Cysteine Derivatives Research Articles

Poecillastrosides, Steroidal Saponins from the Mediterranean Deep-Sea Sponge Poecillastra compressa (Bowerbank, 1866).

The first chemical investigation of the Mediterranean deep-sea sponge Poecillastra compressa (Bowerbank, 1866) led to the identification of seven new steroidal saponins named poecillastrosides A–G (1–7). All saponins feature an oxidized methyl at C-18 into a primary alcohol or a carboxylic acid. While poecillastrosides A–D (1–4) all contain an exo double bond at C-24 of the side-chain and two osidic residues connected at O-2′, poecillastrosides E–G (5–7) are characterized by a cyclopropane on the side-chain and a connection at O-3′ between both sugar units. The chemical structures were elucidated through extensive spectroscopic analysis (High-Resolution Mass Spectrometry (HRESIMS), 1D and 2D NMR) and the absolute configurations of the sugar residues were assigned after acidic hydrolysis and cysteine derivatization followed by LC-HRMS analyses. Poecillastrosides D and E, bearing a carboxylic acid at C-18, were shown to exhibit antifungal activity against Aspergillus fumigatus.

Visible-light photoredox-catalyzed desulfurization of thiol- and disulfide-containing amino acids and small peptides.

A scalable protocol for the desulfurization of cysteine by using visible light, the photocatalyst Ir(dF(CF3 )ppy)2 (dtb-bpy)PF6 and triethylphosphite under biphasic reaction conditions has been developed. The loading of the catalyst can be as low as 0.01mol%, which can be efficiently removed during the workup (≤0.3ppm), giving rise to the corresponding desulfurized product in high yields. This method has been applied also to cystine, penicillamine, and reduced and oxidized glutathione. The desulfurization has been found to be pH sensitive, with an optimal pH value of 6.5 and 7.0 for the cysteine derivatives and glutathione, respectively. In addition, during the desulfurization of a decapeptide containing cysteine and methionine, concurrent oxidation of the two sulfur-containing residues to disulfide and sulfoxide has been observed. Therefore, whereas the presented protocol allows a straightforward visible light-mediated desulfurization of simple thiols by using very low catalyst loading and a cost-effective trialkylphosphite as thiyl radical trapping agent, its application to complex substrates needs to be carefully validated. Copyright © 2017 European Peptide Society and John Wiley & Sons, Ltd.

Impact of S-sulfocysteine on fragments and trisulfide bond linkages in monoclonal antibodies

ABSTRACTThe quality of recombinant proteins such as monoclonal antibodies produced using Chinese hamster ovary cell-based mammalian systems is dependent on many factors, including cell line, process and cell culture media. Due to these factors, the generated product is heterogeneous and may have chemically-induced modifications or post-translational modifications that affect antibody stability, functionality and, in some cases, patient safety. This study demonstrates that S-sulfocysteine, a cysteine derivative, can increase the antibody specific productivity in different cell lines cultivated with different processes while minimizing trisulfide linkages in generated mAbs, mainly between heavy and light chain. The supplementation of a cell culture feed with S-sulfocysteine also proved to be useful to reduce the percentage of antibody fragments generated from the monoclonal antibody. Overall, this new component used in the upstream process allows a reduction of product heterogeneity.

Click Reaction Based on the Biosynthesis of Firefly Luciferin

Novel click chemistry was developed based on the biosynthetic process of firefly luciferin, which includes an ideal coupling of a cyanothiazole residue with cysteine. Among various biomimetic couplings of nitriles with cysteine derivatives, the approach using 4-cyanopyridine and cysteine methyl ester provided a very rapid and quantitative conversion to the corresponding thiazole without any metal catalyst at room temperature.

Challenges in the evaluation of thiol-reactive inhibitors of human protein disulfide Isomerase

