Biguanides structure

An unexpected formation of a biguanide occurred 754) in the reaction of trans-l-amino-2-hydroxycyclohexane (LI) with cyanogen bromide in the presence of sodium acetate. In addition to the expected trans-2-amino-3a,4,5,6,7,7a-hexahydro-benzoxazole (LII), traces of its trimer having the biguanide structure (LIII) were obtained. 

An examination of the n.m.r. spectra of a number of alkylbigUcinides has recently provided valuable evidence concerning the site of protonation in the biguanide-structure 742a). The measurements suggest a S3nnmetrical structure (11) for the monocation. Its further protonation occurs selectively and reversibly at N-3 to produce the dication (I m). Further protonation in concentrated sulphuric acid involves an attack of the proton on the w-electron system of (I m) at N-1, N-2, N-4 and N-5. The trication has consequently one of several possible prototropic structures, one of which is shown (I o). 

A detailed quantitative study of the acid hydrolysis of biguanides has been carried out (653) using Paludrine and three related compounds (LXXII—LXXV) under carefully controlled conditions the results clearly showed that the rate of hydrolysis decreases with increasing degree of substitution in the biguanide-structure. 

Unlike acylamides, sulphonamides react with biguanides to yield mainly open-chain compounds, but the biguanide structure is cleaved in... 

A carbodiimide-grafted polystyrene resin was reacted with tetramethyl-guanidine to give an interesting biguanide structure (Scheme 13). This was assayed as a catalyst for a transesterification reaction.33 Incidentally, resin-bound guanidines are useful bases for processes involving resin capture.34... 

First crystal structure of a Ag complex. g Square plane of N atoms about Ag. The fairly uniform multiple bonding in the C—N bonds indicates that the highly charged Ag is accommodated by extensive delocalization over the whole biguanide structure... 

Similar to the biguanide structures, Dizman et al. created l,4-diazabicyclo[2.2.2]octane (DABCO)-based stmctures carrying two quaternary ammonium charges with butyl and hexyl alkyl extensions (C12). The monomer was assembled by multiple nucleophilic substitution reactions. Polymers were formed by free radical polymerization in water. These polymers, much like the biguanide acrylate and pyridinium polymers, combined hydrophobidty and cationic charge on the same monomer. One difference is that the cationic charge was also separated from the backbone of the polymer by a long alkyl chain. As with the pyridine polymers, the hexyl alkyl monomers were found to be the most effective biocides. 

Structural Chemistry of the Free Ligands, Biuret, Biguanide... 

The structure of a single example of a chloro-substituted biguanide [Cu(clbg)2]Cl2 2H20 (clbg=2-chlorobiguanide),has been reported [34]. Chlorine substitution leads to a reduction in the number of N-H donors from seven to six. Five are involved in the construction of a 2-D architecture (Fig. 15). Two pairs of N-H donors form R2(4) assemblies with separate chlorine atoms the fifth forms a N-H 0 contact to the water molecule which also uses its O-H donors to link two chloride anions (Fig. 15). The resultant 2-D sheet architecture lies parallel to the (2 -1 1) plane. The sixth forms a N-H -Cl contact to a chloride anion in an adjacent sheet. 

The numerous highly coloured metal complexes obtainable from biguanides and elements of the transition series have posed yet another interesting structural problem. The accumulated evidence suggests that the structures agreeing most satisfactorily with the observations are of type (I o M = divalent metal). This aspect of the subject has been discussed fully by Ray [532). 

A recent X-ray-crystallographic investigation [86) has provided the first accurate structural picture of a biguanide derivative, namely that of the antimalarial Paludrine (l-p-chlorophenyl-5-isopropyibiguanide hydrochloride) (Fig. 1). The biguanide part of the cation consists of two... 

Salts of substituted biguanides with N-acylsulphonamides, of general structure [RS0zN-C0R ] [R NH2C( NH)NH-C( NH)NH2] have been prepared (JSO), as have addition complexes with 2-hydroxy-4,6-dimethylpyrimidine (477). 

Attempts to gain further insight into the more detailed structure of biguanides in general, and of Paludrine in particular, were made by studies of their ultraviolet spectra, including those of simpler molecules, which may be regarded as the component parts of l-aryl-5-alkyl-biguanides (227), but the succes of this approach was at first limited (227). 

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