Solid-phase synthesis of mimosine tetrapeptides and their inhibitory activities on neuraminidase and tyrosinase

Tripeptides conjugated with thiosemicarbazones: new inhibitors of tyrosinase for cosmeceutical use

The development of skin-care products is recently growing. Cosmetic formulas containing active ingredients with proven efficacy, namely cosmeceuticals, are based on various compounds, including peptides. Different whitening agents featuring anti-tyrosinase activity have been applied in the cosmeceutical field. Despite their availability, their applicability is often limited due to several drawbacks including toxicity, lack of stability, and other factors. In this work, we present the inhibitory effect on diphenolase activity of thiosemicarbazone (TSC)-peptide conjugates. Tripeptides FFY, FWY, and FYY were conjugated with three TSCs bearing one or two aromatic rings via amide bond formation in a solid phase. Compounds were then examined as tyrosinase and melanogenesis inhibitors in murine melanoma B16F0 cell line, followed by the cytotoxicity assays of these cells. In silico investigations explained the differences in the activity, observed among tested compounds. Mushroom tyrosinase was inhibited by TSC1-conjugates at micromolar level, with IC₅₀ lower than this for kojic acid, a widely used reference compound. Up to now, this is the first report regarding thiosemicarbazones conjugated with tripeptides, synthesised for the purpose of tyrosinase inhibition.

Antiviral Peptides as Anti-Influenza Agents

Influenza viruses represent a leading cause of high morbidity and mortality worldwide. Approaches for fighting flu are seasonal vaccines and some antiviral drugs. The development of the seasonal flu vaccine requires a great deal of effort, as careful studies are needed to select the strains to be included in each year's vaccine. Antiviral drugs available against Influenza virus infections have certain limitations due to the increased resistance rate and negative side effects. The highly mutative nature of these viruses leads to the emergence of new antigenic variants, against which the urgent development of new approaches for antiviral therapy is needed. Among these approaches, one of the emerging new fields of "peptide-based therapies" against Influenza viruses is being explored and looks promising. This review describes the recent findings on the antiviral activity, mechanism of action and therapeutic capability of antiviral peptides that bind HA, NA, PB1, and M2 as a means of countering Influenza virus infection.

5-Amino-3-methyl-Isoxazole-4-carboxylic Acid as a Novel Unnatural Amino Acid in the Solid Phase Synthesis of α/β-Mixed Peptides

The hybrid peptides consisting of α and β-amino acids show great promise as peptidomimetics that can be used as therapeutic agents. Therefore, the development of new unnatural amino acids and the methods of their incorporation into the peptide chain is an important task. Here, we described our investigation of the possibility of 5-amino-3-methyl-isoxazole-4-carboxylic acid (AMIA) application in the solid phase peptide synthesis. This new unnatural β-amino acid, presenting various biological activities, was successfully coupled to a resin-bound peptide using different reaction conditions, including classical and ultrasonic agitated solid-phase synthesis. All the synthesized compounds were characterized by tandem mass spectrometry. The obtained results present the possibility of the application of this β-amino acid in the synthesis of a new class of bioactive peptides.

Influence of the Nonprotein Amino Acid Mimosine in Peptide Conformational Propensities from Novel Amber Force Field Parameters

Mimosine is a nonprotein amino acid derived from plants known for its ability to bind to divalent and trivalent metal cations such as Zn²⁺, Ni²⁺, Fe²⁺, or Al³⁺. This results in interesting antimicrobial and anticancer properties, which make mimosine a promising candidate for therapeutic applications. One possibility is to incorporate mimosine into synthetic short peptide drugs. However, how this amino acid affects the peptide structure is not well understood, reducing our ability to design effective therapeutic compounds. In this work, we used computer simulations to understand this question. We first built parameters for the mimosine residue to be used in combination with two classical force fields of the Amber family. Then, we used atomistic molecular dynamics simulations with the resulting parameter sets to evaluate the influence of mimosine in the structural propensities for this amino acid. We compared the results of these simulations with homologous peptides, where mimosine is replaced by either phenylalanine or tyrosine. We found that the strong dipole in mimosine induces a preference for conformations where the amino acid rings are stacked over more extended conformations. We validated our results using quantum mechanical calculations, which provide a robust foundation for the outcome of our classical simulations.

