| HS Code | 554403 |
| Product Name | DL-Homocysteine Thiolactone Hydrochloride |
| Cas Number | 6038-19-3 |
| Molecular Formula | C4H8ClNOS |
| Molecular Weight | 153.63 g/mol |
| Appearance | White crystalline powder |
| Solubility | Soluble in water, dimethyl sulfoxide, and ethanol |
| Melting Point | 190-193 °C (decomposes) |
| Storage Conditions | Store at -20 °C, protected from moisture and light |
| Purity | ≥98% |
| Synonym | DL-2-Amino-4-mercaptobutyric acid gamma-thiolactone hydrochloride |
As an accredited DL-Homocysteine Thiolactone Salt factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | 25 g of DL-Homocysteine Thiolactone Salt in a sealed amber glass bottle, stored dry and protected from light. |
| Container Loading (20′ FCL) | One 20-foot FCL container securely stows DL-Homocysteine Thiolactone Salt, ensuring safe, stable loading with proper packaging and ventilation. |
| Shipping | DL-Homocysteine Thiolactone Salt ships as a moisture-sensitive solid in sealed, inert packaging under ambient temperature. Ensure desiccant presence, protect from light, and label as non-hazardous for laboratory use. Avoid extreme heat or humidity during transit to maintain stability and purity. |
| Storage | Store DL-Homocysteine Thiolactone Salt tightly sealed in a cool, dry place, ideally at -20°C. Protect from light and moisture; store under inert gas if possible. Keep away from oxidizing agents and acids. Use desiccant within the container to prevent hydrolysis and maintain stability. |
| Shelf Life | Shelf life: store at -20°C, desiccated, and protected from light; stable for at least 12 months under these conditions. |
Clinical diagnostic manufacturing lines that require lot-to-lot consistent total homocysteine calibrators and controls for LC-MS/MS or other non-stereospecific detection platforms can use DL-homocysteine thiolactone salt as a storage-stable precursor for free homocysteine generation. The solid salt is dissolved in nitrogen-purged water at 4 °C to a stock concentration between 10 mmol/L and 100 mmol/L, then mixed with carbonate/bicarbonate buffer to pH 8.5 ± 0.2 and incubated at 37 °C for 15–30 min. Thiolactone ring opening proceeds with a 1:1 molar conversion to homocysteine, and residual thiolactone is monitored by HPLC-UV at 205 nm with an acceptance limit of ≤0.5 area%. Working calibrator dilutions are prepared gravimetrically at ratios from 1:100 to 1:2000 into delipidated human serum containing 0.1 g/L sodium azide and 0.5 g/L EDTA; disulfide reduction is maintained with tris(2-carboxyethyl)phosphine at 0.5–1.0 mmol/L. The filling and lyophilization line operates under ISO 13485:2016 and IVDR 2017/746, while metrological traceability follows ISO 17511:2020 and method comparison uses CLSI EP09c. The racemic nature of the DL-salt is acceptable only where the detection principle does not distinguish enantiomers; for L-selective enzymatic homocysteine assays, the L-enantiomer standard must be used. Terminal product formats include liquid ready-to-use calibrator kits, lyophilized three-level control sets, and external quality assessment panels for plasma total homocysteine measurement.
In the manufacture of citiolone, N-acetylhomocysteine thiolactone, DL-homocysteine thiolactone salt is charged as the primary thiolactone scaffold. A representative production protocol dissolves the salt in water at 1.0–1.5 mol/L, adds sodium acetate buffer, and feeds acetic anhydride at 1.05–1.20 mol per mol thiolactone salt while maintaining pH 6.5–7.5 with sodium hydroxide and a jacket setpoint of 0–10 °C. The reaction is held for 60–90 min, quenched with dilute hydrochloric acid to pH 2.0, extracted with ethyl acetate, and crystallized from ethanol/water at 50:50 v/v; vacuum drying at 40 °C for 8 h yields a white crystalline intermediate. Production hardware for a 500 L glass-lined reactor includes a retreat-blade agitator at 120–150 rpm and jacket circulation capable of maintaining ±2 °C at setpoint during exothermic acetylation. Drug-substance chemical development is governed by ICH Q7 Chapter 12 for process validation, ICH Q3C for residual solvent control, ICH Q3D for elemental impurity risk assessment, and ICH Q11 for impurity fate mapping. Terminal product types include citiolone tablets, oral granules, and powder sachets where the thiolactone moiety remains the pharmacophore.
