Rekha Devi Chakraborty

Guaiane sesquiterpenes from seaweed Ulva fasciata Delile and their antibacterial properties

Two new guaiane sesquiterpene derivatives, guai-2-en-10alpha-ol (1) and guai-2-en-10alpha-methanol (2), were chromatographically purified as major constituents of the CHCl3/CH3OH (1:1, v/v) soluble fraction of Ulva fasciata. Acetylation of 2 furnished guai-2-en-10alpha-methyl methanoate (3) with acetyl group at C11 position. The structures of the compounds were elucidated using one and two-dimensional NMR and mass spectrometric analysis. Compounds 2 and 3 exhibited significant inhibition to the growth of Vibrio parahaemolyticus with minimum inhibitory concentrations of 25 and 35 microg/mL, respectively. The electronegative C10 acetyl group with high polarisability (7.02x10(-24) cm3) in 3 appeared to withdraw electron cloud from substituted cycloheptyl ring and (R)-3-methylcyclohept-1-ene moiety, thus acting as the nucleophilic center of the molecule resulting in high bioactivity.

O-heterocyclic derivatives with antibacterial properties from marine bacterium Bacillus subtilis associated with seaweed, Sargassum myriocystum

The brown seaweed, Sargassum myriocystum associated with heterotrophic bacterium, Bacillus subtilis MTCC 10407 (JF834075) exhibited broad-spectra of potent antibacterial activities against pathogenic bacteria Aeromonas hydrophila, Vibrio vulnificus, and Vibrio parahaemolyticus. B. subtilis MTCC 10407 was found to be positive for polyketide synthetase (pks) gene, and therefore, was considered to characterize secondary metabolites bearing polyketide backbone. Using bioassay-guided fractionation, two new antibacterial O-heterocyclic compounds belonging to pyranyl benzoate analogs of polyketide origin, with activity against pathogenic bacteria, have been isolated from the ethyl acetate extract of B. subtilis MTCC 10407. In the present study, the secondary metabolites of B. subtilis MTCC 10407 with potent antibacterial action against bacterial pathogens was recognized to represent the platform of pks-1 gene-encoded products. Two homologous compounds 3 (3-(methoxycarbonyl)-4-(5-(2-ethylbutyl)-5,6-dihydro-3-methyl-2H-pyran-2-yl)-butyl benzoate) and 4 [2-(8-butyl-3-ethyl-3,4,4a,5,6,8a-hexahydro-2H-chromen-6-yl)-ethyl benzoate] also have been isolated from the ethyl acetate extract of host seaweed S. myriocystum. The two compounds isolated from ethyl acetate extract of S. myriocystum with lesser antibacterial properties shared similar structures with the compounds purified from B. subtilis that suggested the ecological and metabolic relationship between these compounds in seaweed-bacterial relationship. Tetrahydropyran-2-one moiety of the tetrahydropyrano-[3,2b]-pyran-2(3H)-one system of 1 might be cleaved by the metabolic pool of seaweeds to afford methyl 3-(dihydro-3-methyl-2H-pyranyl)-propanoate moiety of 3, which was found to have no significant antibacterial activity. It is therefore imperative that the presence of dihydro-methyl-2H-pyran-2-yl propanoate system is essentially required to impart the greater activity. The direct involvement of polarisability (Pl) with the target bioactivity in 2 implied that inductive (field/polar) rather than the steric effect (parachor) appears to be the key factor influencing the induction of antibacterial activity. The present work may have a footprint on the use of novel O-heterocyclic polyketide products from seaweed-associated bacterium for biotechnological, food, and pharmaceutical applications mainly as novel antimicrobial secondary metabolites.

On Plesionika quasigrandisChace, 1985 (Decapoda, Caridea, Pandalidae) from southwestern India

The recent development of commercial deep-sea fisheries in India has mainly been off the southern coast and is based on shrimps (Rajan et al., 2001; Kurup et al., 2008; Rajool Shanis et al., 2014b). One of the dominant species in these catches is a pandalid shrimp previously reported as “Parapandalus (or Plesionika) spinipes” (e.g., Suseelan & Mohamed, 1968; Suseelan, 1974; Rajan et al., 2001; Kurup et al., 2008; Rajool Shanis et al., 2012; with the genus Parapandalus Borradaile, 1899 now generally synonymized with Plesionika Bate, 1888 (see Chace, 1985; De Grave & Fransen, 2011). Rajool Shanis et al. (2014a, b) later showed that this name was a misidentification of Plesionika quasigrandis Chace, 1985, which has the ventral rostral teeth more densely packed as opposed to P. spinipes, where the dorsal rostral teeth are more densely packed (see Chace, 1985; Chan & Crosnier, 1991). Although P. quasigrandis is one of the most important deep-sea shrimps in India from a commercial point of view, no proper taxonomic account has been given for the Indian material. The present study provides detailed taxonomic information of P. quasigrandis from India, together with molecular barcoding data.