Oxidative transformation of tunichromes – Model studies with 1,2-dehydro-N-acetyldopamine and N-acetylcysteine

Catecholamine Derivatives as Novel Crosslinkers for the Synthesis of Versatile Biopolymers

Catecholamine metabolites are not only involved in primary metabolism, but also in secondary metabolism, serving a diverse array of physiologically and biochemically important functions. Melanin, which originates from dopa and dopamine, found in the hair, eye, and skin of all animals, is an important biopolymeric pigment. It provides protection against damaging solar radiation to animals. N-Acetyldopamine and N-β-alanyldopamine play a crucial role in the hardening of the exoskeletons of all insects. In addition, insects and other arthropods utilize the melanogenic process as a key component of their defense systems. Many marine organisms utilize dopyl peptides and proteins as bonding materials to adhere to various substrata. Moreover, the complex dopa derivatives that are precursors to the formation of the exoskeletons of numerous marine organisms also exhibit antibiotic properties. The biochemistry and mechanistic transformations of different catecholamine derivatives to produce various biomaterials with antioxidant, antibiotic, crosslinking, and gluing capabilities are highlighted. These reactivities are exhibited through the transient and highly reactive quinones, quinone methides, and quinone methide imine amide intermediates, as well as chelation to metal ions. A careful consideration of the reactivities summarized in this review will inspire numerous strategies for synthesizing novel biomaterials for future medical and industrial use.

Evaluation of the Physicochemical, Antioxidant, and Antibacterial Properties of Tunichrome Released from Phallusia nigra Persian Gulf Marine Tunicate

The aim of this study was to evaluate the physicochemical, nutraceutical, antioxidant, and antibacterial properties of tunichrome released from Persian Gulf tunicate (Phallusia nigra). For this purpose, molecular weight (SDS-PAGE), amino acid profile, chemical composition (GC-MS), mineral composition, functional groups (FTIR), total phenol content (TPC), total flavonoid content (TFC), antioxidant activity, and antimicrobial properties were investigated. The results showed that tunichrome contained a high amount of essential amino acids (i.e., Lys = 32.24 mg/100 g) and essential minerals. According to GC-MS results, tunichrome had different antioxidant and antimicrobial components. The TPC and TFC of tunichrome were 0.55 mg GA/g and 0.21 mg quercetin/100 g, respectively. Tunichrome showed higher antioxidant activity than ascorbic acid, and its radical scavenging activity values were increased from 30.28 to 82.08% by increasing concentration from 50 to 200 ppm. Inhibition zones of Staphylococcus aureus, Bacillus cereus, Salmonella enterica, and Escherichia coli O157:H7 were 14, 18, 17, and 15 mm, respectively. Moreover, the minimum inhibitory concentration values of tunichrome for S. aureus, Bacillus cereus, S. enterica, and E. coli O157:H7 were 1.17, 0.59, 0.59, and 1.17 mg/ml, respectively. The minimum bacterial concentrations were 2.34, 1.17, 1.17, and 2.34 mg/ml for S. aureus, Bacillus cereus, S. enterica, and E. coli O157:H7, respectively. These results showed that tunichrome of Phallusia nigra has excellent biological effects as a bioactive compound for food fortification.

Oxidative Oligomerization of DBL Catechol, a potential Cytotoxic Compound for Melanocytes, Reveals the Occurrence of Novel Ionic Diels-Alder Type Additions

The exposure of human skin to 4-(4-hydroxyphenyl)-2-butanone (raspberry ketone, RK) is known to cause chemical/occupational leukoderma. RK is a carbonyl derivative of 4-(4-hydroxyphenyl)-2-butanol (rhododendrol), a skin whitening agent that was found to cause leukoderma in skin of many consumers. These two phenolic compounds are oxidized by tyrosinase and the resultant products seem to cause cytotoxicity to melanocytes by producing reactive oxygen species and depleting cellular thiols through o-quinone oxidation products. Therefore, it is important to understand the biochemical mechanism of the oxidative transformation of these compounds. Earlier studies indicate that RK is initially oxidized to RK quinone by tyrosinase and subsequently converted to a side chain desaturated catechol called 3,4-dihydroxybenzalacetone (DBL catechol). In the present study, we report the oxidation chemistry of DBL catechol. Using UV–visible spectroscopic studies and liquid chromatography mass spectrometry, we have examined the reaction of DBL catechol with tyrosinase and sodium periodate. Our results indicate that DBL quinone formed in the reaction is extremely reactive and undergoes facile dimerization and trimerization reactions to produce multiple isomeric products by novel ionic Diels-Alder type condensation reactions. The production of a wide variety of complex quinonoid products from such reactions would be potentially more toxic to cells by causing not only oxidative stress, but also melanotoxicity through exhibiting reactions with cellular macromolecules and thiols.

