Ester amide exchange

Rolgamidine (14) is a dihydropyrrole derivative which has antidiarrheal activity It can be synthesized by alkylation of trans 2,5-dimethyl-3 pyrroline (12) with methyl bromoacefate to give 13 An amide-ester exchange reaction with guanidine hydrochloride completes the synthesis of rolgamidine (14) [3]... 

Another interesting convertible isocyanide, 2-(t-butyldimethylsilyloxymethyl)-phenyl isocyanide 21 was used by Linderman and co-workers [10] in a reaction with formic acid, benzylamine, and benzaldehyde to afford the Ugi adduct 22, which, upon acid treatment followed by basification, underwent O-desilylation and amide/ester exchange to afford the ester 23 (Scheme 2.8). A remarkable feature of 21 is the high diastereoselectivity observed when it is employed in combination with chiral aminosugar derivatives in Ugi-4CR [10]. 

Table 5.8. Graft copolymer formation in binary PA/PO blends by amide-ester exchange...

PA-Styrene Copolymer Formation by Amide-ester Exchange... 

In detail, the 3 -hydroxy-group of the ribose (in the terminal adenosine residue of each tRNA molecule) is acylated, enzymatically, by an activated form of that amino acid for which this tRNA is specific. Amide-ester exchange of these esters with peptidyl-tRNA on the ribosomes then occurs under the direction of mRNAs. In the latter step, the growing peptide is transferred from the tRNA bond on the donor site of the ribosomes to an aminoacyl-tRNA bond on the acceptor site of the same ribosome. This reaction is catalysed by the enzyme peptidyl transferase. The peptide, lengthened in this way, is then entirely shifted to the donor site with the help of a translocation enzyme. The next aminoacyl-tRNA then becomes bound to the vacant acceptor site, and the process is repeated. The terminal groups of the tRNAs are always —XCCA, where C is a cytidylic, and A an adenylic, acid residue. 

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