This paper addresses how to evaluate the efficacy of the growing inventory of thiol-reactive inhibitors of mammalian protein disulfide Isomerase (PDI) enzymes under realistic concentrations of potentially competing thiol-containing peptides and proteins. For this purpose, we introduce a variant of the widely-used reductase assay by using a commercially-available cysteine derivative (BODIPY FL L-Cystine; BD-SS) that yields a 55-fold increase in fluorescence (excitation/emission; 490/513nm) on scission of the disulfide bond. This plate reader-compatible method detects human PDI down to 5–10nM, can utilize a range of thiol substrates (including 5µM dithiothreitol, 10µM reduced RNase thiols, and 5mM glutathione; GSH), and can operate from pH 6–9.5 in a variety of buffers. PDI assays often employ low micromolar levels of substrates leading to ambiguities when thiol-directed inhibitors are evaluated. The present work utilizes 5mM GSH for both pre-incubation and assay phases to more realistically reflect the high concentration of thiols that an inhibitor would encounter intracellularly. Extracellular PDI faces a much lower concentration of potentially competing thiols; to assess reductase activity under these conditions, the pre-reduced PDI is treated with inhibitor and then fluorescence increase upon reduction of BD-SS is followed in the absence of additional competing thiols. Both assay modes were tested with four mechanistically diverse PDI inhibitors. Two reversible reagents, 3,4-methylenedioxy-β-nitrostyrene (MNS) and the arsenical APAO, were found to be strong inhibitors of PDI in the absence of competing thiols, but were ineffective in the presence of 5mM GSH. A further examination of the nitrostyrene showed that MNS not only forms facile Michael adducts with GSH, but also with the thiols of unfolded proteins (Kd values of 7 and <0.1µM, respectively) suggesting the existence of multiple potential intracellular targets for this membrane-permeant reagent. The inhibition of PDI by the irreversible alkylating agent, the chloroacetamide 16F16, was found to be only modestly attenuated by 5mM GSH. Finally, the thiol-independent flavonoid inhibitor quercetin-3-O-rutinoside was found to show equal efficacy in reoxidation and turnover assay types. This work provides a framework to evaluate inhibitors that may target the CxxC motifs of PDI and addresses some of the complexities in the interpretation of the behavior of thiol-directed reagents in vivo.

Operationally Convenient and Scalable Asymmetric Synthesis of (2S)‐ and (2R)‐α‐(Methyl)cysteine Derivatives through Alkylation of Chiral Alanine Schiff Base NiII Complexes

This research demonstrates that the methylation of N‐benzyl cysteine Schiff base derived NiII complexes leads to the formation of the corresponding dehydroalanine‐containing products and cannot be used for preparation of the target α‐(methyl)cysteine. In sharp contrast, the alternative strategy that involves thiomethylation of NiII complexes of alanine Schiff bases is a viable and practically attractive approach to afford the desired α‐(methyl)cysteine containing derivatives. This work also reveals a significant, and rather unexpected, difference in the stereochemical performance of proline and 3,5‐dihydro‐4H‐dinaphth[2,1‐c:1′,2′‐e]azepine derived chiral ligands, the former of which shows superior performance in terms of chemical yields and diastereoselectivity of the α‐(methyl)cysteine products formed.

A novel role for methyl cysteinate, a cysteine derivative, in cesium accumulation in Arabidopsis thaliana

Phytoaccumulation is a technique to extract metals from soil utilising ability of plants. Cesium is a valuable metal while radioactive isotopes of cesium can be hazardous. In order to establish a more efficient phytoaccumulation system, small molecules which promote plants to accumulate cesium were investigated. Through chemical library screening, 14 chemicals were isolated as ‘cesium accumulators’ in Arabidopsis thaliana. Of those, methyl cysteinate, a derivative of cysteine, was found to function within the plant to accumulate externally supplemented cesium. Moreover, metabolite profiling demonstrated that cesium treatment increased cysteine levels in Arabidopsis. The cesium accumulation effect was not observed for other cysteine derivatives or amino acids on the cysteine metabolic pathway tested. Our results suggest that methyl cysteinate, potentially metabolised from cysteine, binds with cesium on the surface of the roots or inside plant cells and improve phytoaccumulation.

Synthesis, Antioxidative and Whitening Effects of Novel Cysteine Derivatives

Recently, development of biocompatibility functional cosmetic agents as antioxidant or whitening agent has increased. In this study, synthetic cysteine derivatives (DBLS‐21, ‐24, and ‐33) were developed containing syringic acid and cysteine moieties (l‐cysteine ethyl ester, N‐acetyl cysteine methyl ester, and N‐acetyl cysteine ethyl ester), and their antioxidative and whitening activities were evaluated. The cellular protective effect (τ50) of DBLS‐21 was 51.1 min at 50 μM on 1O2 ‐induced hemolysis of erythrocytes. This activity was slightly higher than that of α‐tocopherol (43.6 min) as a lipophilic antioxidant. In the melanogenesis inhibitory effect, DBLS‐21, ‐24, and ‐33 was 1.6‐, 1.8‐, and 2.5‐fold higher than arbutin, respectively. In particular, DBLS‐21 and ‐33 was 112.8‐ and 6.1‐fold higher than arbutin, respectively (293.4 μM) on tyrosinase inhibition activity (IC50 ). But DBLS‐24 had no tyrosinase inhibitory activity. These results suggest that cysteine derivatives possess potential for use as an antioxidant agent (DBLS‐21) and whitening agents (all derivatives) in cosmetics.

