Amino acid tetraalkylammonium salt

In a rather nontraditional approach to acid protection, the tetraalkylammonium salts of amino acids allow for coupling of HOBt-activated amino acids in yields of 55-84%. ... 

W-Alkylidene derivatives of glycine esters are the preferred starting compounds for the synthesis of unnatural amino acids via the deprotonation/alkylation procedure. Enolate formation is achieved with a strong base (LDA, BuLi, or phosphazene bases such as 2- tert-butylimino)-2-(ethylamino)-l,3-dimethyl-l,3,2-diazaphosphinane) or by phase-transfer catalysis (tetraalkylammonium salts with NaOH or the latter method allows... 

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