Isothiocyanates, reaction with amino

It is known, however, that isothiocyanates on their own can form stable self-assembled monolayers on gold (Section V.E), and amine-terminated monolayers were reported to show unusually low reactivity towards electrophilic reagents329,330. It is therefore possible that the observed immobilization of eosin is due not to reaction with amino groups, but to either insertion of the eosin isothiocyanate into a disordered layer of cysteamine, or even replacement of cysteamine monolayer with the molecules of S=C=N—eosin. Because the experimental data on reactions in gold-thiol monolayers are scarce, chemical transformations described in this section should be interpreted with some caution. 

Methyl isothiocyanate also reacts with sulfhydryl groups, but this complication can be turned into an advantage when the reaction is carried out at slightly acidic pH, under which conditions the reaction with amino groups is slow. The S-methylthiocarbamoyl derivatives (75) exhibit a weak uv band —(NH—CH—CO)—... 

Azaindolizine, 5-chloro-nucleophilic substitution, 4, 458 8-Azaindolizine, 7-chloro-nucleophilic substitution, 4, 458 Azaindolizines basicity, 4, 454 electronic spectra, 4, 445 electrophilic substitution, 4, 453 halogenation, 4, 457 hydrogen/deuterium exchange, 4, 458 NMR, 4, 447, 449 nucleophilic attack, 4, 458 protonation, 4, 453 reaction with isothiocyanates, 4, 513 reactions, 5, 267 reviews, 4, 444 UV spectra, 4, 446, 449 Azaindolizines, amino-tautomerism, 4, 452... 

Cycloaddition of 2-nitrosopyridine 48 with nitrile oxides can give either di-A -oxides such as 49 or 3-mono-A -oxides such as 50 (93JHC287). In general, greater electron withdrawing character in the aromatic substituent appears to favor formation of the di-A -oxides. Sulfur ylides such as compound 51 are obtained from aryl isothiocyanates and l-amino-2-methylthiopyridinium iodides (84JCS(P1)1891) nitrogen ylides can be obtained from a similar reaction (86H(24)3363). 

Tible 1 Color reactions of amino acids with fluorescein isothiocyanate — ninhydrin (extract from original table). 

Another main subject of research of Garcia Gonzalez, with the collaboration of J. Femandez-Bolanos, was the reaction of amino sugars with isothiocyanic acid derivatives. 2-Amino-2-deoxy-D-glucose hydrochloride and potassium thiocyanate were shown to give rise to 4-(D-arabino-tetritol-l-... 

Contrasting with the reported formation of fused [l,3,4]thiadiazole rings in the course of the reaction of 3-substituted-4-amino-5-thio-47/-[l,2,4]triazoles 83 with various isothiocyanates (cf. Section 11.07.8.3, Table 3), the reactions with methyl isothiocyanate and with phenylisocyanate afford 3,7-disubstituted-6,7-dihydro-57/-[l,2,4]triazolo[4,3-f] [l,2,4]triazole-6-thiones 110 and -triazole-6-ones 111, respectively (Equation 29) <1986MI607, 1992IJB167>.The same reaction of 4-amino-l-methyl-3,5-bis(methylthio)[l,2,4]triazolium iodide 112 with aryl isothiocyanates yields the mesoionic compounds 113 (Equation 30) <1984TL5427, 1986T2121>. 

Saccharidic templates bearing an amino group in C-2, C-6, C-3, C-5. Generally, an amine located on non-anomeric position reacts similarly through the condensation reaction with carbon disulfide or thiophosgene, the preliminary formed isothiocyanate leads to spontaneous or base-induced cyclization into 1,3-oxazolidine- or l,3-oxazine-2-thiones, as previously mentioned. Several extensive studies are reported about the selective introduction of thionocarbamate moieties on carbohydrate scaffolds.3 22 23 320 34 38... 

In 1950 an alternative to the Sanger procedure for identifying N-terminal amino acids was reported by Edman—reaction with phenyl-isothiocyanate to give a phenylthiocarbamide labeled peptide. When this was heated in anhydrous HC1 in nitromethane, phenylthiohy-dantoin was split off, releasing the free a-NH2 group of the amino acid in position 2 in the sequence. While initially the FDNB method was probably the more popular, the quantitative precision which could be obtained by the Edman degradation has been successfully adapted to the automatic analysis of peptides in sequenators. 

Isatoic anhydride can be used as a versatile synthon for the synthesis of a diverse set of molecules. The isatoic anhydride can be reacted with amines, amides, hydrazides, isothiocyanates, diketo substrates, aminoacids, amino-, thio or hydroxy anilines, as well as in a three-component reaction with aldehydes and amines to form a large set of diverse pharmacophores. 

Isothiocyanates react with many nucleophiles, but only the products with amines (thiocarbamoyl derivatives) are stable.16 Although the increased specificity is desirable, the reaction with the amino group changes the charge on the protein, and this may be needed in order to maintain the activity or the conformation, or both. The linkage formed is alkali-labile, and, as with the azo derivatives, the aromatic ring is a liability. 

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