Amino Acid Based Antimicrobial Agents - Synthesis and Properties

Structures of several dozen of known antibacterial, antifungal or antiprotozoal agents are based on the amino acid scaffold. In most of them, the amino acid skeleton is of a crucial importance for their antimicrobial activity, since very often they are structural analogs of amino acid intermediates of different microbial biosynthetic pathways. Particularly, some aminophosphonate or aminoboronate analogs of protein amino acids are effective enzyme inhibitors, as structural mimics of tetrahedral transition state intermediates. Synthesis of amino acid antimicrobials is a particular challenge, especially in terms of the need for enantioselective methods, including the asymmetric synthesis. All these issues are addressed in this review, summing up the current state‐of‐the‐art and presenting perspectives fur further progress.

Do Uncommon Plant Phenolic Compounds Have Uncommon Properties? A Mini Review on Novel Flavonoids

Unique plants and their properties, once considered synonymous to medicine, remain a potent source for new compounds in modern science. Plant polyphenols and natural products continue to be investigated for effective treatments for the most persistent of human ailments. In this review, fifty novel plant phenolic compounds have been compiled and briefly described from the previous five years. Select compounds and notable plant species from genus Morinda and Sophora are further expanded on. Traditional medicine plants often contain rich and diverse mixtures of flavonoids, from which rare compounds should receive attention. The bioactivity of crude plant extracts, purified compounds and mixtures can differ greatly, requiring that these interactions and mechanisms of action be investigated in greater detail. Novel applications of uncommon natural products, namely mimosine and juglone, are explored within this review. The 2019 coronavirus pandemic has resulted in abrupt spike of related scientific publications: speculation is made regarding plant natural products and future of antiviral drug discovery.

K-Nearest Neighbor and Random Forest-Based Prediction of Putative Tyrosinase Inhibitory Peptides of Abalone Haliotis diversicolor

Skin pigment disorders are common cosmetic and medical problems. Many known compounds inhibit the key melanin-producing enzyme, tyrosinase, but their use is limited due to side effects. Natural-derived peptides also display tyrosinase inhibition. Abalone is a good source of peptides, and the abalone proteins have been used widely in pharmaceutical and cosmetic products, but not for melanin inhibition. This study aimed to predict putative tyrosinase inhibitory peptides (TIPs) from abalone, Haliotis diversicolor, using k-nearest neighbor (kNN) and random forest (RF) algorithms. The kNN and RF predictors were trained and tested against 133 peptides with known anti-tyrosinase properties with 97% and 99% accuracy. The kNN predictor suggested 1075 putative TIPs and six TIPs from the RF predictor. Two helical peptides were predicted by both methods and showed possible interaction with the predicted structure of mushroom tyrosinase, similar to those of the known TIPs. These two peptides had arginine and aromatic amino acids, which were common to the known TIPs, suggesting non-competitive inhibition on the tyrosinase. Therefore, the first version of the TIP predictors could suggest a reasonable number of the TIP candidates for further experiments. More experimental data will be important for improving the performance of these predictors, and they can be extended to discover more TIPs from other organisms. The confirmation of TIPs in abalone will be a new commercial opportunity for abalone farmers and industry.

Biochemistry of plants N-heterocyclic non-protein amino acids

Plants catalyze the biosynthesis of a large number of non-protein amino acids, which are usually toxic for other organisms. In this review, the chemistry and metabolism of N-heterocyclic non-protein amino acids from plants are described. These N-heterocyclic non-protein amino acids are composed of β-substituted alanines and include mimosine, β-pyrazol-1-yl-L-alanine, willardiine, isowillardiine, and lathyrine. These β-substituted alanines consisted of an N-heterocyclic moiety and an alanyl side chain. This review explains how these individual moieties are derived from their precursors and how they are used as the substrate for biosynthesizing the respective N-heterocyclic non-protein amino acids. In addition, known catabolism and possible role of these non-protein amino acids in the actual host is explained.

Naturally occurring and synthetic peptides: Efficient tyrosinase inhibitors

Tyrosinase is a copper-containing enzyme involved in the biosynthesis of melanin pigment, which is the most important photo protective agent against skin photo carcinogenesis. Excess production of melanin causes hyperpigmentation leading to undesired browning in human skin, fruits, and vegetable as well as plant-derived foods. Moreover, the role of tyrosinase in the onset and progression of various diseases such as cancers, Alzheimer's, and Parkinson diseases has been well documented in the literature. In this respect, tyrosinase inhibitors have been in the center of attention particularly as the efficient skin whitening agents. Among a wide range of compounds possessing anti-tyrosinase activity, peptides both natural and synthetic derivatives have attracted attention due to high potency and safety.

