SYNTHESIS OF NEW DIDEMNIN-B ANALOGS FOR INVESTIGATIONS OF STRUCTURE BIOLOGICAL-ACTIVITY RELATIONSHIPS

Modifications were introduced in the side chain of didemnin B to afford several analogs (1f-1j) for biological testing in order to identify the features responsible for the bioactivity of the natural products (1a-1c). To achieve our goal, two changes were made in the proline ring of the beta-turn side chain. Initially, a hydroxyl group was incorporated at the C-4 position of the ring to increase the polar nature of the molecule. Secondly, unsaturation was introduced at C-3 and C-4 to increase the rigidity of the ring and to provide a site for tritiation to follow the drug pathway in biological systems. Improvements were also introduced in the macrocycle construction to produce gram quantities of this unit (1d) for the preparation of the planned analogs. The linear precursor to the macrocycle was oxidized more effectively with 1,1,1-triacetoxy-1,1-dihydro-1,2-benziodoxol-3(1H)-one (Dess-Martin periodinane reagent), and cyclization yields were increased substantially by using a new coupling reagent, pentafluorophenyl diphenylphosphinate (FDPP). (1H-1,2,3-benzotriazol-1-yloxy)tris(dimethylamino)phosphonium hexafluorophosphate (BOP) and pentafluorophenyl trifluoroacetate were also used to improve other coupling reactions.