Hydrazides in Synthesis

Despite the ease of formation, the use of hydrazides in carbohydrate synthesis has thus far been limited. Early work often reported the acylation of glycosyl hydrazides 

The high yielding nature of glycosyl hydrazide formation has allowed the late stage introduction of oligosaccharides on scaffolds for multivalent display. The first example of such was a mimic of a mucin produced by Godula and Bertozzi 

Given the success of Bertozzi s example, it is perhaps surprising that not more multivalent scaffolds based on glycosyl hydrazide chemistry have been reported. One of the few examples has been described by Liu and coworkers, who have shown that oligosaccharides can readily be displayed on modified poly(amido amine) (PAMAM) dendrimers via a hydrazide linkage. These dendrimers were shown to be readily taken up by hepatocytes in a glycan-dependent fashion [35]. Similarly, dendrimers have been used to increase the density of carbohydrate 

Lectin-Labeling Strategies Using Clycosyl Hydrazides 

The approach works remarkably well as it is site selective, reacting with amino acids in close proximity to the carbohydrate-binding site, as well as protein selective working well in a mixture of proteins. Unfortunately, the hydrazide used in this 

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Next, the hydrazides 41a-e were used in synthesis of different 1,2,3-triazole-3-thiones and l,3,4-oxadiazole-2-thiones. Thus, treatment of 41 e with phenyl isothiocyanate in boiling temperature for 4 h gave the thiosemi-carbazide solid, which separated and boiled directly with 5% NaOH for 3 h to provide, after neutralization with dilute HCl, 55 (67%). Similarly, treatment of 41d with 4-methoxyphenylisocyanate afforded 51 (62%). 

Allylation of acyloyl-imidazoles and pyrazoles61 with allyl halide mediated by indium in aqueous media provides a facile regioselective synthesis of P, y-unsaturated ketones (Scheme 11.1), which has been applied to the synthesis of the monoterpene artemesia ketone. The same product can be obtained by indium-mediated allylation of acyl cyanide (Eq. 11.35).62 Samarium, gallium, and bismuth can be used as a mediator for the allylation of nitrones and hydrazones to give homoallylic hydroxylamine and hydrazides in aqueous media in the presence of Bu4NBr (Scheme 11.2).63 The reaction with gallium and bismuth can be increased dramatically under microwave activation. 

This method has been employed for the synthesis of aluminum hydrazides in only few, but quite interesting cases. The reaction of azobenzene with an arylaluminum dihydride [aryl = tri(tert-butyl)phenyl] was reported to afford a... 

More recently Peng and Song reported the rapid synthesis of a library of hydrazides in a MW-US combined reactor (Scheme 9.20)139. Unlike the aforementioned system that employed decalin as an energy transfer medium for the ultrasound irradiation, in their modified domestic oven, the horn was immersed directly into the reaction mixture. 

The synthesis of the first silylhydrazines was described in the 1950s51,52. In spite of the successful use of lithium hydrazides in preparative chemistry, the first structure analyses were carried out over 30 years later53,54. Nowadays dimeric, trimeric, tetrameric and hexameric hydrazides have been described53-58. 

An expedient synthesis of 3,5-disubstituted-l,2,4-triazoles proceeding by the direct reaction of a nitrile and a hydrazide in presence of catalyst K2CO3 in n-BuOH has been developed by Yeung et al. [22], A diverse range of functionality and heterocycles were tolerated under the reaction conditions. A quick preparation of symmetrically 3,5-disubstituted-4-amino-1,2,4-triazoles, under microwave condition is also reported by Bentiss et al. [23]. 

Zhao et al. [32] applied the microwaves for the synthesis of diverse 3,5,6-trisubstituted-l,2,4-triazines (xx) in excellent yields and purity. The synthetic protocol involved the reaction of benzyl and imidazoyl acyl hydrazide in presence of ammonium acetate and glacial HO Ac. 

An efficient one-pot, three-component synthesis of substituted 1,2,4-triazoles 164 has been reported from primary amines 161, dimethylamino acetals 162, and acyl hydrazides 163 <04OL2969>. 1,3-Benzoxazine 165 reacted with acyl hydrazides in refluxing methanol to give... 

Useful preparative procedures have been given for the conversion of phosphonic and phosphinic chlorides to amides and hydrazides. The reverse reaction also may be useful in synthesis and is best carried out by treating the appropriate amide with hydrogen chloride in an inert solvent. This latter reaction not unexpectedly proceeds with retention of configuration on (85), whereas the acyclic analogues undergo racemization. ... 

This technique has also been used to add a cyano group to an aromatic ring. l-Methoxy-4-methoxycarbonyl pyridinium methyl sulphate was absorbed on silica gel particles. After these particles had been dried under vacuum, they were placed in a column and H CN was passed through the column. Then the column was sealed and heated at 40 °C for 5 minutes. After the methyl-2[ C]cyano-isonicotinate had been purified by HPLC chromatography, it was converted into 2-[ C]-isonicotinic acid hydrazide in a 30% radiochemical yield by treatment with hydrazine in anhydrous ethanol (equation 78). The synthesis took 30 minutes to complete. 

The triazine ring system is a component of commercial dyes, herbicides, insecticides, and even pharmaceutical compounds. By application of microwave technology, a general procedure has been developed for rapid synthesis of diverse 3,5,6-trisubstituted 1,2,4-triazines from a variety of 1,2-diketones and acyl hydrazides in excellent yields and purities (Scheme 10.52) [107]. 

Utilities of some carbon nucleophiles in heterocyclic s5mthesis 07C(X1853. Utility of cyanoacetic acid hydrazide in heterocychc synthesis 06ARK(9)... 

First, examples of fluorescence [235] and chemiluminescence-based biosensors [236], derived fix)m PTs, were reported by Tripathy and coworkers. Later, the synthesis of 119 containing pendant biotin units was described. A water-soluble copolymer 120 with sulfonate and biotin in the side chains [237] exhibits a deep violet color (Amax = 550 run) which turns yellow (A ax = 400 nm) on binding with avidin. An extension of this work based on the homopolymer 121 involved the preparation of monolayers of a biotinylated PT on an aminosilane-treated ITO surface by successive deposition of 121 and biocytin hydrazide in electrostatic interactions [238,239]. This ultrathin film modified electrode was shown to detect femtomoles of avidin in aqueous solution. Electrochemical and optical evidences for avidin binding were reported for a copolymer based on poly(terthiophene) 122 [240] and for the homopolymer 123 [198]. 

The Gewald synthesis of 2-aminothiophen-3-carboxylic acid derivatives has been extended to cyanoacetic acid hydrazides. In the base-catalysed reaction with cyclohexanone and sulphur, the hydrazides yielded the thienopyrimidone derivative (24), which could be hydrolysed to the 2-aminothiophen-3-carboxylic acid hydrazide (24a). A series of substituted 2-aminothiophen-3-carboxylic esters have been prepared by a... 

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