Half-sandwich complexes of iridium and ruthenium containing cysteine-derived ligands.

The dimers [{(ηn-ring)MCl}2(μ-Cl)2] ((ηn-ring)M = (η5-C5Me5)Ir, (η6-p-MeC6H4iPr)Ru) react with the modified cysteines S-benzyl-l-cysteine (HL1) or S-benzyl-α-methyl-l-cysteine (HL2) affording cationic complexes of the formula [(ηn-ring)MCl(κ2N,S-HL)]Cl (1, 2) in good yield. Addition of NaHCO3 to complexes 1 and 2 gave equilibrium mixtures of neutral [(ηn-ring)MCl(κ2N,O-L)] (3, 4) and cationic [(ηn-ring)M(κ3N,O,S-L)]Cl (6Cl, 7Cl) complexes. Similar mixtures were obtained in one-pot reaction by successive addition of the modified cysteine and NaHCO3 to the above formulated dimers. Addition of the N-Boc substituted cysteine derivative S-benzyl-N-Boc-l-cysteine (HL3) and NaHCO3 to the dimers [{(ηn-ring)MCl}2(μ-Cl)2] affords the neutral compounds [(ηn-ring)MCl(κ2O,S-L3)] ((ηn-ring)M = (η5-C5Me5)Ir (5a), (η6-p-MeC6H4iPr)Ru (5b)). Complexes of the formula [(ηn-ring)MCl(κ3N,O,S-L)][SbF6] (6Sb-8Sb), in which the cysteine derivative acts as a tridentate chelate ligand, can be prepared by adding one equivalent of AgSbF6 to the solutions of compounds 5 or to the mixtures of complexes 3/6Cl and 4/7Cl. The amide proton of compounds 8aSb and 8bSb can be removed by addition of NaHCO3 affording the neutral complexes [(ηn-ring)M(κ3N,O,S-L3-H)] ((ηn-ring)M = (η5-C5Me5)Ir (9a), (η6-p-MeC6H4iPr)Ru (9b)). Complexes 9a and 9b can also be prepared by reacting the dimers [{(ηn-ring)MCl}2(μ-Cl)2] with HL3 and two equivalents of NaHCO3. The absolute configuration of the complexes has been established by spectroscopic and diffractometric means including the crystal structure determination of (RIr,RC,RS)-[(η5-C5Me5)Ir(κ3N,O,S-L1)][SbF6] (6aSb). The thermodynamic parameters associated with the epimerization at sulphur that the iridium compound [(η5-C5Me5)Ir(κ3N,O,S-L3-H)] (9a) undergoes have been determined through variable temperature 1H NMR studies.

可食用果蔬保鲜剂CTS-cys的合成

利用壳聚糖(CTS)良好的成膜，抑菌性和L-半胱氨酸(L-cys)良好的抑菌，抗氧化性，通过化学改性法制备了巯基含量高达333 μmol/g的L-cys改性CTS (CTS-cys)。采用抑菌圈法研究了CTS、L-cys和CTS-cys对大肠杆菌、蜡样芽孢杆菌和金黄色葡萄球菌的抑菌效果。实验结果表明：在被测试范围内，L-cys对三种菌株均有很好抑菌性；CTS-cys对大肠杆菌、金黄色葡萄球菌均有较好抑菌效果，最大抑菌率为89%，92.9%，对蜡样芽孢杆菌的最大抑菌率只有60.5%；CTS对三种菌株的最大抑菌率均在50%水平以下，抑菌效果差。壳聚糖半胱氨酸衍生物很大程度上协同了半胱氨酸的抑菌性，大大提高了壳聚糖的抑菌能力。 The L-cys modified CTS (CTS-cys) with the content of thiol up to 333 μmol/g was prepared by chemical modification, which made use of good film formation, bacteriostasis of chitosan (CTS) and good antibacterial, antioxidant of L-cysteine (L-cys). The inhibitory effects of CTS, L-cys and CTS-cys on Escherichia coli, Bacillus cereus and Staphylococcus aureus were studied by the method of inhibition zone. The experimental results as follows: L-cys had good antibacterial activity to the three strains in the tested range; CTS-cys had good antibacterial effect on Escherichia coli and Staphylococcus aureus and the maximum inhibition rate was 89%, 92.9%, while the maximum inhibition rate of CTS-cys against Bacillus cereus was only 60.5%. The maximum inhibition rate of CTS to three strains was lower than 50%, and the inhibitory effect was poor. Chitosan cysteine derivatives have largely coordinated the bacteriostasis of cysteine and greatly enhanced the bacteriostatic ability of chitosan.

