Glutamine, rearrangement

Scheme 45 Electrochemically induced Hofmann rearrangement of N-Boc glutamine with retention of configuration.

Care would have to be exercised when exposing the pentapeptide to hydroxide ion-mediated deprotection conditions since the base-catalyzed rearrangement of iso-glutamine to glutamate in peptidoglycan-related structures has been observed. 

A recent example has been described by Brown et al. who have studied the KR of p-nitrophenyl esters of the d- and i-N-tert-butoxycarbonyl derivatives of glutamine and phenylalanine with ethanol or methanol promoted by chiral lanthanide complexes, providing enantioselectivities of up to 99% ee [302]. On the other hand, an enantioselective hydrolysis of phenylalanine derivatives was reported in 1986, providing a perfect enantiomer discrimination (s> 1000), as a result of catalysis with a tripeptide [303]. In 2007, Maruoka et al. reported the KR of differently a,a-disubstituted a-siloxy aldehydes based on an asymmetric rearrangement into the corresponding chiral acyloins using axially chiral organoaluminium Lewis acids, which provided selectivity factors of up to 39.5... 

Chorismic acid is transformed to p-hydroxybenzoic acid by loss of the enol-pyruvate side chain. Salicylic acid may be synthesized in bacteria after rearrangement to isochorismic acid by a similar reaction. (Formation of salicylic acid from o-coumaric acid in plants, fungi and animals, cf. D 22.2.5.) The amino groups of anthranilic acid and of p-aminobenzoic acid originate from glutamine. Intermediates in the transformation of chorismis acid to these acids are unknown and probably do not occur in the free state. 

Formation of L-histidine is closely related to purine biosynthesis (D 10.4, Fig. 239). ATP is the actual precursor. It condenses with phosphoribosyl pyrophosphate at position 1 before the purine ring is splitted between the positions 1 and 6. An Amadori rearrangement in the two-prime-ribose unit yields the ribulose derivative l-(5 -phosphoribosyl)-4-carboxamido-5-iV-(N -5 -phospho-ribosyl)-formamidinoimidazole, which reacts with glutamine to D-erythro-imidazole glycerol phosphate (the precursor of histidine) and l-(5 -phospho-ribosyl)-4-carboxamido-5-aminoimidazole, which may be regenerated to ATP (D 10.4). 

Household bleach has been used to carry out the Hofmann rearrangement of 3-nitrobenzamide to 3-nitroaniline, while the Hofmann rearrangement of N(2)-protected glutamine esters of N(2)-protected (25 )-4-[(2,2,2-trifluoroethoxy)carbonylamino]-2-aminobutyric acid esters has been successfully achieved by an electrochemical method using a trifluoroethanol-methyl cyanide solvent system." ... 

---