Pyridinium compounds

Paraquat administered to rats by gavage or intravenously at doses, which were approximately equi-toxic (680/unoles/kg and 65/imoles/kg respectively) induced a dilatation of the rough endoplasmic reticulum of the brush cells in the rat s lung (Sykes et al. 1977). 

---

The reduction (136) of pyridinium compounds to 1,2- or 1,4-dihydro products with complex metal hydrides or dithionite leads to cyclic di-enamines of synthetic and biochemical interest. 

Combination of the hydroxyl ion with the mesomeric cation involves the removal of a double bond. For the quaternary pyridinium compounds this causes the total loss of the aromaticity. For quaternary quinolinium and isoquinolinium compounds, the aromatic character of one of the two rings is lost, and for the quaternary acridinium compounds that of one out of three. Hence., the order of stabilities of these compounds (determined by Hantzsch ) is explained. - Comparison of quaternary 3,4-dihydroisoquinolinium compounds and their isoquinolinium analogs with respect to the equilibrium (5) (4) shows that a much higher hydroxyl ion concentration is necessary for the isoquinolinium ions to form the carbinolamine. This is because the transition from the quaternary 3,4-dihydroisoquinolinium ions into the undissociated carbinolamine involves significantly smaller loss of mesomeric energy than that for the quaternary isoquinolinium hydroxides. ... 

A proposed explanation of the reactivity of the 4-position versus that of the 2-position in pyridinium compounds has been advanced by Kosower and Klinedinst nucleophiles which are expected to form charge-transfer complexes will tend to substitute at the 4-position. However, it is not clear why this (usually unknown) property should govern the site of substitution, except for a bifunctional nucleophile such as hydrosulfite ion which can form a suitable bridge from the nitrogen to the 4-position. 

Tire and NMR parameters of some 1-alkyl-4-benzimidazolyl-2-idene- (type 72) and l-alkyl-4-(5-methylpyrazolyl-3-idene)-l,4-dihydro pyridines (type 73) were discussed in 89CC1086 and 91JOC4223. Comparison of the shifts for DMSO-dg and CDCI3 solutions with data reported for quaternary pyridinium compounds as well as anionic species in the azole series and data obtained for mesoionic betaines of the azinium azolate class left no doubt that these heterofulvalenes have a betaine character and, therefore, the NMR signals correspond to their dipolar resonance form. 

To the best of our knowledge, the hrst paper which mentioned an A-(l-haloalkyl)pyridinium compound appeared 66 years ago in the Chemische Berichte (Krohnke 33CB1386). Tlie author described the reaction of phenacyl pyridinium derivatives 1 with bromine in acetic acid to give the halides 2 (36CB2006 37CB864). Tire addition of bromine to the double bonds of A-vinylpyridinium salts 3 and 4 giving the adducts 5 and 6 has also been reported (51CB399) (Scheme 1). 

Several N-(chloromethyl)pyridinium platinum complexes have been described in the literature [89JOM255 92JCR(S)296 92JOM155]. Interestingly, 2-pyridyl platinum(II) complexes 11 and 12, having been dissolved in dichloromethane, are slowly N-alkylated by the solvent, yielding the N-(chloromethyl)pyridinium compounds 13 (76%) and 14 (77%) (Scheme 3). 

Theoretical calculations (B3LYP/6-31G ) indicated that in their NMR spectra C(2) and C(9) carbons of n /2ydro-(2-hydroxy-4-oxo-4//-pyrido[l,2-n]pyrimidinium)hydroxide mesoionic forms appeared at significantly higher field (ca. 159-160 ppm and 115-116 ppm, respectively), than in the 2-hydroxy-4//-pyrido[l,2-n]pyrimidin-4-one tautomers (ca. 169-173 ppm and 130 ppm, respectively) (00JCS(P2)2096). C(8) carbon of mesoions (pyridine-y type carbon) appeared at lower field (144-146 ppm) than 6-C (140 ppm, pyridine-o type carbon), as is typical of pyridinium compounds. 

