Chlorofusin: Total synthesis, stereochemical reassignment, determination of absolute configuration, and the synthesis of seven chromophore analogs.

摘要

Chlorofusin is a recently isolated, naturally occurring inhibitor of the p53-MDM2 interaction, whose structure is comprised of a densely functionalized azaphilone-derived chromophore linked through the terminal amine of ornithine to a nine residue cyclic peptide. In this thesis, details of the total synthesis of chlorofusin, resulting in the assignment of the absolute stereochemistry and reassignment of the relative stereochemistry of the complex chromophore are reported. Construction of the azaphilone serving as the chromophore precursor closely followed literature precedent. However, a new reaction entailing an activated iodine induced alpha-hydroxylation/N,O-spiroketalization was developed for the construction of the chromophore core. Incorporation of benzylamine and n-butylamine into the azaphilone afforded two model systems of the chromophore precursor. One-step iodine induced alpha-hydroxylation/ N,O-spiroketalization of the most reactive C8--C9 olefin of both model systems provided four racemic chromophore analogs of both series respectively. The relative stereochemistry of the chlorofusin chromophore was deduced by X-ray crystallography and spectral data comparison of the two model systems of the chromophore analogs with that of natural product. Resolution of the two enantiomers of the azaphilone using chiral HPLC followed by incorporation of the resulting two enantiomers with the Ndelta -amine of a protected ornithine-threonine dipeptide afforded two dipeptide adducts of the azaphilones, and subsequent alpha-hydroxylation/ N,O-spiroketalization provided all eight diastereomers of the fully elaborated chromophore-dipeptide conjugate. Comparison of the spectroscopic properties for these eight compounds with that reported for the natural product allowed for the full assignment of the (4R,8S,9 R)-stereochemistry of the chlorofusin chromophore. The natural, but stereochemically reassigned, diastereomer of the dipeptide conjugate was incorporated into a convergent total synthesis of chlorofusin, which confirmed the stereochemical reassignment and established its absolute stereochemistry. Similarly, the remaining seven diastereomers of the chromophore-dipeptide conjugates were individually incorporated into the 9-residue cyclic peptide of chlorofusin (4 steps each) providing all seven remaining possible chromophore diastereomers of the natural product.