(S)-2-((9-Fluorenylmethyloxyl)amino)-6-((prop-2-ynyloxy)carbonylamino)hexanoic acid

tRNA can be loaded with the propargyl analogue of free L-lysine by pyrrolysyl-tRNA synthetase enabling the biochemist to introduce site specifically an alkyne group into a protein for further click conjugation. Reference: Nguyen D.P. et al.; J. Am. Chem. Soc. 2009; 131: 8720-8721. Direct charging of tRNACUA with pyrrolysine in vitro and in vivo; Blight Sherry et. al; Nature 2004; 431: 333-335. Propargyloxycarbonyl, commonly abbreviated as Poc or Pryoc, can either be used as alkyne component for standard Click conjugation or in combination with tetrazine linkers in copper-free Diels-Alder type Click reactions. It also has applications as unusual protecting group for amines, hydroxy functions and as esters. All 3 are stable to neat TFA, but can be cleaved at ambient temperature with Co2(CO)8 in TFA:DCM. Deprotection with other transition metals like palladium have also been reported. References: N-alkynyl derivatives of 5-fluorouracil: susceptibility to palladium-mediated dealkylation and toxigenicity in cancer cell culture; Jason T. Weiss, Craig Fraser, Belén Rubio-Ruiz, Samuel H. Myers, Richard Crispin, John C. Dawson, Valerie G. Brunton, E. Elizabeth Patton, Neil O. Carragher and Asier Unciti-Broceta; Frontiers in Chemistry 2014; 2(56): 1-9. doi: 10.3389/fchem.2014.00056. Bioorthogonal Catalysis: A General Method To Evaluate Metal-Catalyzed Reactions in Real Time in Living Systems Using a Cellular Luciferase Reporter System; Hsiao-Tieh Hsu, Brian M. Trantow, Robert M. Waymouth, and Paul A. Wender; Bioconjugate Chem. 2015; DOI: 10.1021/acs.bioconjchem.5b00469. Palladium-triggered deprotection chemistry for protein activation in living cells; Jie Li, Juntao Yu, Jingyi Zhao, Jie Wang, Siqi Zheng, Shixian Lin, Long Chen, Maiyun Yang, Shang Jia, Xiaoyu Zhang & Peng R. Chen; Nature Chemistry 2014; 6: 352-361. doi:10.1038/nchem.1887. Propargyloxycarbonyl and propargyl groups for novel protection of amino, hydroxy, and carboxy functions; Yoshiyuki Fukase, Koichi Fukase, Shoichi Kusumoto; Tetrahedron Letters 1999; 40(6): 1169-1170. doi:10.1016/S0040-4039(98)02555-6.