| Quality Attribute | Analytical Method | Acceptance Limit |
|---|---|---|
| Assay on anhydrous basis | HPLC-UV, USP 621 | 98.0–102.0% |
| Related substances | HPLC-UV | single impurity ≤ 0.10%, total ≤ 0.50% |
| Residual acetic acid | GC-HS, USP 467 | ≤ 5000 ppm |
| Elemental impurities | ICP-MS, ICH Q3D | Class 1 metals per monograph |
Thiolation of lysine ε-amino groups in carrier proteins, monoclonal antibodies, and diagnostic enzymes proceeds through ring-opening aminolysis of DL-homocysteine thiolactone salt, generating a pendant homocysteinamide with a free terminal sulfhydryl for subsequent maleimide or iodoacetyl conjugation. In a standard bioconjugation batch, the salt is solubilized in degassed phosphate-buffered saline at pH 7.2–7.4 and added to the protein solution at 10–50 mol per mol accessible lysine, with final protein concentration held at 5–10 mg/mL and reaction time 2–4 h at 22 °C under nitrogen. Thiolation degree is quantified by Ellman’s reagent at 412 nm and generally falls between 3 and 15 sulfhydryl groups per protein molecule depending on solvent-accessible lysine content. Excess reagent and low-molecular-weight reaction products are removed by size-exclusion chromatography using a Sephadex G-25 column equilibrated with 20 mmol/L Tris-HCl, 150 mmol/L sodium chloride, and 1 mmol/L EDTA at pH 7.0. Compliance for clinical conjugation intermediates references ICH Q5A viral safety, ICH Q5D cell substrate qualification, and USP <1043> ancillary material risk assessment; for diagnostic conjugate lots, ISO 13485:2016 batch records apply. Sterile filtration through a 0.22 µm PVDF membrane is performed before formulation. Terminal product types include thiolated IgG intermediates for maleimide-linked enzyme–antibody conjugates, thiolated collagen and gelatin carriers for drug delivery, and surface-immobilized capture ligands used in lateral flow detection systems.
Preclinical studies of hyperhomocysteinemia-associated endothelial dysfunction use DL-homocysteine thiolactone salt to elevate intracellular and extracellular protein N-homocysteinylation in a controlled manner. In primary human umbilical vein endothelial cell cultures, the salt is added to supplemented endothelial growth medium at final concentrations from 50 µmol/L to 500 µmol/L for 2–24 h; because thiolactone hydrolysis at pH 7.4 and 37 °C proceeds rapidly, dosing solutions are prepared within 30 min of use or replaced at 4 h intervals during extended exposure protocols. The resulting protein damage is monitored by western blot using anti-N-homocysteinylated protein antibodies and by LC-MS/MS detection of homocysteine-lysine adducts. For animal studies, published data for this specific configuration is limited; dose rates for osmotic minipump administration have been reported in terms of thiolactone delivered per kg body weight but require species-specific validation because circulating thiolactone is hydrolyzed by serum lactonases. Nonclinical laboratory studies intended for regulatory submission follow OECD GLP principles and ARRIVE 2.0 reporting guidelines; animal care protocols reference the NIH Guide for the Care and Use of Laboratory Animals. Terminal products are not commercial end goods but include endothelial dysfunction model systems, protein modification biomarkers, and antibody reagents used to detect N-homocysteinylated albumin in cardiovascular research cohorts.
