thod. Samples were inoculated in marine media prepared with 100% natural sea water or 12826236 normal saline solution and amended with filtered cycloheximide and rifamycin, after autoclaving. Previous X-ray crystallography reports have shown that prenylated 4-hydroxybenzoyl moiety of aminocoumarin antibiotics has an important role in binding of the antibiotic to the gyrase in a mechanism that reduces the hydrophobic surface of the antibiotic as it wraps around the Pro74 of gyrase and folds back away from the solvent onto the coumarin ring leading to an increased interaction of the antibiotic and the bacterial gyrase. Compound 3, which only differs from 1 at position 4″ of the noviose moiety showed significant decrease in its inhibitory activity. Replacement of 
OMe group to OH group at position 4″of the noviose moiety decrease drastically the MIC by 64 fold in comparison with 1; this implies that 4″-OMe moiety is important for 26574517 the activity against MRSA. Previously published X-ray crystallographic data revealed that the extensive hydrogen bonding network between GyrB and novobiocin is contributed by not only by the 3″-carbamoyl moiety but also the 2″-OH and 4″-OMe moieties of the novoise ring. Specifically, 4″-OMe moiety forms a hydrogen bond with the Asn46 side chain of GyrB. This interaction may explain the decrease in MIC of compound 3 against MRSA and suggests that the replacement of OMe group at position 4″ of the noviose moiety with an OH group may weaken the interaction of 3 to the target site. Although the 3″-carbamoyl moiety of the novoise is crucial in the formation of hydrogen bonding network in the GyrB binding site, a change of the substituents at positions 4″ of novoise and position 5 of hydroxybenzoate ring as depicted in compound 6 produces analogs devoid of inhibitory activity against MRSA. In conclusion, the combined approach of phylogenetic and chemical analyses adopted in this study show that the community of Streptomyces from marine sediments of British Columbia, Canada is a highly prolific resource of antimicrobial natural products for bioprospecting. Actinomycetes growing on the isolation plates were transferred with sterile inoculating loops to MM1 medium until they are pure. Pure cultures were stored frozen in MM1 broth with 20% glycerol at -80C for long-term storage. were carried out in Applied Biosystems 3730 DNA Sequencer at the Nucleic Acid Protein Service Units, University of British Columbia. Comparison of the 16S rRNA gene sequences of the isolated actinomycete was determined by Basic Local Alignment Search Tool similarity searching GenBank nucleotide database. The 16S rRNA gene sequences of the related reference strains and other isolates were obtained from GenBank and aligned with ClustalX. The phylogenetic tree based on the highly variable -region of the 16S rRNA gene sequence to classify representatives and resolve relationship within the genus Streptomyces was used to construct a multiple alignment with the neighboring-joining method and a matrix of JukesCantor distances provided with the Mega5 software using 2,000 bootstrap replicates. Production and antimicrobial testing of isolates The pure cultures were grown in MM1 agar with 0.001 g of KBr and FeSO4.7H2O for 10 to 14 days at room temperature. The mature culture was harvested by Scopoletin cutting the biomass and the medium in small squares, then transferred to a small plastic bucket and soaked in EtOAc for 24 hours before extraction. The crude extract was partitione