The first synthesis of a lactam analogue of salicylihalamide A (1) is reported. A key step in the approach was a photochemical acylation coupling between amine 10 and dioxinone 9 to form the amide 19. Acetylation followed by RCM with Grubbs 1st generation catalyst gave the desired E-lactam 23 (E : Z ratio 87 : 13) as the major compound. Conversion of macrolactam 23 into the vinyl iodide 26 followed by Cu catalysed cross coupling with the diene amide 7 gave aza-salicylihalamide analogue 3 in good yield. This compound demonstrated potent activity against several human leukaemia cell lines.
An approach to the dihydrooxepino[4,3-b]pyrrole core of diketopiperazine natural products which utilizes a vinyl pyrrole epoxide Cope rearrangement was investigated. It was found that an ester substituent on the epoxide was essential for the [3,3]-rearrangement to occur. Density functional calculations with M06-2X provided explanations for the effects of the pyrrole and ester groups on these rearrangements.
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