Fine chemical synthesis of S-adenosylhomocysteine analogs and biotinylated homocysteine probes begins with alkaline ring opening of DL-homocysteine thiolactone salt to generate a free thiolate. In a preparative route, the salt is dissolved in 1.0 mol/L sodium hydroxide at 0–5 °C, stirred for 20–30 min, and adjusted to pH 8.5; the thiolate is then treated with a 5′-chloro- or 5′-tosyladenosine derivative at a feed ratio of 1.2 mol thiolate per 1.0 mol electrophile under nitrogen. The S-alkylation is held at 40 °C for 16–24 h and monitored by TLC or HPLC until the adenosine derivative is below 1.0 area%. Work-up includes precipitation from cold ethanol, recrystallization, and vacuum drying at 35 °C. Because the DL-salt produces a diastereomeric mixture when condensed with chiral adenosine derivatives, the product is either chromatographically resolved or specified as a reference mixture. Compliance for research-grade and pharmaceutical raw material supply is documented under ISO 9001:2015 and REACH registration dossiers; where the product enters an active pharmaceutical ingredient route, ICH Q11 starting material designation and USP <621> chromatographic method qualification apply. Terminal products include S-adenosylhomocysteine reference standards, methyltransferase inhibition assay cofactors, and biotinylated homocysteine probes for protein methylation research.
Modification of amine-bearing polysaccharides, including chitosan and amino-functionalized dextran, with DL-homocysteine thiolactone salt introduces pendant sulfhydryl groups for in situ disulfide crosslinking without requiring carbodiimide coupling agents. In a typical process, chitosan is dissolved at 1.0 wt% in 1.0 vol% acetic acid, the pH is raised to 5.0–5.5 with sodium hydroxide, and the salt is added at 20–50 mol% relative to free glucosamine units; the reaction proceeds for 24 h at 25 °C under nitrogen. Batch viscosity increases as thiolation progresses, requiring an anchor impeller at 150 rpm and periodic nitrogen sparging to prevent premature disulfide formation. The degree of thiolation is determined by Ellman’s assay and typically reaches 80–120 µmol thiol per gram of lyophilized polymer when the feed ratio exceeds 40 mol%. Purification by dialysis against dilute acetic acid and then water removes unreacted lactone and inorganic salts. Biomedical device material qualification includes ISO 10993-5 cytotoxicity, ISO 10993-23 irritation testing, and ISO 10993-18 chemical characterization for leachables. Terminal product types comprise thiolated chitosan hydrogels for mucoadhesive wound dressings, disulfide-crosslinked films, and drug-loaded nanoparticles prepared by ionic gelation with sodium tripolyphosphate at 0.1 wt%.
Competitive DL-Homocysteine Thiolactone Salt prices that fit your budget—flexible terms and customized quotes for every order.
For samples, pricing, or more information, please contact us at +8615365186327 or mail to admin@ascent-chem.com.
We will respond to you as soon as possible.
Tel: +8615365186327
Email: admin@ascent-chem.com
Flexible payment, competitive price, premium service - Inquire now!
Commercial product offered under the name DL-homocysteine thiolactone salt is routinely supplied as DL-homocysteine thiolactone hydrochloride, CAS 6038-19-3, with molecular formula C₄H₈ClNOS and formula weight 153.63 g/mol. The hydrochloride is a white to off-white crystalline powder with a melting range of 198–202 °C and a solubility of 50 mg/mL in water. The material is a racemic mixture of the two enantiomeric thiolactone forms, and the hydrochloride counterion converts the otherwise low-melting free base into a free-flowing crystalline solid suitable for gravimetric dispensing. The five-membered thiolactone ring masks the sulfur as a cyclic thioester, which avoids the rapid air oxidation observed with free homocysteine and provides a controlled-release thiol for synthetic and biochemical applications.
For specification-driven procurement, the CAS-registered hydrochloride is the reference model. Custom salt forms, including sulfate and nitrate variants, are listed in some supplier catalogs, but published release data for those alternative counterions are limited. The hydrochloride form is preferred where water solubility, defined melting point, and low residue after ashing are required. Stock containers should be stored at 2–8 °C in tightly closed, desiccated conditions. Material exposed to relative humidity above 60% should be vacuum-dried at 40 °C until loss on drying returns to ≤0.50%, because surface water accelerates hydrolysis of the thiolactone ring in subsequent non-aqueous reactions.
