Effects of storage and extraction procedures on yields of lipophilic metabolites from the brown seaweeds Dictyota ciliolata and D. menstrualis

Investigations focused on the ecological roles of m a n n e secondary metabolltes have become common, but manne ecologists have rarely assessed how methodologies used in sample preparation affect the extractability and stablhty of secondary metabolites and, thus measurements of intraspeclflc and interspeclflc compound vanance We assessed vanous procedures for storing, drylng, and extracting samples of 2 chenllcally defended brown seaweeds Dictyota cillolata and D menstrualis These plants contain the diterpenoid alcohols pachydictyol A dictyol B acetate and dlctyol E that are relatively stable under all test conditions In contrast, the related diterpenoid dlaldehyde dictyodlal decomposed when plant tissues or crude extracts were stored at -25'C for 13 to 27 wk or when tissues or extracts were freeze-dned or subjected to high vacuum (CO 01 torr) methods that are commonly used in studies of marine chemical ecology The stabihty of dictyodial was specles-specdlc, degrading more in D cillolata than in D menstrual~s Dunng a few extractions, dictyodial reacted with methanol (MeOH) to yleld a n artdact resulting from the addition of 2 molecules of MeOH per molecule of dlctyodial A mlxture of 2 1 dlchloromethane (DCM) and MeOH tended to extract the lipophlhc secondary metabolites better than MeOH or DCM alone Metabolltes were also afforded some protection agalnst degradation when fresh tissue was submerged In 2 1 DCM MeOH dunng storage at -25'C Results of thls inveshgation lndlcate that storage, extraction, and quantlflcation methods need to be o p t m z e d for analyses of individual compounds and that even ldentlcal compounds can behave differently when they occur in different specles