Hibarimicinone

Recently identified natural atropisomeric compounds with potential medicinal applications are presented. The ability of natural receptors to possess differential binding between atropisomers is an important factor when considering active and inactive atropisomeric drugs, and has required the development of new techniques for atropselective synthesis of desired targets. Advances in this field therefore have significant relevance to modern pharmaceutical and medicinal chemistry. The atropisomeric natural products discussed include hibarimicinone, flavomannins, talaromannins, viriditoxin, rugulotrosin A, abyssomicin C, marinopyrroles, dixiamycins, streptorubin B, ustiloxins A-F, haouamine A, bisnicalaterines, and tedarene B, all of which show significant potential as leads in antibiotic, antiviral and anticancer studies. The importance for the development of common practices regarding atropisomer recognition and classification is also emphasized.

The total synthesis of hibarimicinone, a potent v-Src tyrosine kinase inhibitor possessing thirteen stereogenic centers and an axial chirality, has been achieved. The key step to constructing the eight-ring skeleton was the double Michael-Dieckmann-type cyclization (Hauser annulation) using a thiolactone pseudo-dimer. These synthetic studies indicated the efficiency of the thiolactone-employed route to synthesize the multiply functionalized polycyclic compounds. The ABCD-ring moiety including the bridging ether was constructed by a strategy including oxidation of the C-ring hydroquinone and the subsequent transfer of the oxidation stage to the neighboring ring. The atropisomer of hibarimicinone was also synthesized to confirm the structure of the natural product.

Efforts toward the synthesis of the decalin ring system common to the hibarimicin shunt metabolite HMP-Y1 and parent aglycone hibarimicinone are reported herein. An intramolecular Diels-Alder cyclization rapidly generated the decalin framework. Two approaches toward completion of the AB decalin were vetted. Incorporation of a phenylsulfonyl leaving group β- to both a ketone and a γ-lactone followed by base-induced elimination of sulfinate led to the undesired α,β-unsaturated lactone. Methanolysis of the γ-lactone followed by elimination produced the unexpected bridged cyclic ether by way of an intramolecular oxy-Michael addition of the endo oriented C13 alcohol.