Calanolide → 12-Acetoxycalanolide A

Participants

Reaction Steps

12-Acetoxycalanolide A (2), [α]D=+20°, gave a parent ion by HREIMS at m/z 412.1825 daltons corresponding to a molecular formula of C24H28O6. Significant fragment ions were observed for M+-CH3 (m/z 397, 41%), M+-AcOH (m/z 352, 30%) and M+-AcOH—CH3 (m/z 337, 100%). The presence of an acetate group was suggested by a sharp 3H singlet in the 1H NMR spectrum at δ 2.10 and 13C NMR resonances at δ 21.2 (3H) and 170.7. The remaining 1H and 13C NMR signals for compound 2 were very similar to those recorded for calanolide A (1), except that the H12 resonance in compound 2 was shifted downfield to δ 5.97. This suggested that compound 2 was the 12-acetoxy derivative of calanolide A (1). The J10-11 (6.5 Hz) and J11-12 (6.0 Hz) couplings in compound 2 supported a pseudoaxial orientation of the chromanol ring protons. The slightly diminished chromanol proton couplings in compound 2 conceivably resulted from a slight twisting of the flexible chromanol ring. Further evidence for the proposed substituent configuration was provided by difference nOe enhancements of 2% measured between H10 and H12.

Provenance & Evidence