Rethinking Cysteine Protective Groups: S-Alkylsulfonyl-l-Cysteines for Chemoselective Disulfide Formation.

The ability to reversibly cross-link proteins and peptides grants the amino acid cysteine its unique role in nature as well as in peptide chemistry. We report a novel class of S-alkylsulfonyl-l-cysteines and N-carboxy anhydrides (NCA) thereof for peptide synthesis. The S-alkylsulfonyl group is stable against amines and thus enables its use under Fmoc chemistry conditions and the controlled polymerization of the corresponding NCAs yielding well-defined homo- as well as block co-polymers. Yet, thiols react immediately with the S-alkylsulfonyl group forming asymmetric disulfides. Therefore, we introduce the first reactive cysteine derivative for efficient and chemoselective disulfide formation in synthetic polypeptides, thus bypassing additional protective group cleavage steps.

In situ complexation of rhodium(II) tetracarboxylates with some derivatives of cysteine and related ligands studied by 1H and 13C nuclear magnetic resonance spectroscopy

The complexation of N-phthaloyl, N-formyl, and N,N-dimethyl derivatives of S-methylcysteine methyl ester (both racemic and optically pure) with three dimeric rhodium(II) salts, acetate Rh2AcO4, trifluoroacetate Rh2TFA4, and (R)-(+)-α-methoxy-α-trifluoromethylphenylacetate Rh2Mosh4 was investigated by nuclear magnetic resonance spectroscopy (NMR) at room and lower temperatures. The complexation was carried out in situ, in CDCl3 solution using titration procedure; the results were examined by the analysis of 1H and 13C NMR chemical shift change (Δδ). The complexation of free S-methyl cysteine and hydrochloride salt of its methyl ester was performed in D2O solution. For comparison, complexation of some derivatives of leucine, phenylalanine, and proline was examined.N-phthaloyl and N-formyl derivatives of cysteine formed 1 : 1 and 1 : 2 axial complexes with all dirhodium salts. Rhodium substrates were bonded via sulfur. In one case, the complexation of Rh2TFA4 by both sulfur and N-formyl oxygen was noted. Similar complexation of Rh2TFA4, via CHO group, was found for N-formyl derivatives of leucine, phenylalanine, and proline. For N,N-dimethyl derivative of cysteine, both N and S atoms were involved in bonding. At room temperature, in all cases, ligand exchange was fast on the NMR timescale.

Cryo-EM structure of respiratory complex I reveals a link to mitochondrial sulfur metabolism

Mitochondrial complex I is a 1MDa membrane protein complex with a central role in aerobic energy metabolism. The bioenergetic core functions are executed by 14 central subunits that are conserved from bacteria to man. Despite recent progress in structure determination, our understanding of the function of the ~30 accessory subunits associated with the mitochondrial complex is still limited. We have investigated the structure of complex I from the aerobic yeast Yarrowia lipolytica by cryo-electron microscopy. Our density map at 7.9Å resolution closely matches the 3.6–3.9Å X-ray structure of the Yarrowia lipolytica complex. However, the cryo-EM map indicated an additional subunit on the side of the matrix arm above the membrane surface, pointing away from the membrane arm. The density, which is not present in any previously described complex I structure and occurs in about 20 % of the particles, was identified as the accessory sulfur transferase subunit ST1. The Yarrowia lipolytica complex I preparation is active in generating H2S from the cysteine derivative 3-mercaptopyruvate, catalyzed by ST1. We thus provide evidence for a link between respiratory complex I and mitochondrial sulfur metabolism.

