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In this study, the antibiotic enhancement and quorum sensing (QS) inhibition of allylpyrocatechol (APC) and methyl gallate (MG) isolated from leaves of Piper betle (betel) and leaf shoots of Anacardium occidentale (cashew), respectively, were compared. When applied with streptomycin and tested against Staphylococcus aureus and Pseudomonas aeruginosa, the effect of APC was additive while that of MG was synergistic. In terms of QS inhibition against Chromobacterium violaceum, both compounds were equally effective with violacein inhibition observed at concentrations of 60 μg/mL. We successfully increased the purity of APC in the methanol betel leaf extract from 13.2% to 31.5% w/w through solvent partitioning. This study is the first to document the anti-QS activity of APC, which is comparable to that of MG.

Biological macromolecules are naturally occurring large cellular components responsible for a wide array of functions necessary for the growth and survival of living organisms. They also possess various bioactivities such as antimicrobial, antioxidant, antitumor, antiviral, antiinflammatory, antiproliferative, and hypoglycemic activities. The growing interest in bioactive macromolecules as potential therapeutical drugs has driven scientists to further study the association between their chemical structures and corresponding functions/activities. This chapter aims to provide a short overview on the structural features influencing the bioactivities of several biological macromolecules, namely l -amino acid oxidases, lysostaphin and metallo-β-lactamase-like lactonase and chitosan. As observed in this chapter, establishing the structure–activity relationship (SAR) can often prove to be challenging for macromolecules given the complexity of the three-dimensional organization level of proteins and the branched chains of the carbohydrates. Nevertheless, certain structural features influencing the bioactivities of macromolecules have been identified and could help to accelerate their development and application in the biomedical field. Indeed, a comprehensive understanding of biomacromolecule SARs remains necessary as information inferred from these studies may be crucial to many aspects of drug discovery and development, whether it is for primary screening or lead optimization, as well as for the designing of synthetic derivatives with improved properties.

The search for new and novel drugs is never-ending. Despite advances in synthetic chemistry, nature nevertheless remains as an important resource for the drug discovery. For decades, a routine screening of ethnopharmacologically important plants, followed by chromatographic isolation has been the basis of bioprospecting. Recent advances in bioinformatics and in silico screening have further improved our rate and likelihood of finding medicinal metabolites. Multiple classes of naturally occurring plant secondary metabolites, such as polyphenols, terpenoids, and alkaloids have been proven to possess significant medicinal potentials including antioxidant, anti-allergic, anti-inflammatory, anticancer, antihypertensive, and antimicrobial activities. The compounds of interest are often used as a basis or inspiration for semisynthetic drugs with improved pharmacokinetic and pharmacodynamic parameters. However, when a new biologically active compound has been identified, further in vivo testing and clinical trials may not reflect results seen in vitro. As with any promising fields, pitfalls and drawbacks are inevitable; these include poor bioavailability and unknown pharmacodynamics/pharmacokinetics. The drug development is further complicated by other challenges, such as processing, formulation, scaling up, and intellectual property protection. This chapter aims to discuss on the prospects of plant metabolites leading to drug discovery, along with the process and outcomes of testing and the potential pitfalls or challenges faced by researchers and the pharmaceutical industry in this endeavour.