Azastilbene analogs as tyrosinase inhibitors: new molecules with depigmenting potential

Design and synthesis of novel dihydropyridine- and benzylideneimine-based tyrosinase inhibitors

Tyrosinase (TYR) inhibitors are very significant as they inhibit enzyme tyrosinase activity, and its inhibition is vital for skin care, anticancer medication, and antibrowning of fruits and vegetables. This work presents a novel and economical route for the preparation of new synthetic tyrosinase inhibitors using amlodipine (4). The novel conjugates 6 (a-o) were designed, synthesized, and characterized by spectroscopic analyses, including Fourier transform infrared and low- and high-resolution mass spectroscopy. The purified compound 4 was refluxed with various aldehydes and ketones 5 (a-o) for 5-8 h in methanol at 60°C-90°C. This research modified the drug in a step-by-step manner to develop therapeutic properties as a tyrosinase inhibitor. The structures of synthesized ligands 6 (a-o) were established based on spectral and analytical data. The synthesized compounds 6 (a-o) were screened against tyrosinase enzyme. Kojic acid was taken as standard. All the prepared compounds 6 (a-o) have good inhibition potential against the enzyme tyrosinase. Compounds 6o, 6b, 6f, and 6k depicted excellent antityrosinase activity. Compound 6k, with an IC50 value of 5.34 ± 0.58 µM, is as potent as the standard kojic acid (IC50 6.04 ± 0.11 µM), standing out among all synthesized compounds 6 (a-o). The in silico studies of the conjugates 6 (a-o) were evaluated via PatchDock. Compound 6k showed a binding affinity score of 8,999 and an atomic contact energy (ACE) value of -219.66 kcal/mol. The structure-activity relationship illustrated that the presence of dihydropyridine nuclei and some activating groups at the ortho and para positions of the benzylideneimine moiety is the main factor for good tyrosinase activity. The compound 6k could be used as a lead compound for drug modification as a tyrosinase inhibitor for skin care, anticancer medication, and antibrowning for fruits and vegetables.

Aza- and Azo-Stilbenes: Bio-Isosteric Analogs of Resveratrol

Several series of natural polyphenols are described for their biological and therapeutic potential. Natural stilbenoid polyphenols, such as trans-resveratrol, pterostilbene and piceatannol are well-known for their numerous biological activities. However, their moderate bio-availabilities, especially for trans-resveratrol, prompted numerous research groups to investigate innovative and relevant synthetic resveratrol derivatives. This review is focused on isosteric resveratrol analogs aza-stilbenes and azo-stilbenes in which the C=C bond between both aromatic rings was replaced with C=N or N=N bonds, respectively. In each series, synthetic ways will be displayed, and structural sights will be highlighted and compared with those of resveratrol. The biological activities of some of these molecules will be presented as well as their potential therapeutic applications. In some cases, structure-activity relationships will be discussed.

A comprehensive review on tyrosinase inhibitors

Tyrosinase is a multi-copper enzyme which is widely distributed in different organisms and plays an important role in the melanogenesis and enzymatic browning. Therefore, its inhibitors can be attractive in cosmetics and medicinal industries as depigmentation agents and also in food and agriculture industries as antibrowning compounds. For this purpose, many natural, semi-synthetic and synthetic inhibitors have been developed by different screening methods to date. This review has focused on the tyrosinase inhibitors discovered from all sources and biochemically characterised in the last four decades.

Insights about resveratrol analogs against trypanothione reductase of Leishmania braziliensis: Molecular modeling, computational docking and in vitro antileishmanial studies

In this work, we combined molecular modeling, computational docking and in vitro analysis to explore the antileishmanial effect of some resveratrol analogs (ResAn), focusing on their pro-oxidant effect. The molecular target was the trypanothione reductase of Leishmania braziliensis (LbTryR), an essential component of the antioxidant defenses in trypanosomatid parasites. Three-dimensional structures of LbTryR were modeled and molecular docking studies of ResAn1-5 compounds showed the following affinity: ResAn1 > ResAn2 > ResAn4 > ResAn5 > ResAn3. Positive correlation was observed between these compounds' affinity to the LbTryR and the IC₅₀ values against Leishmania sp (ResAn1 < ResAn2 < ResAn4), which allows for TryR being considered an important target for them. As the compound ResAn1 showed the best antileishmanial activity, and docking studies showed its high affinity for NADP binding site (NS) of TryR, plus having been able to induce ROS production in L. braziliensis promastigotes treated, ResAn1 probably occupies NS interfering in the electron transfer processes responsible for the catalytic reaction. The in silico prediction of ADMET properties suggests that ResAn1 may be a promising drug candidate with properties to cross biological membranes and high gastrointestinal absorption, not violating Lipinski's rules. Ultimately, the antileishmanial effect of ResAn can be associated with a pro-oxidant effect which, in turn, can be exploited as an antimicrobial agent. Communicated by Ramaswamy H. Sarma.

