THE TOTAL SYNTHESIS OF SWINHOLIDE-A .4. SYNTHESIS OF SWINHOLIDE-A AND ISOSWINHOLIDE-A FROM THE PROTECTED MONOMERIC SECO ACID, PRE-SWINHOLIDE-A

Swinholide A and isoswinholide A were synthesised in 7 steps from the fully protected seco acid 4. Key steps include: (i) bimolecular acylation, 7 + 10 --> 12, (ii) selective hydrolysis of the methyl ester, 16 --> 17, and (iii) regioselective macrolactonisation, 17 --> 18. The monomeric lactone analogues 2 and 5 were prepared by regioselective macrolactonisation of the seco acid 6, where the ring size was controlled by variation of the reaction conditions.