3-(Methylseleno)-L-alanine
[CAS# 26046-90-2]

Identification

• Classification: Biochemical >> Amino acids and their derivatives >> Alanine derivatives
• Name: 3-(Methylseleno)-L-alanine
• Synonyms: Se-Methyl-seleno-L-cysteine; (R)-2-Amino-3-methylselanyl propionic acid
• Molecular Formula: C₄H₉NO₂Se
• Molecular Weight: 182.08
• Protein Sequence: X
• CAS Registry Number: 26046-90-2
• EC Number: 684-218-7
• SMILES: C[Se]C[C@@H](C(=O)O)N

Properties

• Boiling point: 314.1±37.0 °C 760 mmHg (Calc.)^*
• Flash point: 143.7±26.5 °C (Calc.)^*

^* Calculated using Advanced Chemistry Development (ACD/Labs) Software.

Safety Data

• Hazard Symbols: GHS06;GHS08;GHS09 Danger
• Risk Statements: H301-H331-H373-H400-H410
• Safety Statements: P260-P261-P264-P270-P271-P273-P301+P316-P304+P340-P316-P319-P321-P330-P391-P403+P233-P405-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Specific target organ toxicity - repeated exposure	STOT RE	2	H373
Acute toxicity	Acute Tox.	3	H331
Acute toxicity	Acute Tox.	3	H301
Chronic hazardous to the aquatic environment	Aquatic Chronic	1	H410
Acute hazardous to the aquatic environment	Aquatic Acute	1	H400

• Transport Information: UN 3283

Discovery and Applications

3-(Methylseleno)-L-alanine is more commonly known as Se-methylselenocysteine, with CAS number 26046-90-2. It is a seleno-amino acid in which the selenium atom replaces sulfur in the side chain and is methylated. Its formula is C₄H₉NO₂Se, and it belongs to the class of alpha amino acids.

This compound occurs naturally in plants of the Allium and Brassica families (such as garlic, broccoli, and onions), where it is synthesized via selenium metabolism pathways. It is produced enzymatically through methylation of selenocysteine by plant selenocysteine methyltransferases. In these organisms, Se-methylselenocysteine accumulates as a nonproteinogenic selenium form, which avoids misincorporation into proteins yet serves as a selenium reservoir or detoxification product.

In biomedical and nutritional research, Se-methylselenocysteine has gained interest for its chemopreventive and antioxidant properties. Studies have shown that it may protect against certain cancers in animal models, acting through formation of methylselenol, induction of apoptosis in transformed cells, modulation of redox status, and enhancement of antioxidant enzyme expression. Because it does not readily integrate into proteins, it has lower toxicity than some other selenium compounds.

Analytically, Se-methylselenocysteine is used as a standard in selenium speciation assays including XANES and chromatographic techniques. Its presence in biological extracts is used to distinguish organic selenium pools in food, plants, and tissues. Its metabolic fate has been studied in mammals, where it is metabolized via β-lyase activity to methylselenol and further to hydrogen selenide, contributing to the endogenous selenium pool used in selenoprotein synthesis and redox signaling.

Because it is not a primary metabolite of central pathways, Se-methylselenocysteine’s “discovery” is diffuse: it was characterized in biochemical studies of selenium in plants and later in nutrition research. Its increasing use in studies of selenium homeostasis and cancer chemoprevention reflects its utility as a relatively safe and functional selenium donor.

References

Wehrle RJ, SteMarie EJ, Hondal RJ, Masterson DS (2019) Synthesis of α-methylselenocysteine and its utilization as a glutathione peroxidase mimic. Journal of Peptide Science, 25(6).
DOI: [https://doi.org/10.1002/psc.3173](https://doi.org/10.1002/psc.3173)

Amoako PO, Uden PC, Tyson JF (2009) Speciation of selenium dietary supplements; formation of S-(methylseleno)cysteine and other selenium compounds. Analytica Chimica Acta, 652(1–2).
DOI: [https://doi.org/10.1016/j.aca.2009.08.013](https://doi.org/10.1016/j.aca.2009.08.013)

Rahmanto AS, Davies MJ (2012) Selenium-containing amino acids as direct and indirect antioxidants. IUBMB Life, 64(11).
DOI: [https://doi.org/10.1002/iub.1084](https://doi.org/10.1002/iub.1084)