DL-Homocysteine as the free amino acid has a terminal sulfhydryl with a thiol pKₐ near 10.4 and is susceptible to metal-catalyzed air oxidation to homocystine at neutral pH. The hydrochloride salt eliminates this oxidation mode because the sulfur is present as a cyclic thioester, not as a free sulfhydryl. The structural difference redirects reactivity toward nucleophilic attack at the thiolactone carbonyl. Primary amines, including lysine ε-amino groups, open the ring to give N-homocysteinyl amide products that retain a free thiol. The free amino acid, by contrast, participates directly in disulfide exchange and Michael addition but requires oxygen exclusion and often a reducing agent such as tris(2-carboxyethyl)phosphine to maintain the reduced state.
In aqueous solution, thiolactone hydrolysis is strongly pH-dependent. Below pH 6.0 the ring is comparatively stable; at pH 7.4 and 37 °C hydrolysis becomes measurable; above pH 9.0 hydroxide-mediated ring opening accelerates rapidly. Therefore, intact-thiolactone processing is not recommended in aqueous buffers above pH 8.5, whereas forced hydrolysis to generate free homocysteine is carried out in 1.0 M sodium hydroxide under nitrogen at 40 °C for 30 min. The resulting thiol solution is used immediately because its oxidation half-life under air is short. Published data for this specific configuration is limited; some studies report reproducible N-homocysteinylation at pH 7.4 with 2–24 h incubation, but quantitative kinetic constants vary with buffer composition and trace-metal contamination.
Release testing on commercial lots is typically performed against a consolidated specification that combines identity, purity, residue, and solubility controls. The values below represent a common research-grade specification; buyers should verify lot-specific certificates of analysis against site quality systems.
| Parameter | Specification | Typical Test Method |
|---|---|---|
| Appearance | White to off-white crystalline powder | Visual inspection |
| Identification | FTIR matches reference spectrum | ATR-FTIR |
| Assay | ≥98.0% | HPLC, UV 210 nm |
| Melting range | 198–202 °C | Capillary melting point |
| Loss on drying | ≤0.50% | Vacuum drying at 60 °C |
| Residue on ignition | ≤0.10% | Gravimetric after 600 °C |
| Heavy metals as Pb | ≤10 ppm | ICP-OES |
| Iron | ≤10 ppm | ICP-OES |
| Solubility | Clear to faint yellow solution at 50 mg/mL in water | Visual/turbidity |
The assay may be determined by reversed-phase HPLC with UV detection at 210 nm or by non-aqueous titration of the chloride salt. Melting range is determined by capillary methods in accordance with national pharmacopoeial monographs. Elemental impurity limits are aligned with ICH Q3D when the material is ordered for pharmaceutical-support work; general research-grade material is tested for heavy metals by ICP-OES. The residue-on-ignition limit is particularly relevant when the thiolactone is used as a monomer precursor in electronic or biomedical polymer synthesis, where non-volatile inorganic contaminants of ≤10 ppm are often specified.
In protein-modification studies, the hydrochloride is dissolved in phosphate-buffered saline at pH 7.4 to form a concentrated stock, typically 10–100 mM, and then diluted into the reaction mixture to a final concentration of 0.1–10 mM. Incubation at 37 °C for 2–24 h produces N-homocysteinyl lysine adducts by nucleophilic attack of lysine ε-amino groups on the thiolactone carbonyl. The modification density is controlled by pH, temperature, and reaction time rather than by the amount of free thiol in solution. Primary amine buffers such as Tris are avoided because they consume the thiolactone and reduce target modification efficiency. Product formation is detected by anti-N-homocysteinyl protein antibodies or by mass-spectrometric detection of a discrete mass shift on lysine-containing peptides. In cell-culture exposure, the thiolactone is filtered through a 0.22 µm membrane and used at 1–100 µM in serum-supplemented medium; the cyclic thioester is taken up by cells and reacts intracellularly with protein lysine residues. Published data for this specific configuration is limited to research use and should not be extrapolated to in vivo models without further validation. Stock solutions in water are stable for a few hours at room temperature and should be frozen at −20 °C for no more than one working week because repeated freeze-thaw cycles promote hydrolysis.