Synthesis and Mass Spectrometry Analysis of Mimosine-Containing Peptides

Non-proteinogenic amino acids are widely explored group of compounds due to their chemical properties and great potential of application in the combinatorial chemistry, medicinal investigation etc. Therefore the synthetic methods of their incorporation to the peptide chain are required. l-Mimosine, (S)-α-amino-β-(3-hydoxy-4-oxo-1,4-dihydropyridin-1-yl)-propanoic acid), is a plant amino acid, known to induce apoptosis in human pancreatic cancer xenografts. Here we present our investigations on the synthesis of mimosine-containing peptide and their ESI-MS/MS analysis. We successfully applied Fmoc-protected mimosine a with a free hydroxy ketone group for efficient peptide synthesis in the presence of HATU as a coupling reagent without the formation of side products. Additionally the tandem mass spectrometry analysis revealed the characteristic loss of the heterocyclic ring from mimosine residue side chain. The described method allows insertion of mimosine residue at any endo-position within a peptide sequence. The obtained results may be useful in the synthesis and mass spectrometry analysis of various mimosine-containing peptides.

Metal self-assembly mimosine peptides with enhanced antimicrobial activity: towards a new generation of multitasking chelating agents

Mimosine is a non-protein amino acid that can be used as a building block in peptides with metal coordination ability.

In silico design of mimosine containing peptides as new efficient chelators of aluminum

The design of new and efficient chelators that can remove aluminium(iii), a metal with increasing recognition as a potential toxic agent, from biological systems is an area of high therapeutic relevance. In the present paper, we present an extensive computational study of a new promising type of these chelators based on mimosine containing peptides. The reason to choose mimosine is that the sidechain of this residue is similar to deferiprone, a ligand known to tightly interact with highly-valent metals, and in particular with Al(iii). In this article we analyze systematically, using a combination of methods that include QM/MM MD simulations, how the size and sequence of the polypeptides can alter the fundamental binding patterns to aluminum, in comparison with the binding to deferiprone. Particular attention is given towards the identification of the smallest peptide that interacts efficiently with aluminum, since polypeptide size is a fundamental factor to allow a given polypeptide to efficiently cross the cell membrane. The results indicate that the longest peptides, with 8 or 9 amino acids, show no difficulties interacting with Al(iii) in an optimum arrangement. By contrast, when the peptide contains five or six amino acids Al(iii) is pentacoordinated, reducing the stability of the resultant complex. In summary, our study demonstrates that the mimosine containing peptides can efficiently coordinate highly valent metals such as Al(iii), with a subtle dependence of the binding on the specific chain-lengths of the polypeptide. We believe that the present study sheds light on the adequacy of this new type of chelator towards aluminum binding.

A novel chelator of aluminum is presented, a peptide containing three mimosine residues.

A Novel Natural Influenza A H1N1 Virus Neuraminidase Inhibitory Peptide Derived from Cod Skin Hydrolysates and Its Antiviral Mechanism

In this paper, a novel natural influenza A H1N1 virus neuraminidase (NA) inhibitory peptide derived from cod skin hydrolysates was purified and its antiviral mechanism was explored. From the hydrolysates, novel efficient NA-inhibitory peptides were purified by a sequential approach utilizing an ultrafiltration membrane (5000 Da), sephadex G-15 gel column and reverse-phase high-performance liquid chromatography (RP-HPLC). The amino acid sequence of the pure peptide was determined by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICR-MS) was PGEKGPSGEAGTAGPPGTPGPQGL, with a molecular weight of 2163 Da. The analysis of the Lineweacer–Burk model indicated that the peptide was a competitive NA inhibitor with Ki of 0.29 mM and could directly bind free enzymes. In addition, docking studies suggested that hydrogen binding might be the driving force for the binding affinity of PGEKGPSGEAGTAGPPGTPGPQGL to NA. The cytopathic effect reduction assay showed that the peptide PGEKGPSGEAGTAGPPGTPGPQGL protected Madin–Darby canine kidney (MDCK) cells from viral infection and reduced the viral production in a dose-dependent manner. The EC₅₀ value was 471 ± 12 μg/mL against H1N1. Time-course analysis showed that PGEKGPSGEAGTAGPPGTPGPQGL inhibited influenza virus in the early stage of the infectious cycle. The virus titers assay indicated that the NA-inhibitory peptide PGEKGPSGEAGTAGPPGTPGPQGL could directly affect the virus toxicity and adsorption by host cells, further proving that the peptide had an anti-viral effect with multiple target sites. The activity of NA-inhibitory peptide was almost inactivated during the simulated in vitro gastrointestinal digestion, suggesting that oral administration is not recommended. The peptide PGEKGPSGEAGTAGPPGTPGPQGL acts as a neuraminidase blocker to inhibit influenza A virus in MDCK cells. Thus, the peptide PGEKGPSGEAGTAGPPGTPGPQGL has potential utility in the treatment of the influenza virus infection.

