Tert-butoxycarbonyl amide

The individual amino acid building blocks are first incubated with di-tert-butyl dicarbonate, thus forming a tert-butoxycarbonyl amide (BOC) amino acid derivative. 

Keywords tert-butoxycarbonyl amide, microwave irradiation, amine, ester... 

The enantiomeric excess of the product is determined by Mosher amide formation and NMR analysis as follows (R)-(N-tert-butoxycarbonyl)allylglycine is dissolved in 3 mL of IM ethanolic HCl and heated to reflux for 2 hr. The reaction is cooled and the solvent removed under vacuum. The crude amino ester hydrochloride is dissolved in 0.3 mL of pyridine and 0.3 mL of CCI4. To this mixture is added 25 mg (0.10 mmol) of (+)-a-methoxy-a-(trifluoromethyl)phenylacetyl chloride and the reaction is stirred for 6 hr at room temperature. The reaction is quenched with 1 mL water, taken up in diethyl ether, and washed consecutively with IM HCl, saturated aqueous NaHC03, and water. The ether layer is dried over anhydrous MgS04, filtered and evaporated. The Mosher amide formation is repeated with ( )-a-methoxy-a-(trifluoromethyl)phenylacetyl chloride, and, now with this reference standard, the two products are compared by H NMR. 

Peptide synthesis is made possible by the use of selective protecting groups. An N-protected amino acid with a free carboxyl group is coupled to an 0-protected amino acid with a free amino group in the presence of dicyclo-hexylcarbodiimide (DCC). Amide formation occurs, the protecting groups are removed, and the sequence is repeated. Amines are usually protected as their tert-butoxycarbonyl (BOO derivatives, and acids are protected as esters. This synthetic sequence is often carried out by the Merrifield solid-phase technique, in which the peptide is esterified to an insoluble polymeric support. 

Keywords A-tert-butoxycarbonyl group, Yb(OTf)3, silica gel, amide... 

Fu et al. revealed that Cul/L-proline-catalyzed intramolecular cyclization of amides 136 could proceed smoothly to afford medium- and large-sized nitrogen heterocycles 137 (Scheme 49) [87], The introduction of a phosphoryl or tert-butoxycarbonyl group at iV-termini was found essential for this macrocyclization. 

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