Amino acid N-carboxyanhydrides, also called Leuchs' anhydrides, are a family of heterocyclic organic compounds derived from amino acids. They are white, moisture-reactive solids. They have been evaluated for applications the field of biomaterials.
Preparation
NCAs are typically prepared by phosgenation of amino acids:
They were first synthesized by Hermann Leuchs by heating an N-ethoxycarbonyl or N-methoxycarbonyl amino acid chloride in a vacuum at 50-70 °C:
A moisture-tolerant route to unprotected NCAs employs epoxides as scavengers of hydrogen chloride. This synthesis of NCAs is sometimes called the Leuchs method. The relatively high temperatures necessary for this cyclization results in the decomposition of several NCAs. Of several improvements, one notable procedure involves treating an unprotected amino acid with phosgene or its trimer.
Reactions NCAs are prone to hydrolysis to the parent amino acid:
RCHNHC(O)OC(O) + H2O → H2NCH(R)CO2H + CO2 Some derivatives however tolerate water briefly. NCAs convert to homopolypeptides ( [N(H)CH(R)CO)]n) through ring-opening polymerization:
n RCHNHC(O)OC(O) → [N(H)CH(R)CO)]n + n CO2 Poly-L-lysine has been prepared from N-carbobenzyloxy-α-N-carboxy-L-lysine anhydride, followed by deprotection with phosphonium iodide. Peptide synthesis from NCAs does not require protection of the amino acid functional groups. N-Substituted NCAs, such as sulfenamide derivatives have also been examined. The ring-opening polymerization of NCAs is catalyzed by metal catalysts. The polymerization of NCA’s have been considered as a prebiotic route to polypeptides. NCAs can also be used to form amides and lactams by reaction of carboxylic acids and isocyanates.
See also Dakin–West reaction Glycine N-carboxyanhydride, the parent NCA
References
Further reading Barrett SE, Burke RS, Abrams MT, Bason C, Busuek M, Carlini E, et al. (June 2014). "Development of a liver-targeted siRNA delivery platform with a broad therapeutic window utilizing biodegradable polypeptide-based polymer conjugates". Journal of Controlled Release. 183: 124–37. doi:10.1016/j.jconrel.2014.03.028. PMID 24657948. Grazon C, Salas-Ambrosio P, Ibarboure E, Buol A, Garanger E, Grinstaff MW, et al. (January 2020). "Aqueous Ring-Opening Polymerization-Induced Self-Assembly (ROPISA) of N-Carboxyanhydrides" (PDF). Angewandte Chemie. 59 (2): 622–626. doi:10.1002/ange.201912028. PMID 31650664. S2CID 241302007. Jiang, Jinhui; Zhang, Xinyue; Fan, Zhen; Du, Jianzhong (2019-10-15). "Ring-Opening Polymerization of N-Carboxyanhydride-Induced Self-Assembly for Fabricating Biodegradable Polymer Vesicles". ACS Macro Letters. 8 (10): 1216–1221. doi:10.1021/acsmacrolett.9b00606. PMID 35651173. S2CID 203135939. Kramer JR, Onoa B, Bustamante C, Bertozzi CR (October 2015). "Chemically tunable mucin chimeras assembled on living cells". Proceedings of the National Academy of Sciences of the United States of America. 112 (41): 12574–9. Bibcode:2015PNAS..11212574K. doi:10.1073/pnas.1516127112. PMC 4611660. PMID 26420872.