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WHEN various acyclic sesqui-, and higher, terpenes are subjected to the controlled action of N-bromosuccinimide (NBS) in aqueous ethylene glycol methyl ether or tetrahydrofuran, terminal monohalogenohydrins are the major products formed in good ~i e l d . l -~ We now report that, in the case of methyl farnesate (I) there are produced concurrently the bicyclic bromo-esters (11) , arising by direct terminal oxidation and cyclization of the acyclic terpene, a process akin to that presumed to operate in the biogenesis of 3-hydroxylated polycyclic terpenes and steroid~.~*5 C02Me By chromatographic meansC02Me.

SignificanceAnadromous fishes are those that migrate from the ocean into freshwater to reproduce and need to orient toward a suitable spawning stream or risk leaving no offspring. These migrants are known to use olfactory cues to guide stream selection, but the cues’ identities are not known. Incidentally, it is well-known that stream-dwelling larval sea lampreys emit a pheromone that guides conspecific adults ascending freshwater streams. We identified this pheromone as a fatty-acid derivative that attracts migratory adults into the baited channel in a natural spawning stream. These results illustrate an olfactory mechanism whereby lampreys reliably identify and orient toward a proven spawning ground over a large spatial scale and implicate a potential strategy for sea lamprey control.

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