DL-Homocysteine thiolactone hydrochloride is a racemic mixture, whereas L-homocysteine thiolactone hydrochloride is the enantiopure form used in biochemical and medicinal synthesis where stereochemical fidelity is required. In achiral ring-opening reactions—such as aminolysis with primary amines, hydrolysis to homocysteine, or thiol–ene coupling—the racemate and L-form are functionally equivalent. In enzymatic transformations or chiral resolution processes, the D-enantiomer in the DL product can be inert or inhibitory, and the material should be replaced with the L-form or subjected to chiral preparative chromatography. For medicinal chemistry, the α-amino group of the thiolactone can be acylated or coupled to carboxylate-bearing substrates before ring opening, providing a route to S-substituted homocysteine derivatives without exposing a free thiol to oxidation during intermediate purification. The thiolactone carbonyl is activated toward aminolysis, so couplings involving primary amines are carried out below 0 °C in anhydrous solvents to control the ring-opening rate; typical solvent systems include dichloromethane or tetrahydrofuran with 1.0–1.2 molar equivalents of tertiary amine.
| Form | Identifier | Key Advantage | Operational Boundary |
|---|---|---|---|
| DL-Homocysteine thiolactone hydrochloride | CAS 6038-19-3 | Lower cost, racemic masked thiol | Not for stereospecific enzymatic synthesis |
| L-Homocysteine thiolactone hydrochloride | CAS 31828-68-9 | Natural stereochemistry | Higher cost; limited supplier inventory |
| DL-Homocysteine free amino acid | CAS 454-29-5 | Immediate free thiol | Oxidizes to homocystine at neutral pH |
| N-Acetylhomocysteine thiolactone | N-protected derivative | Selective thiol release after deprotection | Requires an additional deprotection step |
The choice between these forms is determined by downstream coupling chemistry. If the α-amino group must remain free for peptide coupling, the unprotected DL-homocysteine thiolactone salt is appropriate. If the sulfur must remain masked until a later step, the N-acetyl derivative may be preferred because the acetyl group blocks the α-amine and permits selective thiolactone ring-opening at a defined stage. The free amino acid is selected only when an immediate free sulfhydryl is required and oxygen can be excluded.
In thiol–ene polymer formulations, the hydrochloride is first neutralized with 1.0 molar equivalent of a non-nucleophilic tertiary amine, such as triethylamine, to liberate the free thiolactone. The resulting monomer is soluble in common acrylate monomers and can be incorporated into oligomers without premature gelation because the thiolactone ring does not participate in radical propagation until an amine is added. Subsequent aminolysis with a multifunctional primary amine opens the ring and generates a thiol in situ; the thiol then participates in radical thiol–ene coupling under 365 nm UV irradiation using 1.0 mol% 2,2-dimethoxy-2-phenylacetophenone. This sequence eliminates the need to store and meter free thiols, which is a significant operational advantage in continuous photopolymerization lines. In thiol–epoxy systems, the liberated thiol is used as a latent curing agent; the pot life of the mixed formulation is extended because the thiol is not present in active form until the ring-opening trigger is added.
Field-scale handling records indicate that neutralization should be performed under dry nitrogen and with cooling because the hydrochloride releases heat on contact with liquid tertiary amines. Batch-to-batch variance in bulk powder particle size can influence the neutralization rate in stirred reactors; sieving through a 500 µm screen before charging reduces localized clumping and ensures reproducible conversion.