Chemical Reactivities of ortho-Quinones Produced in Living Organisms: Fate of Quinonoid Products Formed by Tyrosinase and Phenoloxidase Action on Phenols and Catechols

Tyrosinase catalyzes the oxidation of phenols and catechols (o-diphenols) to o-quinones. The reactivities of o-quinones thus generated are responsible for oxidative browning of plant products, sclerotization of insect cuticle, defense reaction in arthropods, tunichrome biochemistry in tunicates, production of mussel glue, and most importantly melanin biosynthesis in all organisms. These reactions also form a set of major reactions that are of nonenzymatic origin in nature. In this review, we summarized the chemical fates of o-quinones. Many of the reactions of o-quinones proceed extremely fast with a half-life of less than a second. As a result, the corresponding quinone production can only be detected through rapid scanning spectrophotometry. Michael-1,6-addition with thiols, intramolecular cyclization reaction with side chain amino groups, and the redox regeneration to original catechol represent some of the fast reactions exhibited by o-quinones, while, nucleophilic addition of carboxyl group, alcoholic group, and water are mostly slow reactions. A variety of catecholamines also exhibit side chain desaturation through tautomeric quinone methide formation. Therefore, quinone methide tautomers also play a pivotal role in the fate of numerous o-quinones. Armed with such wide and dangerous reactivity, o-quinones are capable of modifying the structure of important cellular components especially proteins and DNA and causing severe cytotoxicity and carcinogenic effects. The reactivities of different o-quinones involved in these processes along with special emphasis on mechanism of melanogenesis are discussed.

Catechol thioethers with physiologically active fragments: Electrochemistry, antioxidant and cryoprotective activities

A number of asymmetrical thioethers based on 3,5-di-tert-butylcatechol containing sulfur atom bonding with physiologically active groups in the sixth position of aromatic ring have been synthesized and the electrochemical properties, antioxidant, cryoprotective activities of new thioethers have been evaluated. Cyclic voltammetry was used to estimate the oxidation potentials of thioethers in acetonitrile. The electrooxidation of compounds at the first stage leads to the formation of o-benzoquinones. The antioxidant activities of the compounds were determined using 2,2'-diphenyl-1-picrylhydrazyl radical (DPPH) assay, experiments on the oxidative damage of the DNA, the reaction of 2,2'-azobis(2-amidinopropane hydrochloride) (AAPH) induced glutathione depletion (GSH), the process of lipid peroxidation of rat liver (Wistar) homogenates in vitro, and iron(II) chelation test. Compounds 1-9 have greater antioxidant effectiveness than 3,5-di-tert-butylcatechol (CatH₂) in all assays. The variation of physiologically active groups at sulfur atom allows to regulate lipophilic properties and antioxidant activity of compounds. Thioethers 3, 4 and 7 demonstrate the combination of radical scavenging, antioxidant activity and iron(II) binding properties. The researched compounds 1-9 were studied as possible cryoprotectants of the media for cryopreservation of the Russian sturgeon sperm. Novel cryoprotective additives in cryomedium reduce significantly the content of membrane-permeating agent (DMSO). A cryoprotective effect of an addition of the catechol thioethers depends on the structure of groups at sulfur atom. The cryoprotective properties of compounds 3, 4 and 7 are caused by combination of catechol fragment, bonded by a thioether linker with a long hydrocarbon chain and a terminal ionizable group or with a biologically relevant acetylcysteine residue.

Marine natural products

Covering: January to December 2017This review covers the literature published in 2017 for marine natural products (MNPs), with 740 citations (723 for the period January to December 2017) referring to compounds isolated from marine microorganisms and phytoplankton, green, brown and red algae, sponges, cnidarians, bryozoans, molluscs, tunicates, echinoderms, mangroves and other intertidal plants and microorganisms. The emphasis is on new compounds (1490 in 477 papers for 2017), together with the relevant biological activities, source organisms and country of origin. Reviews, biosynthetic studies, first syntheses, and syntheses that led to the revision of structures or stereochemistries, have been included. Geographic distributions of MNPs at a phylogenetic level are reported.