Amino groups s. a. Amines

FIGURE 5.6 Reaction of ninhydrin (trioxohydrindene hydrate) with the amino group of a bound residue (A) generates the Schiff s base. Hydrolysis after shift of the double bond generates the aldehyde and another amine which reacts (B) with a second molecule of ninhydrin to give an equilibrium mixture of the anion depicted and its tetraoxo form with a maximum of absorbance at 570 nm. 

Hydroxyl resins have been converted to chloroformates or active carbonates to provide solid supports that can be used for reversible anchoring of amines as carbamates. Thus, nitrophenylcarbonate 2a (Table 2) has been used to anchor symmetrical diamines and, after further reactions, treatment with TFA released products as trifluoroacetamides [104]. A chloroformate derivative of Tentagel-S 2b has been used to anchor the amino group of a-amino acids and the products used to synthesize dipeptides that could be cleaved by TFA [105]. Succinimidylcarbonate resins 2c have been prepared by treatment of... 

The decarboxylative cyclization could be prevented by using two equivalents of the corresponding aldehyde component 395, which led to spirodihydropyridines 396 as shown by Li et al. (Scheme 13.82) [139], or by exchanging the amino group by a hydroxyl substituent and adding ammonium acetate as the amine source [ 159]. In this 4CR, the Meldrum s acid moiety is hydrolyzed to give the carboxyhc acid 399 that is stabilized by an intramolecular hydrogen bond. 

A mixture of caffeine, 2-propanol, dicumyl peroxide, and water irradiated 22 hrs. with the Pyrex-filtered light of a Hanovia 450 w. high-pressure Hg-vapor lamp -> product. Y 92%. F. e., also with other photoinitiators, s. J. Salomon and D. Elad, J. Org. Chem. 38, 3420 (1973) 39, 1470 (1974) with amines, with and without elimination of the amino group, s. Photochem. Photobiol. 19, 21 (1974). 

Sodium Bisulfite. Sodium bisulfite [7631-90-5] NaHSO, is occasionally used to perform simultaneous reduction of a nitro group to an amine and the addition of a sulfonic acid group. For example, 4-amino-3-hydroxyl-l-naphthalenesulfonic acid [116-63-2] C qH NO S, is manufactured from 2-naphthol in a process which uses sodium bisulfite (59). The process involves nitrosation of 2-naphthol in aqueous medium, followed by addition of sodium bisulfite and acidification with sulfuric acid. 

Pyridoxal Derivatives. Various aldehydes of pyridoxal (Table 3) react with hemoglobin at sites that can be somewhat controlled by the state of oxygenation (36,59). It is thereby possible to achieve derivatives having a wide range of functional properties. The reaction, shown for PLP in Figure 3, involves first the formation of a Schiff s base between the amino groups of hemoglobin and the aldehyde(s) of the pyridoxal compound, followed by reduction of the Schiff s base with sodium borohydride, to yield a covalendy-linked pyridoxyl derivative in the form of a secondary amine. 

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