The free α-amino group in DL-homocysteine thiolactone hydrochloride can participate in amide bond formation, but the thiolactone ring is not compatible with strongly basic coupling conditions that deprotonate the α-amine and simultaneously expose the carbonyl to hydroxide. Standard carbodiimide-mediated couplings in dimethylformamide require careful pH control; without pre-neutralization, the hydrochloride reduces the effective basicity of tertiary amine catalysts. In addition, the racemic center at the α-carbon means that peptide chains incorporating this monomer are diastereomeric mixtures unless chiral resolution is performed before coupling. This is a defined operational boundary, not a formulation defect. Published data for this specific configuration is limited; most peptide laboratories therefore use the L-enantiomer for sequence-defined peptides and reserve the DL salt for non-sequence-specific polymer modification.
For solid-phase synthesis, pre-activation with 1-hydroxybenzotriazole and diisopropylcarbodiimide in dichloromethane at 0 °C is used to anchor the thiolactone monomer to a resin-bound carboxylate. The protected thiolactone is stable under these conditions for 4–6 h. Longer coupling times are avoided because trace moisture promotes ring opening to homocysteine, which then oxidizes to homocystine and generates chain termination.
Compared with S-adenosylhomocysteine and S-methylhomocysteine, the thiolactone salt has a free carboxyl-derived carbonyl in the ring, making it reactive toward amines. S-Methylhomocysteine and S-adenosylhomocysteine are already thioethers and do not undergo the same ring-opening thiol release. This difference is exploited when a controlled thiol release is required but free sulfhydryl compounds are unsuitable because of odor, oxidation, or premature reaction. The cyclic thioester also has lower odor than free homocysteine and methanethiol-generating derivatives, which is an advantage in production-scale handling.
In anhydrous dimethylformamide, the hydrochloride is sparingly soluble until neutralized. After neutralization with triethylamine, the free thiolactone is soluble enough for homogeneous coupling at 0.1–0.5 M. The resulting solution should be used within 8 h at 0–5 °C, because slow lactone hydrolysis by residual water in the solvent produces homocysteine and reduces active titer. Solvent water content should be confirmed by Karl Fischer titration before use; a water level below 0.05% w/w is recommended for moisture-sensitive oligomerizations.
Aqueous processing of DL-homocysteine thiolactone hydrochloride is bounded by two competing requirements: sufficient water to dissolve the salt and sufficiently low pH to keep the thiolactone ring intact. The hydrochloride dissolves readily in water, but solutions at neutral to alkaline pH undergo time-dependent hydrolysis to homocysteine. For reagent preparation, chilled buffers at pH 6.0–7.0 are preferred if the intact thiolactone is to be retained. For complete hydrolysis to homocysteine, the salt is dissolved in 1.0 M sodium hydroxide under nitrogen and held at 40 °C for 30 min; this procedure is used for calibration standards and for preparing homocysteine derivatives in situ.
Incompatibilities include strong oxidizing agents such as peroxides, hypochlorite, and permanganate, which oxidize the sulfur after ring opening. Strong primary or secondary amines should not be stored with the salt because exothermic aminolysis may occur; this is especially relevant in bulk blending operations where local temperature rise can exceed 5 °C if amine addition is not controlled. The product is not classified as flammable, but thermal decomposition products include sulfur oxides, hydrogen chloride, and nitrogen oxides under fire conditions. Empty containers retain product residues and should not be cut, welded, or heated without decontamination.
As an analytical reference material, the hydrochloride salt is used to prepare homocysteine calibration solutions after controlled alkaline hydrolysis. The hydrolysis product is derivatized with a thiol-specific fluorescent label and separated by HPLC with fluorescence detection. This application requires the DL form because the assay method does not distinguish enantiomers, and the racemate is acceptable for total homocysteine quantification. The salt is weighed into 0.1 M hydrochloric acid to prevent oxidation before derivatization.
Incoming lots should be checked for appearance, loss on drying, and FTIR identity. If these three parameters meet the specification, the material is accepted for synthesis; if any parameter deviates, the lot is reallocated to hydrolysis-only use where the thiolactone ring is intentionally opened and the resulting homocysteine is consumed immediately.
