Total Synthesis of Alternatamides B and D

Abstract The total synthesis of alternatamines B and D is outlined. Alternatamine B demonstrates moderate antibacterial activity across a broad spectrum of bacteria. Both alternatamines B and D feature an intriguing 5,6‐dibromoindole skeleton, derived from a four‐step sequence starting with 3,4‐dibromoaniline and achieving a total yield of 48 %. The key steps involve: (a) functional group modifications, including iodination, of 3,4‐dibromoaniline with two bromine substituents to obtain the Sonogashira precursor; (b) indole synthesis through Sonogashira coupling and 5‐ endo ‐dig cyclization; (c) carbon chain extension and introduction of the nitrogen atom at the C3 of the indole. Subsequently, the tryptamine analogue was coupled with an L‐leucine derivative through amide bond formation after deprotection, yielding alternatamide D. The first total synthesis of alternatamine B was also achieved by selectively introducing a bromine substituent at the C2 of the indole, employing optimal bromination conditions.