Crinoids: ancient organisms, modern chemistry
Covering: 1877 to 2017
The ancestors of present-day crinoids are thought to be some of the earliest echinoderms, with fossil records dating back to the early Paleozoic Era (Ordovician Period, 505–440 million years ago). Their bright colours have been noted for over 100 years, and are attributed to a series of polyketide-derived pigments. Some crinoid metabolites display a range of biological activities, including cytotoxicity and fish anti-feedant activity. This review is divided into two parts. Part 1 is encyclopedic in scope, collating information on the >50 known metabolites isolated from crinoids, including their taxonomic source, collection location, chemical structure and biological activities. During the compilation of this data, two distinct themes emerged. Firstly, there is little variation in the class of metabolites produced by crinoids, irrespective of their species or geographic origin. Secondly, the complete and unambiguous assignment of crinoid metabolite structures has been, in many cases, a difficult task. This has been due to a lack of spectroscopic technology available in the past, the presence of proton-poor chemical structures, or both. Thus, Part 2 provides a critical discussion of crinoid chemistry, including the biosynthetic origin of crinoid pigments, as well as the pitfalls and solutions experienced by ourselves and other chemists when elucidating the chemical structures of crinoid metabolites.