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Various halogenated organic compounds, originated from marine livings, have been well-known over five decades. Particularly, cyclic bromo-ether have attracted many chemists to study their existence, biogenetic syntheses and artificial syntheses, owing to their unique structures. Laurencia species produce eight-membered ethers as major products, although their syntheses by chemical procedures are generally difficult. These compounds are divided into laurenan and lauthisan groups based on the type of ring formation. The laurenan compounds are characteristic in respect of C6-S and C7-S configurations, while the lauthisan series haveR and R at the requisite positions. It has been proposed without any proof that the bromine atoms in the marine compounds could be introduced via bromo cationic species, generated by the two-electron oxidation of bromide ion with bromoperoxidase (BPO) and hydrogen peroxide. We studied on the enzymatic formation of these bromo-ethers, and found that both series of laurenan and lauthisan compounds could be biosynthesized directly from linear C15 compounds, laurediols. Herein, we mention our study of these natural products, and the recent studies around this field.

The term phytoalexin proposed by Muller and Borger in 1940 was recently revised as follows ; “phytoalexins are low molecular weight, antimicrobial compounds that are both synthesized by and accumulated in plants after exposure to microorganisms”. This definition has often been used as synonym of “stress compounds”. The present review describes survey of historical ground of isolation, structure, biosynthesis, biological activity, and role in plant-disease resistance of representative compounds identified as or called “phytoalexins”. Structural characteristics of “phytoalexins” and varieties of stresses causing formation of “phytoalexins” indicate that one of the most important studies to be done on phytoalexins is isolation and characterization of key enzymes leading to initial formation of “phytoalexins” and, if possible, endogeneous elicitors rather than exogeneous ones.

Naturally occurring spirovetivanes are divided into two classes based on the relative configuration between the C-4-C-14 and C-5-C-6 bonds : one class consists of a number of sesquiterpenes, represented by solavetivone and oxylubimin isolated as phytoalexins from diseased potato tubers, and possesses the trans configuration concerning the relevant bonds, while the other, including hinesol, β-vetivone, and others isolated from vetiver oil, takes the cis configuration.This review describes on recent advances in the synthetic studies on these spirovetivane sesquiterpenes.