Secondary Metabolites Of Five Marine-Derived Actinomycetes: Structures And Bioactivities

Due to the special living environment, marine-derived actinomycetes possesscomplex and distinct metabolic capabilities, resulting in wide diversity of theirsecondary metabolites in chemical structure and biological activity. Among them,many valuable leading compounds were obtained for discovery of new antibiotics,and some had been selected for preclinical study. In order to search for metaboliteswith chemical novelty and outstanding biological activities, a study on marine-derivedactinomycetes was carried out. Studies include isolating and screening strains,purification and structural elucidation of the secondary metabolites, and preliminarybioactivities evaluation of some pure compounds.Comprehensive methods including sample pretreatment, selective medium,inhibitor selection were used and136actinomycetes were isolated from twevelmarine-derived soil samples. Applying chemical screen assays,103actinomyceteswere selected from288actinomycetes of our laboratory, which has enriched our TLCand HPLC fingerprint library. Using the bioactive screen,25antitumor strains wereobtained from the103actinomycetes. Actinomycetes CHQ-64, which was positive toboth PKS I and NRPS gene fragments, having anti-tumor activity and rich TLCthinlayer behavior and HPLC chromatogram characteristics, was selected as a mainexperimental strain by PKS I/NRPS/helogenase gene fragments assays, together withapplying activity and chemical screening. The strains CMN-1/CHQ-2/CHQ-25wereselected because of significant antitumor activity and Streptomyces sp. CMN-62wasfocus on its rich TLC thinlayer behavior and HPLC chromatogram characteristics.In all,70compounds were separated and purified, from the extracts of the5aimed strains, by means of solvent extraction, silica gel column, ODS-C18, SephadexLH20, PHPLC, and etc. From Streptomyces sp. CHQ-64,49compounds (1-49) were isolated; from Streptomyces sp. CMN-62,7compounds (50-56) were isolated; fromStreptomyces sp. CMN-1,8compounds (57-64) were isolated; from Streptomyces sp.CHQ-2,3compounds (65-67) were isolated; from Streptomyces sp. CHQ-25,4compounds (68-70) were isolated.Structures of the70compounds were respectively determined by theirphysico-chemical properties and spectral data (MS, IR, UV, CD, NMR, TDDFT ECDcalculations and X-ray). Among them there are7hybrid isoprenoids (1-6,43),6oxopolyenes (7-12),28alkaloids {including6pyrrole derivatives (13-18),5piericidinderivatives (43-47),3indolecarbazole derivatives (68-70) and other14alkaloids(25-32,37,39-41,55-56)},2polyketides (48-49),9cycloheximide-derivates (19-24,60-62),5benzol derivatives (33-36,54),4aminobenzoic acid glycosides derivatives(50-53),3γ-butyrolactone derivatives (57-59),3actinomycins (65-67) and otherstructural type compounds (38,63-64). Twenty-five compounds are new, including2hybrid isoprenoids (1-2) with a rare form of fused rings,4novel hybrid isoprenoids(3-5,43),6oxo polyenes (7-12),3alkaloids (14-15,40),2benzol derivatives (35-36),2polyketides (48-49),4aminobenzoic acid glycosides derivatives (50-53). In thestudy, we established the relative and absolute configurations of hybrid isoprenoids(1-5) by the combination of NOESY, X-Ray, CD, and TDDFT ECD calculations. Therelative and absolute configurations of oxo polyenes (7-12) and aminobenzoic acidglycosides (50-53) were determined by the combination of biosynthetic origin,conformational analysis, coupling constants, and mosher methods.In the bioactivities evaluation, with respect to the new skeleton class, compound2has a formyl group which showed the best cytotoxic activities against HCT-8andA549cell lines, with IC50values of6.96and4.88μM, respectively. For drimentines,compound4showed the best cytotoxic activities against HCT-8, Bel-7402, A549andA2780cell lines, with IC50values of2.81,1.38,1.01and2.54μM, respectively. Apatent application for drimentine G (4) had been filed for in China. The biologicalactivities of six polyene macrolides were evaluated by antifungal assay with Candidaalbicans, using nystatin as a positive control. Compound7showed pronounced antifungal activity against Candida albicans with MICs of25-50μM. Threeγ-butyrolactone derivatives (57-59) isolated from CMN-1showed quorum-sensingactivity. Among these,59showed the best quorum sensing activity.Summarily, this work obtained70compounds, including23new compounds, fromfive marine-derived actinomycetes. New compounds (1-2) represent a new condensedpentacyclic skeleton, in which the indole ring is fused with a sesquiterpene moiety.New compound12was a skipped-polyol polyene macrolide, with a tetrahydrofuranketal functionality, which is the first example in skipped-polyol polyene macrolides.New compound53was an aminobenzoic acid glycosides derivative with a rareskeleton. New compounds2and4showed significant antitumor activities, whilecompound7showed strong antimicrobial activities. Quorum sensing activities ofcompound59were reported. This study provides novel structures for marine naturalproduct chemistry and bioactive template for exploring new antitumor andanti-antifungal drugs. Forty-nine compounds, including19new compounds wereobtained from actinomycetes CHQ-64, which was selected by PKSI/NRPS/helogenase gene fragments assays, together with applying activity andchemical screening. All above results show that integrated screening can get moreaimed strains, identify quickly active strain with some biosynthesis gene and findsome compounds with special structures. It is indicated that thegene-activity-chemical integrated screening methods may reduce the high activity butold compounds in the separation of natural products and some extent get more aimedstrains, identify quickly active strain with some biosynthesis gene and find somecompounds with special structures. The results of this study provided someexperimental basis for further in-depth research in the field.