Total synthesis of (+)-calyculin A

A convergent asymmetric synthesis of the marine natural product calyculin A has been accomplished through the union of the two subunits comprising the C1-C25 and C26-C37 portions of the molecule. These fragments were constructed utilizing auxiliary-based asymmetric aldol, alkylation, hydroxylation, and Michael reactions to establish 10 of the 15 stereogenic centers, The remaining chirality was incorporated through internal asymmetric induction. Stereoselective Wittig coupling of the two fragments and subsequent deprotection provided synthetic calyculin A. The spectral properties of the synthetic material were in complete agreement with those of the natural material except for the optical rotation which was equal and opposite in sign to that of the natural material. The absolute configuration of (-)-calyculin A has thus been shown to be opposite to that illustrated in structure 1.