Prosurugatoxin, a neurotoxin having a selective affinity for ganglionic nicotinic receptors, was newly isolated from the toxic ivory shell (Babylonia japonica) together with Surugatoxin 3 and Neosurugatoxin 2 by Kosuge et al. and the structure has been proposed to be 1 on the basis of chemical transformation (1→3) and spectroscopic data. Concerning the recent progress on the chemistry of these metabolites, we will discuss the following subjects: 1) Synthesis of Prosurugatoxin 1. 2) Development of an alternative synthetic method toward prosurugatoxin analogs (4, 5, and related stereoisomers) and their mydriasis activities in mice. 3) Mechanistic studies on the ring transformation of 1 into 3 using model compounds.