Synthetic conversion of bryostatin 2 to bryostatin 1 and related bryopyrans

Bryostatin 2 ( 1 a) has been converted to bryostatin 1 ( 1 e) and bryostatin 12 ( 1 i) by a selective protection and deprotection involving the C-26 hydroxyl group. The new bryostatins 1 g, 1 k, and 1 m were also prepared starting from bryostatin 2. The C-7 substituents of natural bryostatins 4 and 5 were revised from isovalerate → pivalate employing comparative 1 H and 13 C NMR studies of the semi-synthetic bryostatins 1 k and 1 m and the natural products. Key words: bryostatin 2 → 1, selective conversion, bryostatins 4 and 5, pivalates.