloaddition reactions will be studied to interpose the intrinsic facial bias of the cycloaddition reactions with the anti-selective stereochemistry observed in the brevianamide system and the syn-selective stereochemistry observed in the paraherquamide system. The asymmetric, stereocontrolled biomimetic total synthesis of the paralytic alkaloid asperparaline A will be pursued in parallel with studies to elucidate the bio synthesis of this agent with an emphasis on the mode of formation of the unique spirosuccinimide ring system. An outgrowth of the work on the prenylated tryptophan intermediates in the paraherquamide biosynthetic pathways had led to the discovery of new and potent cell cycle inhibitors related to the tryprostatins and cyclotryprostatins An asymmetric total synthesis of cyclotryprostatin D and several analogs will be pursued in collaboration with Dr. Osada of the RIKEN Institute to identify mechanistically novel and selective inhibitors of the mammalian cell cycle.