Fig. 10.8 A where the R substituents are alkyl or heterocyclic radicals to give compounds such as cetyltrimethylammonium bromide (cetrimide), cetylpyridinium chloride and benzalkonium chloride. Inspection of the stmctures of these compounds (Fig. 10.8B) indicates the requirement for good antimicrobial activily of having a chain length in the range Cg to Cig in at least one of the R substituents. In the pyridinium compounds (Fig. 10.8C) three of the four covalent links may be satisfied by the nitrogen in a pyridine ring. Polymeric quaternary ammonium salts such as polyquatemium 1 are finding increasing use as preservatives.

Wright KA, RB Cain (1972) Microbial metabolism of pyridinium compounds. Metabolism of 4-carboxy-l-methylpyridinium chloride, a photolytic product of paraquat. Biochem J 128 543-559. 

N-(p-dodecylphenyl)-2,4,6-trimethylpyridinium sulfoacetate is suitable as an inhibitor in aqueous media [606]. Such pyridinium compounds exhibit greater thermal stability than N-aralkyl pyridinium compounds or N-alkyl pyridinium compounds. Therefore the desired properties are retained both during and after exposure to elevated temperatures. 

Flat-oriented bipyridinium compounds adsorb with additional stabilization compared to flat-oriented mono-pyridinium compounds, due to charge transfer interactions and resonance stabilization in linked aromatic rings versus single pyridinium ions. Although... 

Fig. 8.15. Resonance forms that show why the dihydropyridine pro-pro-moiety (A) is less susceptible to alkaline and enzymatic hydrolysis than the pyridinium pro-moiety (B). Electron donation from the ring to decrease the electrophilicity of the carbonyl C-atom is possible for A but not for the pyridinium compound B. 

A further condition for good brain delivery, one that is particularly relevant in the present context, is that e) direct hydrolysis of the dihydropyridine pro-prodrug (Fig. 8.14, Reaction c) does not compete with oxidation, especially in the periphery, since this would decrease the amount of CDS available for brain delivery. In fact, the pyridinium metabolite is more susceptible than the dihydropyridine pro-prodrug to alkaline and enzymatic hydrolysis, since the carbonyl C-atom of the pyridinium compound (B, Fig. 8.15) is much more electrophilic than that of the dihydropyridine (A, Fig. 8.15). 

As previously mentioned, amphoteric surfactants presently represent a minor fraction of the total surfactants production with only specialty uses. They are compounds with both anionic and cationic properties in aqueous solutions, depending on the pH of the system in which they work. The main types of these compounds are essentially analogs of linear alkane sulfonates, which provide numerous points for the initiation of biodegradation, and pyridinium compounds that... 

Alkylpyridines supposedly lie also along another biosynthetic route, affording pofymeric pyridinium compounds in marine haliclonid sponges the Indo-Pacific Callyspongia fibrosa (Davies-Coleman 1993), the Caribbean Amphimedon compressa (Albrizio 1995), and the Mediterranean Reniera sarai (Sep5i6 1997). 

There is also a distinct tendency toward oxidation in the a-position of 4-alkyl substituents in pyridinium compounds in the case of bis- and... 

Quinolinium salts react similarly to pyridinium compounds when oxidized. N-Alkylated salts 142, for example, yield only 2-quinolones 143 after Decker oxidation. 4-Quinolones 144 cannot be isolated (1892CB443 70HCA1903). 

A class of acylpyridinium salts that has been investigated quantitatively is the carbamoyl pyridinium compounds. Diphenylcarbamoyl-pyridinium chloride was synthesised in 1907277. l-(N,N-Dimethylcarbamoyl)-pyridinium chloride (XLVI) was found by Johnson and Rumon278 to decompose to its component parts in non-hydroxylic solvents, dielectric constants from 5 to 95, viz. 

Pyridinium enolbetaines and cyclopropenones have been used as the three carbon atom components in a further illustration of type (ii) syntheses <71LA(746)102). The betaine is formed in situ by deprotonation of a pyridinium salt and good yields of the pyranone result simply on boiling in methanol solution. Considerable variation in the substituents is possible and triphenylphosphonium or diethylsulfonium enolbetaines may be used in place of the pyridinium compound. 

---