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Chemical name: N-alpha-(9-Fluorenylmethyloxycarbonyl)-L-aspartic acid cyanosulfurylide // Synonyms: (S,Z)-4-((((9H-fluoren-9-yl)methoxy)carbonyl)amino)-4-carboxy-1-cyano-1-(dimethylsulfonio)but-1-en-2-olate, Fmoc-Asp(CSY)-OH
|Molecular weight:||438,50 g/mol|
Aspartimide formation by cyclization of the aspartic acid residue during peptide synthesis results in lowered yields and increased accumulation of side products, thus requiring time-consuming and costly purifications. The utilization of the new protecting group cyanosulfurylide (CSY) to mask carboxylic acids by a stable C-C bond allows to address this drawback and avoid aspartimide formation. CSYs are stable towards strong acids, strong bases, transition metals, and strong reducing agents.
Deprotection is recommended in solution after global deprotection. Peptides are dissolved in acetic aqueous buffer (e.g. NaOAc, pH 4.5, 200 mM) or acidic saline (e.g. pH 3.0, 400mM NaCl). If required for peptide solubility, up to 35% CH3CN can be added. Treatment with NCS results in quantitative conversion to the free acid. Deprotection can be monitored by HPLC and/or LC-MS as CSYs are strongly absorbing at 254 nm.
Note: NCS is not compatible with methionine, which however can be substituted with norleucine in SPPS.
Furthermore, the hydrophilic character of the ylide improves overall peptide solubility and thus efficiency.
Prevention of aspartimide formation during peptide synthesis using cyanosulfurylides as carboxylic acid-protecting groups; K. Neumann, J. Farnung, S. Baldauf, J. W. Bode; Nat. Commun. 2020; 11 (982). https://doi.org/10.1038/s41467-020-14755-6.
Cyanosulfurylides (CSY): carboxylic acid protecting groups that prevent aspartimide formation during peptide synthesis; K. Neumann, J. Farnung, S. Baldauf, J. W. Bode; ChemRxiv 2019; 1-23. https://doi.org/10.26434/chemrxiv.9767027.
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