Green biosynthesis of gold nanoparticles by onion peel extract: Synthesis, characterization and biological activities

Nanoparticles of various noble metals have been studied owing to their eminent outstanding physical and chemical properties, viz. controllable size, surface morphology and surface chemistry. Herein, utilization of the food waste material (aqueous extract of dried onion peels (OP)) to synthesize gold nanoparticles (OP-AuNPs) was investigated along with study of its biological potentials. The synthesized OP-AuNPs were characterized by UV–vis spectroscopy, field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray (EDX) analysis, X-ray powder diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR) and differential thermo gravimetric analysis (DT-TGA) analysis. Surface plasmon resonance spectra were obtained at 535 nm with an average particle size of 45.42 nm. The results of FT-IR confirmed the involvement of various water soluble phenolic compounds and cysteine derivatives in the reduction and stabilization of OP-AuNPs. OP-AuNPs displayed strong synergistic antibacterial and anticandidal activity along with antioxidant and strong proteasome inhibitory potential. The results of the present study will facilitate easy green synthesis of gold nanoparticles using food waste materials and their effective applications in biomedical fields as antibacterial dressings, antibacterial and anticandidal drugs, cancer treatments, proteasome inhibitors, cosmetic industries as sunscreen lotion and anti-aging creams, food sector as antibacterial coatings, and pharmaceutical sectors as medicines and drug formulations.

The Cysteine S-Alkylation Reaction as a Synthetic Method to Covalently Modify Peptide Sequences.

Synthetic methodologies to chemically modify peptide molecules have long been investigated for their impact in the field of chemical biology. They allow the introduction of biochemical probes useful for studying protein functions, for manipulating peptides with therapeutic potential, and for structure-activity relationship investigations. The commonly used approach was the derivatization of an amino acid side chain. In this regard, the cysteine, for its unique reactivity, has been widely employed as the substrate for such modifications. Herein, we report on methodologies developed to modify the cysteine thiol group through the S-alkylation reaction. Some procedures perform the alkylation of cysteine derivatives, in order to prepare building blocks to be used during the peptide synthesis, whilst some others selectively modify peptide sequences containing a cysteine residue with a free thiol group, both in solution and in the solid phase.

Computational survey of ligand properties on iron(III)–iron(II) redox potential: exploring natural attenuation of nitroaromatic compounds

This study is a computational investigation of the ligand effect on the redox potential of iron redox couple aimed at screening these systems for novel applications. The influence of common and naturally available organic compounds with diverse ligand characteristics (nature of donor site, chelation, pre-organization, degree of back acceptance) on the redox potential of iron(III)–iron(II) redox couple has been theoretically calculated using an appropriate level of density functional theory (DFT). The DFT calculated redox potentials of iron complexes are explored to supplement, corroborate, and predict the experimental behavior of the studied systems towards environmental reduction of nitroaromatic compounds to corresponding anilines. The comparative avidity of iron complexes with cysteine derivatives for the reduction of nitroaromatic compounds has been theoretically explored and based on structure–activity relationship; new iron complexes with a range of reactivity and enhanced ability towards nitroaromatic reduction have been predicted.

In Vitro Antifungal Activity of Cysteine Derivatives and their Combinations with Antifungal Agents Against Clinically Relevant Scedosporium species

Background: Members of the genus Scedosporium are emerging human pathogens, causing a wide range of infections. Their treatment means a challenge for clinicians, mostly because of the low susceptibility of these causative agents to conventional antifungal drugs. New alternative therapeutic approaches are required for better clinical outcomes. Cysteine and its derivatives alone or in combinations with antifungal drugs might have improved antifungal effects against Scedosporium species. Methods: The in vitro antifungal effects of two cysteine forms and three of their derivatives (i.e., D-cysteine, L-cysteine, L-cysteine-methyl ester hydrochloride, N-isobutyryl-D-cysteine, and N-isobutyryl-L-cysteine) were determined using the CLSI M38-A2 broth microdilution method. The in vitro drug interactions between the most effective cysteine derivatives and some conventional antifungal drugs were also investigated using checkerboard assays in case of four clinical isolates. Results: L-cysteine-methyl ester hydrochloride proved to be the most effective among the investigated compounds. N-isobutyryl-L-cysteine exhibited antifungal activity against one Scedosporium aurantiacum strain only. D-cysteine, L-cysteine and N-isobutyryl-D-cysteine proved to be ineffective against Scedosporium spp. in the investigated concentration range. No significant differences were found in the susceptibilities between environmental and clinical isolates. L-cysteine-methyl ester hydrochloride could interact synergistically with amphotericin B, caspofungin, terbinafine and voriconazole. Antagonistic interactions were not observed between the investigated compounds. Conclusions: The present study provides an evidence for the in vitro antifungal activity of L-cysteinemethyl ester hydrochloride and the synergistic interactions between this cysteine derivative and conventional antifungal agents. Based on our results, L-cysteine-methyl ester hydrochloride in combination with antifungal drugs could be applicable in the treatment of human Scedosporium infections in the future. However, further studies are required to clarify the antifungal mechanism of L-cysteine-methyl ester hydrochloride and to investigate its activity in vivo.

