Evaluation of anti-quorum sensing and antimutagenic activity of 2,3-unsaturated and 2,3-dideoxyglucosides of terpene phenols and alcohols
Introduction
Herbs and spices are important food ingredients that impart aroma, colour, and taste to food preparations. While the volatile components in spices and herbs provide the aroma, the non-volatile resinous constituents impart the taste. Also, herbs and spices have been well-known for their antimicrobial, antimutagenic and antioxidant properties. These activities are often associated with the essential oil portion, whose oxygenated components are mainly terpene phenols and alcohols (Burt, 2004).
Quorum sensing (QS) is a regulatory bacterial cell to cell communication process involving production and response of diffusible signalling molecules, called autoinducers (AI) (Antunes, Ferreira, Buckner, & Finlay, 2010). These are produced at basal levels and accumulate as the bacterial population increases. Upon reaching a threshold concentration, the auto inducers bind to receptors inside the bacteria and activate or repress the target genes. This process is cell-density dependent (Antunes & Ferreira, 2009; Fuqua & Greenberg, 2002). Gram negative bacteria use either N-acyl homoserine lactone or molecules derived from S-adenosylmethionine (SAM) as AI's (Wei, Perez, Ng, Semmelhack, & Bassler, 2011). The Gram positive bacteria produce peptides, called the auto-inducing peptides (AIPs) as signaling molecules (Rutherford & Bassler, 2012). Quorum sensing is involved in a variety of physiological processes, including survival, virulence factors secretion, pathogenicity, biofilm formation, and also in food spoilage (Bai et al., 2011; Smith, Fratamico, & Novak, 2004). Hence disrupting the quorum-sensing circuit can play a significant role in controlling microbial gene expression related to food spoilage.
The 2,3-unsaturated glycosides, known as pseudo glycals, have been the cornerstones for many synthetic and mechanistic advances in carbohydrate chemistry. The oxygenated monoterpenes are lipophilic in nature, hence are required in higher concentration in food to exhibit antimicrobial activity. It could be advantageous to make them water-soluble by covalently bonding to a sugar moiety.
The phytochemicals in herbs and spices possess potent antimicrobial activity and therefore indicate the presence of potential anti-QS compounds (Krishnan, Yin, & Chan, 2012). The QS inhibitory activity of the phytochemicals is attributed to the similarity in chemical structure to those of QS signals, but also to their ability to interfere and degrade signal receptors (Teplitski, Mathesius, & Rumbaugh, 2011). The natural or synthetic molecules capable of quenching QS have been in intense focus of research for combating bacterial pathogenesis (Kalia, 2013). Since the phytochemicals are generally recognised as safe (GRAS), inhibition of QS by them offers an alternative to antibiotic-mediated approach to overcome the development of antibiotic resistance. Further, the antimutagenic potential of synthetic novel compounds was also reported (Manjunatha, Bettadaiah, Negi, & Srinivas, 2013; Santhosh Kumar, Srinivas, Negi, & Bettadaiah, 2013). Therefore, in the present study, we have analysed the anti-QS activity of the 2,3-dideoxy 1-O-glucoside derivatives of selected terpene phenols/alcohols and evaluated their antimutagenic potential.
Section snippets
Apparatus and materials
All the solvents and reagents used for the synthesis were of analytical grade. Terpene phenols, alcohols and palladium on carbon employed in the study were purchased from Sigma Aldrich Chemical Co. (St. Louis, MO, USA). H+ resin (Amberlite IR-120) used in the study was procured from Fluka Chemie, Switzerland. Petroleum ether, ethyl acetate, dimethyl sulphoxide and dry methanol were purchased from SpectroChem, Mumbai, India.
2,3-unsaturated and 2,3-dideoxyglucosides of terpene phenols and alcohols
The 2,3-unsaturated 1-O-glucoside acetates of selected phenols (1, 2)
QSI activity of terpene phenols/alcohols and their 2,3-unsaturated and 2,3-dideoxy 1-O-glucosides
The terpene phenols/alcohols and their compounds (Table 1) were effective at very low concentration (0.5 μmol/well) against both P. aeruginosa and C. violaceum as evidenced by the formation of halo inhibitory zones indicating their high QS Inhibitory activity. The halo-inhibitory zones demonstrated by the parent compounds and the derivatives were significantly different from each other (P ≤ 0.05) (Table 2). Among the tested bacterial strains, C. violaceum was more susceptible to compounds 1 and
Conclusions
The deoxyglucoside derivatives in general, exhibited better antiquorum sensing and antibacterial activity compared to the parent molecules as evidenced by a diminution of pigment production and lower MIC as well as MBC values. The 2,3-unsaturated 1-O-glucosides of carvacrol, thymol, fenchol and perillyl alcohol exhibited superior antimutagenic properties in comparison to parent molecules. The inhibition of mutagenicity demonstrated by the corresponding saturated analogues was more or less
Author contribution
D. James Bound conducted the experiments and wrote the draft. Pushpa S. Murthy helped with anti-quorum sensing studies and corrected the draft. P. Srinivas planned the chemical synthesis experiments and corrected the draft. P. S. Negi planned the antimutagenic studies and finalized the manuscript.
Declaration of competing interest
Authors declare no Conflict of Interest.
Acknowledgements
DJB is grateful to the Council of Scientific and Industrial Research (CSIR), New Delhi, India, for the fellowship.
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Present Address: Retired Chief Scientist, CSIR−CFTRI, 33, CFTRI Layout, Bogadi II Stage, Mysore 570 026, India.