PubMed · 13304041
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M S FISH, N M JOHNSON, E P LAWRENCE, E C HORNING. 1955. Oxidative N-dealkylation.. https://doi.org/10.1016/0006-3002(55)90150-5
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5-Cyanoimino-4-oxomethylene-4,5-dihydroimidazoles (1) (R at N1) have been discussed as possible intermediates in nitrosative guanine deamination, which are formed by dediazoniation and deprotonation of guaninediazonium ion. The parent system 1 (R = H) and its N1 derivatives 2 (R = Me) and 3 (R = MOM) are considered here. Protonation of 1-3, respectively, may occur either at the cyano-N to form cations 4 (R = H), 6 (R = Me), and 8 (R = MOM) or at the imino-N to form cations 5 (R = H), 7 (R = Me), and 9 (R = MOM), respectively. This protonation is the first step in the acid-catalyzed water addition to form 5-cyanoimino-imidazole-4-carboxylic acid, which then leads to oxanosine. There also exists the option of a substitution reaction by water at the R group of 6-9, and this dealkylation forms N-[4-(oxomethylene)-imidazol-5-yl]carbodiimide (10) and N-[4-(oxomethylene)-imidazol-5-yl]cyanamide (11). In the case of DNA, the R group is a deoxyribose sugar, and attack by water leads to deglycation. To explore this reaction option, the S(N)1 and S(N)2 reactions of 6-9 with water were studied at the MP2/6-31G*//RHF/6-31G* and CCSD/6-31G*//RHF/6-31G* levels, with the inclusion of implicit solvation at the IPCM(MP2/6-31G*)//RHF/6-31G* level, and the electron density distributions of tautomers 1, 10, and 11 were analyzed. The low barriers determined for the MOM transfer show that the deglycation could occur at room temperature but that the process cannot compete with water addition.
The acyl trypsin was prepared by use of an inverse substrate, which is comprise of a photoresponsive 4-phenylazobenzoyl moiety. The acyl group in acyl trypsin has been shown to isomerize from trans-form (4t-trypsin) to cis-form (4c-trypsin)/from cis-form to trans-form by irradiation of UV-vis light. The deacylation rate of the cis-form (4c-trypsin) has been shown to be 18.6 times faster than that of the trans-form (4t-trypsin).
A general method for the synthesis of C-glycosyl amino acids is described here. The stereoisomerically pure tyrosine analogues alpha-L-4 and beta-L-6 are prepared in reasonable overall yields from allyl derivatives 10 and 11. The key step is a benzannulation procedure which is employed in the creation of the aromatic ring that bears the amino acid function.