Symphyocladins A-G: Bromophenol adducts from a Chinese marine red alga, Symphyocladia latiuscula

Chemical analysis of a Chinese collection of the marine red alga Symphyocladia latiuscula yielded five unprecedented bromophenol-aconitic acid adducts, symphyocladins A-E, together with a new example of a bromophenol-pyroglutamic acid adduct, symphyocladin F, a new example of a bromophenol-urea adduct, symphyocladin G, and the known methyl ester of cis-aconitic acid. The structures were assigned on the basis of detailed spectroscopic analysis, and were consistent with a plausible biosynthetic pathway linking these bromophenol natural products with a putative quinone methide intermediate. Symphyocladins A/B and C/D were isolated as inseparable 1:1 mixtures of E/Z isomers. A plausible mechanism for their facile equilibration during handling and storage is presented. The bromophenol-urea exhibits antifungal activity (MIC 10 μg/mL) against Candida albicans.