Kojic Acid Peptide: A New Compound with Anti-Tyrosinase Potential

BACKGROUND

Kojic acid was used for decades in the cosmetic industry as an antimelanogenic agent. However, there are two major drawbacks of Kojic acid, one is cytotoxicity and second are instability on storage. These limitations led the scientist to synthesize the active Kojic acid peptides.

OBJECTIVE

In the present study, we synthesize and investigate the effect of five Kojic acid peptides to overcome the limitation of Kojic acid.

METHODS

The peptide was analyzed and purified by high-performance liquid chromatography and matrix-assisted laser desorption ionization time of flight mass spectroscopy. Further, the tyrosinase activities of the Kojic acid and Kojic acid peptides were compared. The toxicity was measured and the melanin content is recorded in B16F10 mouse melanoma cells.

RESULTS

Maximum tyrosinase activity was measured by Kojic acid peptides. Therefore, Kojic acid peptides were subjected to melanin assay and cytotoxicity assay and finally the stability of the Kojic acid peptide was measured.

CONCLUSION

It was observed that this newly synthesized Kojic acid peptide is stable and potent to inhibit the tyrosinase activity and melanin content of B16F10 mouse melanoma cells without exhibiting cell toxicity. Together, these preliminary results suggest that a further exploration is being needed to establish Kojic acid peptide as antimelanogenic agent.

Synthesis of conjugated bile acids/azastilbenes as potential antioxidant and photoprotective agents

A series of 14 bile acids/azastilbenes conjugates (1a-g and 2a-g) was prepared through the condensation of bile amides (1 and 2) and aromatic aldehydes. The newly synthesized conjugates were evaluated in vitro for their antioxidant and photoprotective activities. Six compounds (1, 1a, 1b, 2, 2a and 2b) showed promising antioxidant activity with IC50 values of 19.60-31.83 μg mL(-1). The synthesized compounds presented a varied photoprotection profile, with the SPF ranging from 2 to 9. Among the 16 compounds tested for the protection against UVB sunrays, 3 compounds (2c, 2e and 2g) presented more significant protection than resveratrol and the free azastilbene 3; while the UVAPF increased from 2 in resveratrol and 5 in 3 to 5-11 in the majority of the conjugates.

Down-regulation of tyrosinase, TRP-1, TRP-2 and MITF expressions by citrus press-cakes in murine B16 F10 melanoma

OBJECTIVE

To investigate the suitability of citrus-press cakes, by-products of the juice industry as a source for the whitening agents for cosmetic industry.

METHODS

Ethylacetate extracts of citrus-press cakes (CCE) were examined for their anti-melanogenic potentials in terms of the inhibition of melanin production and mechanisim of melanogenesis by using Western Blot analysis with tyrosinese, tyrosinase-related protein-1 (TRP-1), TRP2, and microphthalmia-associated transcription factor (MITF) proteins. To apply the topical agents, citrus-press cakes was investigated the safety in human skin cell line. Finally flavonoid analysis of CCE was also determined by HPLC analysis.

RESULTS

Results indicated that CCE were shown to down-regulate melanin content in a dose-dependent pattern. The CCE inhibited tyrosinase, TRP-2, and MITF expressions in a dose-dependent manner. To test the applicability of CCE to human skin, we used MTT assay to assess the cytotoxic effects of CCE on human keratinocyte HaCaT cells. The CCE exhibited low cytotoxicity at 50 µg/mL. Characterization of the citrus-press cakes for flavonoid contents using HPLC showed varied quantity of rutin, narirutin, and hesperidin.

CONCLUSIONS

Considering the anti-melanogenic activity and human safety, CCE is considered as a potential anti-melanogenic agent and may be effective for topical application for treating hyperpigmentation disorders.

Synthesis, characterization and biological evaluation of paeonol thiosemicarbazone analogues as mushroom tyrosinase inhibitors

A series of hydroxy- and methoxy-substituted paeonol thiosemicarbazone analogues were synthesized as potential tyrosinase inhibitors and their inhibitory effects on mushroom tyrosinase and inhibitory mechanism were evaluated. Paeonol thiosemicarbazone analogues have been found exhibiting more remarkable inhibition than their indexcompounds on mushroom tyrosinase. Among them, compound 2,4-dihydroxy acetophenone-4-phenyl-3-thiosemicarbazone (d1) had the most potent inhibition activity with the IC50 value of 0.006 ± 0.001 mM, displayed as a reversible competitive inhibitor. The inhibitory ability of o- or p-substituted acetophenone thiosemicarbazones was: di-substituted acetophenone thiosemicarbazones>mono-substituted acetophenone thiosemicarbazones>non-substituted acetophenone thiosemicarbazones. Copper ions chelation assay explained that compound d1 exhibited competitive inhibition by forming a chelate with the copper ions at the catalytic domain of tyrosinase as well as indicate a 1.5:1 binding ratio of compound d1 with copper ions. In the fluorescence spectrum study, compound d1 behaved stronger fluorescence quenching on tyrosinase towards d1-Cu(2+) complex, inhibiting tyrosinase mainly by means of chelating the two copper ions in the active site. The newly synthesized compounds may serve as structural templates for designing and developing novel tyrosinase inhibitors.