Microcolin B, a potent new immunosuppressant isolated from blue-green alga Lyngbya majuscula off the Venezuelan coast, has been made using a methyl-directed asymmetric hydrogenation reaction with rhodium on alumina catalyst on lactone 4 for the synthesis of the key (R,R)-2,4-dimethyloctanoic acid fragment 1. A new, direct mixed imide formation reaction was also developed for the production of the unusual prolylpyrrolen-2-one 2 portion of microcolin. The pentafluorophenyl ester of CBZ-proline 5 was reacted with the lithium imidate of lactam 6, providing the mixed imide in 80% yield. Coupling of acid 1 with the N-terminus of the tripeptide, followed by coupling with pyrrolylproline 2, gave microcolin B. The new mixed-imide forming reaction was also applied to a formal total synthesis of microcolin A. The pentafluorophenyl ester of TBS-protected cis-hydroxyproline was coupled with lactam 6, and the resultant imide was converted to the key pyrrolylproline made previously for microcolin A.

Fiduxosin (1) has been under development at Abbott Laboratories for the treatment of benign prostatic hyperplasia. A convergent strategy required methodologies for preparation of an enantiomerically pure 3,4-cis-disubstituted pyrrolidine and a 2,3,5-trisubstituted thienopyrazine in a regiospecific manner. A [3+2] cycloaddition of an enantiopure azomethine ylide followed by a diastereoselective crystallization was employed to prepare the benzopyranopyrrolidine in high diastereomeric and enantiomeric purity. Conditions for reduction of an O-aryl lactone susceptible to epimerization were developed, and cyclization of the alcohol/phenol to the ether was accomplished in high yield. The thienopyrazine was prepared by condensation of methyl thioglycolate and a regiospecifically prepared 2-bromo-3-cyano-5-phenylpyrazine. Conditions for effective halogen substitutive deamination to prepare regiospecific trisubstituted pyrazines will be described.

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A preliminary safety evaluation of ACC2 inhibitor 1-(S) revealed serious neurological and cardiovascular liabilities of this chemotype. A systematic structure-toxicity relationship study identified the alkyne linker as the key motif responsible for these adverse effects. Toxicogenomic studies in rats showed that 1-(R) and 1-(S) induced gene expression patterns similar to that seen with several known cardiotoxic agents such as doxorubicin. Replacement of the alkyne with alternative linker groups led to a new series of ACC inhibitors with drastically improved cardiovascular and neurological profiles.

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