Carboxy group migration

The full paper has appeared on the solvolysis of the dibenzyl ester (28) of phosphoenolpyruvic acid and on the related phosphonate ester (29). Reversible phosphoryl migration from the enol oxygen to the carboxy-group occurs readily in (28) and (29) but only to a small extent - and probably not reversibly-in the monoanion (30) and phosphoenolpyruvic acid itself. These observations are readily accounted for in terms of the expected ease of pseudorotation between the various configurations of the... 

The tropane alkaloids commonly occur as esters of tropic acid [as 6.67) and tiglic acid [as 6.75) The former acid arises preferentially from phenylalanine possibly via cinnamic acid and the entire carbon skeleton is involved. The results of C-labelling studies show that, in the rearrangement which occurs during biosynthesis, it is the carboxy group which migrates (see Scheme 6.18). Proof of an... 

With respect to the olefinic substrate, various functional groups are tolerated, e.g. ester, ether, carboxy or cyano groups. Primary and secondary allylic alcohols, e.g. 14, react with concomitant migration of the double bond, to give an enol derivative, which then tautomerizes to the corresponding aldehyde (e.g. 15) or ketone ... 

FIGURE 8.7 Synthesis of a protected tripeptide containing a 2-hydroxy-4-methoxybenzyl-protected peptide bond.38 (A) Acylation of the carboxy-terminal residue, (B) removal of both protecting groups, (C) O-acylation of the benzyl-protector by the symmetrical anhydride of the amino-terminal residue, and (D) migration of the protected amino-terminal residue from the oxygen atom to the amino group of the dipeptide ester. 

An interesting and mechanistically unsettled problem of organocobalt chemistry is the 1,2-shift of a /1-carboxy or -hydroxy group in the homolytic Co—C bond fission-recombination process. The evidence for cobalt participation in the rearrangement is substantial, but its role is not yet clarified (Scheme 103). The heterolytic process also appears to be viable in the migration of a /1-hydroxy or -alkoxy group. 

The results showed that these peptides could be separated from each other at different pH values. It is obvious that these peptides exhibit different charge and a small change in the pH of the buffer, particularly near the pKas of the amino terminal or carboxy terminal or side groups. Since all of the investigated peptides contained the same amino acids, the amino acid sequence can influence the pKas of the ionizable side groups and thus influence the migration behavior of the peptides. 

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