Total syntheses of [17]- and [18]dehydrodesoxyepothilones B via a concise ring-closing metathesis-based strategy: Correlation of ring size with biological activity in the epothilone series

A convergent ring-closing metathesis strategy has been employed for the highly concise syntheses of 10,11-dehydro-13,14-[17]desoxyepothilone B ([17]ddEpoB) and 10,11-dehydro-14,15-[18]desoxyepothilone B ([18]ddEpoB), which are 17- and 18-membered ring homologues of 10,11-dehydro-12,13-desoxyepothilone B ([16]ddEpoB or epothilone 490). We have demonstrated that the ring-closing metathesis (RCM) provides [17]ddEpoB or [18]ddEpoB with a high level of stereocontrol in the generation of the desired olefin in the products. These analogues were evaluated for antitumor activity. The results from the in vitro assays revealed that the [17]ddEpoB analogue is highly active against various tumor cell lines with a potency comparable to that of [16]ddEpoB. This is the first example of a 17-membered ring macrolactone epothilone that has retained its antitumor activity. In contrast, the biological data revealed that [18]ddEpoB is significantly less active than either [17]ddEpoB or the parent [16]ddEpoB.