Multi-Omics Studies towards Novel Modulators of Influenza A Virus-Host Interaction

Human influenza A viruses (IAVs) cause global pandemics and epidemics. These viruses evolve rapidly, making current treatment options ineffective. To identify novel modulators of IAV–host interactions, we re-analyzed our recent transcriptomics, metabolomics, proteomics, phosphoproteomics, and genomics/virtual ligand screening data. We identified 713 potential modulators targeting 199 cellular and two viral proteins. Anti-influenza activity for 48 of them has been reported previously, whereas the antiviral efficacy of the 665 remains unknown. Studying anti-influenza efficacy and immuno/neuro-modulating properties of these compounds and their combinations as well as potential viral and host resistance to them may lead to the discovery of novel modulators of IAV–host interactions, which might be more effective than the currently available anti-influenza therapeutics.

The Chemistry and Biological Activities of Mimosine: A Review

Mimosine [β-[N-(3-hydroxy-4-oxypyridyl)]-α-aminopropionic acid] is a non-protein amino acid found in the members of Mimosoideae family. There are a considerable number of reports available on the chemistry, methods for estimation, biosynthesis, regulation, and degradation of this secondary metabolite. On the other hand, over the past years of active research, mimosine has been found to have various biological activities such as anti-cancer, antiinflammation, anti-fibrosis, anti-influenza, anti-virus, herbicidal and insecticidal activities, and others. Mimosine is a leading compound of interest for use in the development of RAC/CDC42-activated kinase 1 (PAK1)-specific inhibitors for the treatment of various diseases/disorders, because PAK1 is not essential for the growth of normal cells. Interestingly, the new roles of mimosine in malignant glioma treatment, regenerative dentistry, and phytoremediation are being emerged. These identified properties indicate an exciting future for this amino acid. The present review is focused on the chemistry and recognized biological activities of mimosine in an attempt to draw a link between these two characteristics. Copyright © 2016 John Wiley & Sons, Ltd.

Artepillin C and Other Herbal PAK1-blockers: Effects on Hair Cell Proliferation and Related PAK1-dependent Biological Function in Cell Culture

PAK1 (RAC/CDC42-activated kinase 1) is the major oncogenic kinase, and a number of herbal PAK1-blockers such as propolis and curcumin have been shown to be anti-oncogenic and anti-melanogenic as well as anti-alopecia (promoting hair growth). Previously, we found several distinct PAK1-inhibitors in Okinawa plants including Alpinia zerumbet (alpinia). Thus, here, we tested the effects of these herbal compounds and their derivatives on the growth of cancer or normal hair cells, and melanogenesis in cell culture of A549 lung cancer, hair follicle dermal papilla cell, and B16F10 melanoma. Among these herbal PAK1-inhibitors, cucurbitacin I from bitter melon (Goya) turned out to be the most potent to inhibit the growth of human lung cancer cells with the IC50 around 140 nM and to promote the growth of hair cells with the effective dose around 10 nM. Hispidin, a metabolite of 5,6-dehydrokawain from alpinia, inhibited the growth of cancer cells with the IC50 of 25 μM as does artepillin C, the major anti-cancer ingredient in Brazilian green propolis. Mimosine tetrapeptides (MFWY, MFYY, and MFFY) and hispidin derivatives (H1-3) also exhibited a strong anti-cancer activity with the IC50 ranging from 16 to 30 μM. Mimosine tetrapeptides and hispidin derivatives strongly suppressed the melanogenesis in melanoma cells.

