Common Gram-positive clinical pathogens are showing an increasing trend for resistance to conventional antimicrobial agents. New drugs with potent antibacterial activities are urgently needed to remediate this problem. Halogenated compounds isolated from several species of the red algae genus Laurencia were examined for their antibacterial activity against 22 strains of human pathogenic bacteria, 7 strains of which were antibiotic-resistant bacteria. Four phenolic sesquiterpenes and a polybrominated indole showed wide spectra of antibacterial activity against Gram-positive bacteria including methicillin-resistant Staphylococcus aureus (MRSA), penicillin-resistant Streptococcus pneumoniae, and vancomycin-resistant Enterococcus faecalis and E. faecium (VRE). In addition, laurinterol and allolaurinterol displayed potent bactericidal activity against three strains of MRSA at 3.13 microg mL(-1), and three strains of vancomycin-susceptible Enterococcus, at 3.13 microg mL(-1) and 6.25 microg mL(-1), respectively.

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The halogenated secondary metabolite constitution of four species of the red algal genus Laurencia (Rhodomelaceae) from southern Japan is reported. Laurencia composita Yamada from Tanegashima Island (Kagoshima Prefecture) bears five sesquiterpenoids (2,10-dibromo-3-chloro-α-chamigrene and 2,10-dibromo-3-chloro-9-hydroxy-α-chamigrene, in addition to prepacifenol epoxide, johnstonol and pacifenol, which are known in other populations of this species). Laurencia intricata Lamouroux from Chinzei (Saga Prefecture) and Oomura Bay (Nagasaki Prefecture) bear a C 15 acetogenin, okamurallene. Laurencia majuscula (Harvey) Lucas from Tanegashima Island produces three sesquiterpenoids, (Z )-10,15-dibromo-9-hydroxy-chamigra-1, 3(15),7(14)-triene, 10-bromo-7-hydroxylaurene and 10,11-dibromo-7-hydroxylaurene, corresponding to those of one of its chemical races. Laurencia venusta Yamada from Tanegashima Island produces two sesquiterpenoids, cupalaurenol and cyclolaurenol, which were known only from a sea hare, Aplysia dactylomela Rang. This strongly suggests that Aplysia consumes L. venusta and concentrates these halogenated compounds.

SUMMARY The halogenated secondary metabolite constitution of four species of the red algal genus Laurencia (Rhodomelaceae) from southern Japan is reported. Laurencia composita Yamada from Tanegashima Island (Kagoshima Prefecture) bears five sesquiterpenoids (2,10‐dibromo‐3‐chloro‐α‐chamigrene and 2,10‐dibromo‐3‐chloro‐9‐hydroxy‐α‐chamigrene, in addition to pre‐pacifenol epoxide, johnstonol and pacifenol, which are known in other populations of this species). Laurencia intricata Lamouroux from Chinzei (Saga Prefecture) and Oomura Bay (Nagasaki Prefecture) bear a C15 aceto‐genin, okamurallene. Laurencia majuscula (Harvey) Lucas from Tanegashima Island produces three sesquiterpenoids, (Z)‐10,15‐dibromo‐9‐hydroxy‐chamigra‐1, 3(15),7(14)‐triene, 10‐bromo‐7‐hydroxylaurene and 10,11‐dibromo‐7‐hydroxylaurene, corresponding to those of one of its chemical races. Laurencia venusta Yamada from Tanegashima Island produces two sesquiterpenoids, cupalaurenol and cyclolaurenol, which were known only from a sea hare, Aplysia dactylomela Rang. This strongly suggests that Aplysia consumes L. venusta and concentrates these halogenated compounds.

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