SYNTHESIS AND STRUCTURAL DETERMINATION OF (+/-)-NEPLANOCIN-F

Neplanocin F (2), a minor constituent of the family of neplanocin antibiotics, was synthesized as a racemate in 12 steps from cyclopentenone 3/4, which in turn was available from D-ribonolactone. The carbocyclic ring of neplanocin F corresponds to the allylic rearranged isomer of the biologically active agent neplanocin A. Regiospecific reduction of the racemic cyclopentenone 3/4 and protection of the resulting alpha-alcohol as a benzyl ether 6 produced, after removal of the isopropylidene moiety, a compound (7) having allylic and homoallylic secondary alcohol functionalities. Differences in the reactivity of these two secondary alcohols were successfully manipulated to prepare the homoallylic substituted azide 14, which was then reduced and converted to the desired adenine ring by conventional methods. The spectral properties of the synthesized material [(+/-)-neplanocin F] were identical to those of the natural product, except for its lack of optical rotation. X-ray crystallographic analysis helped corroborate the structure. In contrast to its bioactive isomer, neoplanocin A, neplanocin F was devoid of cytotoxicity and in vitro antiviral activity.