Efficacy of decontamination foam on a non-polar hazardous chemical surrogate

The release of hazardous chemicals poses a threat to individuals in the area of a release and to responders who attempt to limit the damage of the release. For a liquid phase spill, the most common decontamination technology is a sodium hypochlorite and water solution. Although this solution has been proven effective against a variety of contaminants, it also has a host of drawbacks. Novel decontamination technologies have been developed for military applications, however, they have not been explored with the same depth in the industrial sector. Therefore, there is a need for an industrial decontamination technology that is noncorrosive, nontoxic, nonflammable, and environmentally safe. Decontamination solutions and foams have the potential to improve hazardous chemical spill cleanup, saving time, money, and lives. This work uses a derivative of cysteine, called N-(tert-Butoxycarbonyl)-L-cysteine methyl ester (TCME), as a surrogate for non-polar hazardous industrial bio-chemicals. Previous work has been done to compare the effect of decontamination foam against other decontamination solutions, however in the work the contaminants were typically polar, thus easily able to dissolve in the foam and react rapidly. In this work, the effect of less polar contaminants is studied, introducing transport limitations as well as reaction limitations. Additionally, this work examines the effect of surfactant on decontamination reactions by using water based decontamination solution and decontamination foam as decon technologies. All experiments were conducted in the liquid phase and results were analyzed using GC-MS to determine the extent of reaction.

High-performance thin-layer chromatography and pressurized planar electrochromatography of some diastereomeric amino acid derivatives in reversed-phase system with carboxylic acid mobile phase buffers

The separation of 1-fluoro-2,4-dinitrophenyl-5-l-valine amide (FVDA) diastereomeric derivatives of aspartic acid, cysteine, and histidine by means of high-performance thin-layer chromatography (HPTLC) as well as pressurized planar electrochromatography (PPEC) techniques in systems with HPTLC RP-18W plates and the various acetonitrile—buffer mobile phases is presented. The influence of the mobile phase components, i.e., acetonitrile concentration and buffer kind on migration distance of the solute zones, was investigated. The effect of mono (formic) and various dicarboxylic acids (oxalic, malonic, maleic, malic, succinic, tartaric, and pimelic) as the mobile phase buffer components on the solute retention was studied. It is observed that an increase of acetonitrile content of the mobile phase affects the solute zone migration and retention in PPEC and HPTLC. What is more, the separation selectivity in the latter and former techniques differs. The PPEC mode presents a higher efficiency in comparison with HP...

Synthesis, Characterization, and Evaluation of Thiazolidine Derivatives of Cysteine for Suppressing Eumelanin Production.

In the pathway of melanin biosynthesis, cysteine (Cys) is utilized for the synthesis of pheomelanin. Accordingly, Cys is considered to suppress the formation of brown-black eumelanin. Although attempts have been made to utilize Cys and its derivatives as skin-whitening agents, their instability and odor hinders their application as a cosmetic agent. Herein, N-acetyl-2-methylthiazolidine-2,4-dicarboxylic acid ethyl ester (AcCP2Et) was proposed as a candidate for a stable and prolonged-release derivative of Cys to inhibit dopachrome formation after its degradation in melanocytes. It was synthesized by acetylation of 2-methylthiazolidine-2,4-dicarboxylic acid 2-ethyl ester (CP2Et), the condensation derivative of Cys and ethyl pyruvate. AcCP2Et suppressed melanogenesis in melanocytes in vitro, was stable in phosphate buffer at 70°C for five days, and exhibited far less odor than CP2Et. Therefore, AcCP2Et was validated to be a useful deriative of Cys for application as a skin-whitening agent. AcCP2Et comprises four stereoisomers; thus characterization of each stereoisomer was required. The stereochemistry of AcCP2Et was confirmed via a single-crystal X-ray structure analysis of N-acetyl-2-methylthiazolidine-2,4-dicarboxylic acid (AcCP) derived from AcCP2Et. In the synthesis of AcCP2Et, the acetylation of CP2Et proceeded with epimerization at C4 to give trans-isomers when excess acetyl chloride and an organic amine was used, whereas it proceeded while retaining the original (R) configuration at C4 to give the cis- and trans-isomer when an equivalent of acetyl chloride with an inorganic base was used. These results indicate that the formation of an intermolecular mixed acid anhydride is responsible for the isomerization at the C4 asymmetric center.