Mimosine Dipeptide Enantiomsers: Improved Inhibitors against Melanogenesis and Cyclooxygenase

Melanogenesis plays an important role in the protection of skin against UV through production of melanin pigments, but abnormal accumulation of this pigment causes unaesthetic hyperpigmentation. Much effort is being made to develop effective depigmenting agents. Here, we show for the first time that a small library of mimosine dipeptide enantiomers (Mi-l/d-amino acid) inhibit the melanogenesis in B16F10 melanoma cells by down-regulating the cellular tyrosinase with little effect on their growth or viability. Two of them, Mi-d-Trp and Mi-d-Val, turned out to be the most potent inhibitors on melanin content and cellular tyrosinase in B16F10 melanoma cells. In addition, most of the mimosine dipeptides were more potent than mimosine for inhibiting cyclooxygenase 1 (COX-1) with IC₅₀ of 18–26 μM. Among them, Mi-l-Val and Mi-l-Trp inhibited cyclooxygenase 2 (COX-2) more potently than indomethacin, with IC₅₀ values of 22 and 19 μM, respectively. Taken together, our results suggest the possibility that mimosine dipeptides could be better candidates (than mimosine) for anti-melanogenic (skin hyperpigmentation treatment) and cyclooxygenase (COX) inhibition.

Discovery of Potent Cysteine-Containing Dipeptide Inhibitors against Tyrosinase: A Comprehensive Investigation of 20 × 20 Dipeptides in Inhibiting Dopachrome Formation

Tyrosinase is an essential copper-containing enzyme required for melanin synthesis. The overproduction and abnormal accumulation of melanin cause hyperpigmentation and neurodegenerative diseases. Thus, tyrosinase is promising for use in medicine and cosmetics. Our previous study identified a natural product, A5, resembling the structure of the dipeptide WY and apparently inhibiting tyrosinase. Here, we comprehensively estimated the inhibitory capability of 20 × 20 dipeptides against mushroom tyrosinase. We found that cysteine-containing dipeptides, directly blocking the active site of tyrosinase, are highly potent in inhibition; in particular, N-terminal cysteine-containing dipeptides markedly outperform the C-terminal-containing ones. The cysteine-containing dipeptides, CE, CS, CY, and CW, show comparative bioactivities, and tyrosine-containing dipeptides are substrate-like inhibitors. The dipeptide PD attenuates 16.5% melanin content without any significant cytotoxicity. This study reveals the functional role of cysteine residue positional preference and the selectivity of specific amino acids in cysteine-containing dipeptides against tyrosinase, aiding in developing skin-whitening products.

Phage display-mediated discovery of novel tyrosinase-targeting tetrapeptide inhibitors reveals the significance of N-terminal preference of cysteine residues and their functional sulfur atom

Tyrosinase, a key copper-containing enzyme involved in melanin biosynthesis, is closely associated with hyperpigmentation disorders, cancer, and neurodegenerative diseases, and as such, it is an essential target in medicine and cosmetics. Known tyrosinase inhibitors possess adverse side effects, and there are no safety regulations; therefore, it is necessary to develop new inhibitors with fewer side effects and less toxicity. Peptides are exquisitely specific to their in vivo targets, with high potencies and relatively few off-target side effects. Thus, we systematically and comprehensively investigated the tyrosinase-inhibitory abilities of N- and C-terminal cysteine/tyrosine-containing tetrapeptides by constructing a phage-display random tetrapeptide library and conducting computational molecular docking studies on novel tyrosinase tetrapeptide inhibitors. We found that N-terminal cysteine-containing tetrapeptides exhibited the most potent tyrosinase-inhibitory abilities. The positional preference of cysteine residues at the N terminus in the tetrapeptides significantly contributed to their tyrosinase-inhibitory function. The sulfur atom in cysteine moieties of N- and C-terminal cysteine-containing tetrapeptides coordinated with copper ions, which then tightly blocked substrate-binding sites. N- and C-terminal tyrosine-containing tetrapeptides functioned as competitive inhibitors against mushroom tyrosinase by using the phenol ring of tyrosine to stack with the imidazole ring of His263, thus competing for the substrate-binding site. The N-terminal cysteine-containing tetrapeptide CRVI exhibited the strongest tyrosinase-inhibitory potency (with an IC50 of 2.7 ± 0.5 μM), which was superior to those of the known tyrosinase inhibitors (arbutin and kojic acid) and outperformed kojic acid-tripeptides, mimosine-FFY, and short-sequence oligopeptides at inhibiting mushroom tyrosinase.