Total synthesis of pyrrolizidines 223H′, 239K′, 265H′, and 267H′ found in Madagascan frogs (Mantella) and their affinities for nicotinic acetylcholine receptor

The total synthesis of pyrrolizidines 223H′, 239K′, 265H′, and 267H′ has been achieved starting from 1,5-hexadiene via a common synthetic intermediate 5. The affinity of 1–4 for nicotinic acetylcholine receptor was evaluated.