L-Hydroxy-3-imidazolines

In electrochemical oxidation of l-hydroxy-3-imidazoline-3-oxides containing one to four H atoms at a-C, one observes in ESR-spectra not only triplet splitting of the nucleus 14N of the nitroxyl group (a v 15-16 G) but also splitting of the neighboring protons (a// 18-20 G), with multiplets corresponding to their number (from doublet to quintet) (101). Unlike spatially hindered hydroxylamines which show reversibility in electrochemical oxidation, hydroxylamines with H at a-C are oxidized irreversibly. Oxidation of hydroxylamines with nitroxyl radical proceeds easily and with quantitative yields (102). In the oxidation of asymmetric polylluorinated hydroxylamines with Mn02, isomeric polyfluorinated nitrones have been obtained (103). 

On studying electrochemical properties of l-hydroxy-3-imidazoline-3-oxides and their conversion into nitronyl nitroxyl radicals (NNR), the intermediate production of a nonaromatic radical cation (220) of AH -imidazole-1,3- dioxides (219) (Scheme 2.78) (101) was suggested. 

Reduction of nitrone groups to hydroxylamines occurs readily with sodium borohydride (201). In particular, the action of NaBHj on l-hydroxy-3-imidazoline-3-oxides (268) leads to 1,3-dihydroxyimidazolidines (269), which on subsequent treatment with hydroxylamine hydrochloride afford 1,2-bishydroxyl-amines (270) (Scheme 2.99) (478). 

Oxidation gives stable radicals (442) which form cycloadducts with dipolarophiles (e.g. 443) (85TL4801). Radicals formed from 3-imidazoline 1-oxides or l-hydroxy-3-imidazolines can be formylated on nitrogen under Vilsmeier conditions and exocyclically brominated or chlorinated by NBS or NCS on a 4-methyl group. 

When l-hydroxy-3-imidazoline 3-oxides (263) are treated with HCl they dehydrate forming imidazole 3-oxides (Scheme 153) (73CHE1175). Reduction of 4//-imidazole N-oxides with borohydride leads to either 1-hydroxy-imidazolines or -imidazolidines, depending on the position of the oxide function. Under the same conditions 4//-imidazole 1,3-dioxides give 1,3-dihydroxyimidazolidines (76CHE1280). The 4iT-imidazole AT-oxides are prepared by heating 5,5-disubstituted l-acyloxy-3-imidazoline 3-oxides in vacuo. 

H(14)1313, 90JOC1772). Substituents also affect the equilibrium between l-hydroxy-3-imidazoline 3-oxides and the open-chain hydroxyiminonitrones electron-withdrawing groups in the... 

The formation of l-hydroxy-3-imidazolines proceeds under mild weakly alkaline or weakly acidic conditions, in contrast to the strongly acidic media usually employed for obtaining precursors of doxyl radicals (Keana, 1978). l-Hydroxy-3-imidazolines are easily oxidized to nitroxides by molecular oxygen, Pb02, Mn02, etc. 

Treatment of l-hydroxy-3-imidazoline-3-oxides (6a,c) with Grignard reagent opens the cycle and forms 1,2-iV-t rt-butylhydroxylaminooximes (38a,c). Oxidation of the latter leads to acyclic stable nitroxides (39a,c)... 

Dissociation of molecular ions of l-hydroxy-3-imidazoline-3-oxides (6) (Scheme 4) and of corresponding nitroxides (7) (Scheme 5) proceeds in a more complicated manner (Ivanovskaja et al, 1979). 

Easy transformation of 1,2-hydroxylaminoketones to l-hydroxy-3-imidazolines and then to nitroxides allowed introduction of a nitroxyl group into molecules containing a ketone group, similar to the method suggested by Keana et al (1967). The method of Keana is based on the condensation of a compound containing a ketone group with 2-amino-2-methylpropanol-l in the presence of p-toluenesulfonic acid and subsequent oxidation of the resulting oxazolidine derivative with m-chloroper-... 

Synthesis of l-hydroxy-3-oxyimidazolines from a-hydroxylaminooximes has been reviewed " . Therefore, in the present work it will be described very briefly. In general, the reaction of oximes 136 with aldehydes, ketone or triethyl orthoformate leads to imidazolines 137 or 138, respectively (equation 60). 

On the basis of UV measurements it has been shown that l-hydroxy-2-imidazolines exist in equilibrium with 2-imidazoline 3-oxides (76CHE1280). 

Another taste modifier, A-(l-methyl-4-hydroxy-3-imidazolin-2,2-ylidene)-alanine (61 Fig. 3.35), was already isolated earlier [87]. Its formation can be explained by a thermal reaction between creatinine and lactic acid or alanine, compounds which are also present in process flavourings. 

About 10 years ago iV-(l-methyl-4-hydroxy-3-imidazolin-2,2-ylidene)alanine was isolated from beef broth and reported to impart a brothy, thick sour taste as characteristic taste impression of beef bouillon (7). Although this compounds has been suggested to be formed from the reaction between creatinine and lactic acid, neither the formation pathways, nor the human threshold concentration for the sensory activity of that molecule was yet confirmed. In order to answer the question as to whether this taste modulator might be formed by Maillard-type reactions of creatinine, the objective of the present investigation was to screen for taste modulating creatinine glycation products in heated creatinine/ribose solutions and to investigate the sensory activity of these derivatives. Furthermore, LC-MS/MS studies should be performed to verify the natural occurrence of the identified taste modulators in beef stock. 

Polarization of the C=N bond also causes electrophilic substitution of the alkyl group hydrogen in the a-position. Interaction of 1-hydroxy-3-imidazoline-3-oxide (6a) with aromatic aldehydes in the presence of bases, similar to the case observed for heterocyclic iV-oxides (Ochiai, 1967 Katritzky and Lagowski, 1971 Hansen and Boyd, 1970), leads to l-hydroxy-4-arylvinyl-3-imidazoline-3-oxides (41), oxidation of which generates nitroxides 42. The action of an equimolar amount of amyl nitrite on l-hydroxy-4-methyl- and l-hydroxy-4-ethyl-3-imidazoline-3-oxides... 

Imidazolin-2-one, 1,5-diphenyl-4-aryl-synthesis, 5, 492 4-Imidazolin-2-one, 1-hydroxy-synthesis, 5, 474—475 4-Imidazolin-2-one, l-methyl-3-phenyl- C NMR, 5, 355 Imidazolinones acylation, 5, 424, 443 alkylation, 5, 443 developers... 

Many mercaptoazoles exist predominantly as thiones. This behavior is analogous to that of the corresponding hydroxyazoles (cf. Section 3.4.3.7). Thus oxazoline-, thiazoline- and imidazoline-2-thiones (677) all exist as such, as do compounds of type (678). However, again analogously to the corresponding hydroxy derivatives, other mercaptoazoles exist as such. 5-Mercaptothiazoles and 5-mercapto-l,2,3-triazoles (679), for example, are true SH compounds. 

A comparison of the reactivity of C-N or C-P fission in P-lactams and four-membered cyclic phosphonamidates, respectively, shows the latter to be much more reactive (95PAC711). The absolute configuration of some 1,3,4-trisubstituted P-Iactams is determined by CD spectra (95TL4217). A ring expansion of 3-amido-l-hydroxy-p-lactams to 4-imidazolin-2-ones by the action of tosyl chloride and organic base is reported (95TL1617). 

The preparation of l-hydroxy-2-(2-nicotinic-3-methoxycarbonyl)-4-isopropyl-4-methyl 2-imidazolin-5-one, (IV), is described. 

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