Current Organic Chemistry - Volume 19, Issue 1, 2015

Tyrosinase (EC 1.14.18.1) is known to be the rate-limiting enzyme responsible for catalyzing the first two steps in the synthesis of melanin pigments that determine the coloring of hair, skin and eyes. Tyrosinase catalyzes two- sequence distinct bio-reactions in pigment productions: L-tyrosine to L-dopa (hydroxylation); and L-dopa to dopaquinone (oxidation). The inhibition of tyrosinase has been established as one of the major strategies to regulate the production of melanin and the inhibitors are used to treat hyper-pigmentation and other unwanted effects from melanogenesis. There are now a variety of medicaments inhibiting melanin synthesis to treat excess melanin production or hyper-pigmentation of human skin, including the usage of natural plant extracts or chemically synthesized compounds. Recently, due to an increasing emphasis on healthy concepts, attention has been drawn to the usage of naturally produced crude materials and drugs in cosmetics and pharmaceutical applications. In this review, we demonstrate melanogenic inhibitory factors such as flavonoids, stilbenes, simple phenolics, furans, triterpenes, alkaloids, and other synthetic compounds. The structure-activity relationships are classified in terms of their inhibition of tyrosinase functions and copper chelating activity.

Microbial lipase has been recognized as one of the important biocatalysts due to its widely diversified enzymatic properties and substrate specificities. With the increased awareness of environmental protection and cost issue, lipase- catalyzed reactions have been viewed as the sustainable replacement for the chemical-driven reactions used in manufacture of biochemical products, biopharmaceuticals, nutraceuticals, foods and agrochemicals. However, production of lipases derived from microbial origin would normally require an effort-intensive purification step owing to the complexity of culture broth and the necessity of retaining lipase’s bioactive state. A great variety of lipases from bacterial and fungal sources have been purified to homogeneity by using general purification strategies such as precipitation and chromatographic separation. As a whole, these traditional purification techniques are usually multi-steps, laborious, non-specific, operated at small scale and potentially unsatisfactory in term of purity level. Alternative purification methods are therefore being explored in order to improve the overall yield and reduce the processing time. Advances in the purification methods have greatly expanded the choices of selection in designing the highly specialized purification scheme for various microbial lipases. This review focuses on the application of aqueous two-phase system (ATPS) as an alternative bioseparation method used in the purification of lipase from microbial sources. Moreover, the integration of ATPS in bioprocessing units such as fermentation as well as other purification technique was also reviewed.

The pervasive exposure of the general public to chemicals found in cosmetic products underlines the importance of maintaining stringent safety evaluations of cosmetic ingredients. Cosmetics products are composed of many raw ingredient materials including fragrances, colors, thickeners, surfactants, foam agents, minerals, and preservatives. Whether the make-up substances are chemical, synthetic or natural resource, they may be a problem for human dermal skin. The eyelid skin is one of the thinnest skins in the body, emphasizing the dangers of percutaneous absorption of irritants and allergens, with human eye areas on the face being extremely sensitive. Due to the sensitive nature of the human eyelid skin and tear film, great consideration must be taken when determining the safety of chemicals used to formulate cosmetics applied in the periorbital region. Among the cosmetic products commonly used, mascara, eyeliner, and eyelash glue are designed to be applied on the rims of the eyelid. The close proximity that these products may be applied daily to the ocular surface brings about the concern of chemical safety and ocular health. In this review, selected chemicals commonly found in the mascara, eyeliner and eyelash glue, and their potential hazards to the skin of ocular surface were specifically evaluated using available data.

Many algal extracts or algal bioactive ingredients have potential in suppressing cancer or different biological mechanisms. We previously found that aqueous extracts of Gracilaria tenuistipitata (AEGT) contained abundant antioxidants with protective effects against several reactive oxygen species (ROS) related DNA damages and diseases. However, the properties of crude extracts may limit its further applications. The aim of this study was to investigate the antioxidant and chelating activities of different AEGT partitionates by liquid-liquid solvent partitioned extraction. Three different solvents-partitioned extracts of AEGT, namely ethyl acetate (AEGT-pEA), n-butanol (AEGT-pBuOH) and distilled water (AEGT-pW), were separated for evaluating its total phenol (TPC), total flavonoid content (TFC), its 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity, 2,2-azinobis (3-ethyl-benzothiazoline-6-sulfonic acid) (ABTS) radical scavenging, ferric reducing antioxidant power, and ferrous ion-chelating ability. The TPC, DPPH/ABTS radical scavenging, and reducing powers at low polarity solvent partitions (AEGT-pEA and AEGT-pBuOH) were significantly higher than those of AEGT and AEGT-pW (p < 0.0001). In contrast, AEGT-pEA and AEGT-BuOH exhibited significantly lower TFC than AEGT-pW and AEGT (p < 0.005). The AEGT-pEA has the highest chelating ability compared to other partitions. The DPPH/ABTS radical-scavenging, reducing, and chelating powers show a dose responsive manner. In conclusion, we found the liquid-liquid solvent partition can further separate the AEGT into several potential partitions with more abundant antioxidant property than that of AEGT without partitioning.

A remarkable example of the progress in metal-free oxidation is the development of oxidation with dioxiranes. The reactivity of these peroxides seems to be due to the tendency for easy electrophilic O-atom transfer to nucleophilic substrates. This has been applied in order to achieve high regio- and stereoselective epoxidation and oxyfunctionalizations of target molecules. This review addresses a new approach consisting of the application of homogeneous and heterogeneous dioxiranes isolated and generate in situ. This method has shown promise to contribute to resolving a well-recognized general problem in the organic synthesis to achieve efficient synthetic methods that take into account the fundamental principles of green chemistry.

Recent events related to the terrorist threats make it clear that real-time and on-site detection of explosives and chemical warfare agents (CWAs) are in an urgent demand. As an artificial mimic of natural receptors, molecularly imprinted polymers (MIPs) have already been utilized for the detection of hazardous materials due to their strong mechanical strength, flexibility, long-time storage and low cost. The MIP sensors show great promise for the selective and sensitive detection. This review aims to provide a consolidation of information relating to the integration of MIPs and electrochemical, surface acoustic and optical sensors, using the most important or recent illustrative examples.

Nafion-H®, a perfluoroalkanesulfonic acid resin has emerged as one of the promising and potential heterogeneous catalysts. It has been widely applied as a green, efficient and a recyclable heterogeneous solid acid catalyst in diverse organic synthesis. The present review highlights the significant advancements which have been made in the last few decades in the field of Nafion-H® catalyzed organic reactions of synthetic relevance. This review mainly focuses on the utility of Nafion-H® catalyst for construction of carbon-carbon, carbon-oxygen bonds, oxidation reactions, protection and deprotection of alcohols and carbonyl compounds, functional group transformations, synthesis of heterocycles, rearrangements and some functionalized derivatives of Nafion-H®.

In this work we report the first small and wide-angle X-Ray diffraction study (S-WAXS) of L-proline ester based ionic liquids, a family of chiral ionic liquids (CILs) with several potential useful applications. Along the synthetic pathway that was followed to obtain the already described systems in ultra-pure form, some new compounds were synthesized. Noteworthy differences were observed in the SAXS low Q peak positions trends between chloride and nitrate salts.