Searching for Interesting Non-Canonical Amino Acids
Figure 1: Synthesis of D‑Luciferin.
The 1,2‑aminothiol group of D‑cysteine and the 6‑hydroxybenzothiazole‑2‑carbonitrile undergo the condensation reaction under physiological conditions to build D‑luciferin (Liang et al., 2010).
Figure 2: The condensation reaction of CL and a CBT‑derivative.
The 1,2‑aminothiol group of the side chain of CL and the cyano group of the CBT‑derivative undergo the same condensation reaction under physiological conditions like D‑cysteine and 6‑hydroxybenzothiazole‑2‑carbonitrile.
Designing a Novel Amino Acid
Figure 3: Structure of ACBT.
The amino group at the benzene ring can be used for the coupling reaction and the cyano group at the thiazole ring enables the condensation reaction.
Synthesizing a Novel Amino Acid
Figure 4: Schematic synthesis of ACBT with Cl‑NBT as the educt.
First, the chlorine atom of the Cl‑NBT is substituted with a cyano group (i) to give 6‑nitrobenzothiazole‑2‑carbonitrile (NBT‑CN). The second step is the reduction of the nitro group of NBT‑CN to an amino group (ii) resulting in ACBT.
Figure 5: Schematic coupling reaction of ACBT and N‑Fmoc‑aspartic acid‑OAllyl ester.
Due to the protecting groups, only the carboxy group of N‑Fmoc‑aspartic acid‑OAllyl ester can react with the amino group of ACBT. Using isobutyl chloroformate and 4‑methylmorpholine enables the coupling reaction.
Figure 6: Deprotection of N‑Fmoc‑CBT‑asparagine‑OAllyl ester.
By adding 3x the equivalent of morpholine to the protected N‑Fmoc‑CBT‑asparagine‑OAllyl ester, we could directly remove both protecting groups resulting in the free form of the novel amino acid CBT-asparagine.
Figure 7: Schematic condensation reaction of CL and CBT‑asparagine.
The natural condensation reaction of 1,2‑aminothiols and 6‑hydroxybenzothiazole‑2‑carbonitrile provides a new way to produce fusion proteins and polymer peptides by binding both amino acids.
Modeling New Aminoacyl-tRNA Synthetases by in silico Simulation
Figure 8: CBT-asparagine in the binding site of K2201300.
Liang, G., Ren, H., and Rao, J. (2010). A biocompatible condensation reaction for controlled assembly of nanostructures in living cells. Nat. Chem. 2: 54–60.
Nguyen, D.P., Elliott, T., Holt, M., Muir, T.W., and Chin, J.W. (2011). Genetically Encoded 1,2-Aminothiols Facilitate Rapid and Site-Specific Protein Labeling via a Bio-orthogonal Cyanobenzothiazole Condensation. J. Am. Chem. Soc. 133: 11418–11421.