Al-pyrroline

Fig. 1.3 Reactions showing synthesis of glutamate in brain. Aspartate aminotransferase (1) glu-taminase (2) glutamate dehydrogenase (3) GABA aminotransferase (4) alanine aminotransferase (5) ornithine aminotransferase (6) Al-pyrroline 5-carboxylic acid dehydrogenase (7) and asparagine synthetase (8)...

Cylokinin oxidasc. dchydrogaiasc 64 Al-Pyrroline-5-carboxylate synthetase 100... 

Peddibhotla, S., Tepe, J. J. (2004). Stereoselective synthesis of highly substituted Al-pyrrolines exo-Selective 1,3-dipolar cycloaddition reactions with azlactones. Journal of the American Chemical Society, 126, 12776-12777. 

The simplest compounds, -pyrroline and -piperideine,donotexistin the monomeric form. Schdpf et al. (29S) described two geometric isomers of J -piperideine trimer and called them a- and -tripiperideines (182). An equilibrium exists between A -piperideine and both trimers which, therefore, react as typical aldehyde ammonia. The trimer rearranges at pH 9-10 in an almost quantitative yield to isotripiperideine (183) which, in turn, is in equilibrium with tetrahydroanabasine (184) and -piperideine. 

The regioselectivity observed in these reactions can be correlated with the resonance structure shown in Fig. 2. The reaction with electron-rich or electron-poor alkynes leads to intermediates which are the expected on the basis of polarity matching. In Fig. 2 is represented the reaction with an ynone leading to a metalacycle intermediate (formal [4C+2S] cycloadduct) which produces the final products after a reductive elimination and subsequent isomerisation. Also, these reactions can proceed under photochemical conditions. Thus, Campos, Rodriguez et al. reported the cycloaddition reactions of iminocarbene complexes and alkynes [57,58], alkenes [57] and heteroatom-containing double bonds to give 2Ff-pyrrole, 1-pyrroline and triazoline derivatives, respectively [59]. 

The syntheses of flavanoid alkaloids also rest on A-l-pyrroline chemistry and on Friedel-Crafts-type reactions. In Govindachari s pioneering synthesis of ficine (167), pyrrolidine 126 is formed by condensation of trimethoxybenzene and y-aminobutyric acid in the presence of PPA (Scheme 19). Although the mechanism of this reaction has not been precisely determined, it may involve a A-l-pyrrolinium cation. These conditions were later used by Koch et al. in their synthesis of vochysine (Scheme 20) (108). 

The flash vacuum pyrolysis of isopropylidene N./V-disubstituted ami-nomethylenemalonates (e.g., 1235, 1237) was studied by McNab et al. [83CC957 85CC213 86JCS(P1)1465 87CC138 88JCS(PI)863, 88JCS(P1)869, 88JCS(P2)759], They obtained 1,5,5-trisubstituted 2-pyrrolin-4-ones (e.g., 1236, 1238) in 38-75% yields. 

In addition to the two asymmetric syntheses above described, two racemic syntheses of tetraponerines based on the 5=6-5 tricyclic skeleton have been published. Thus, Plehiers et al. [199] have reported a short and practical synthesis of ( )-decahydro-5Tf-dipyrrolo[l,2-a r,2/-c]pyrimidine-5-carbonitrile (238), a pivotal intermediate in the synthesis of racemic tetraponerines-1, -2, -5 and -6, in three steps and 24% overall yield from simple and inexpensive starting materials. The key reaction of the synthesis was a one-pot stereoselective multistep process, whereupon two molecules of A pyrroline react with diethylmalonate to afford the tricyclic lactam ester 239, possessing the 5-6-5 skeleton (Scheme 10). Hydrolysis of the carboethoxy group of 239 followed by decarboxylation yielded lactam 240, that was converted into a-aminonitrile 238 identical in all respects with the pivotal intermediate described by Yue et al. [200] in their tetraponerine synthesis. 

Further investigations on the acceptor-donor system arene-amine have been made by Sugimoto et al. They have reported that direct irradiation of 9-(cu-anilinoalkyl)phenanthrenes give spirocyclic pyrroline derivatives, invoked by... 

In this type of spin traps, 5,5-dimethyl-l-pyrroline-Af-oxide (DMPO) deserves particular mention. DMPO is widely employed as a spin trap in the detection of transient radicals or ion-radicals in chemical and biological systems (see, e.g., Siraki et al. 2007). Characteristic ESR spectra arising from the formation of spin adducts are used for identification of specific spin species. In common opinion, such identification is unambiguous. However, in reactions with superoxide ion (Villamena et al. 2004, 2007b), carbon dioxide anion-radical (Villamena et al. 2006), or carbonate anion-radical (Villamena et al. 2007a), this spin trap gives rise to two adducts. Let us consider the case of carbonate anion-radical. The first trapped product arises from direct addition of carbonate anion-radical, second adduct arises from partial decarboxylation of the first one. Scheme 4.25 illustrates such reactions based on the example of carbonate anion-radical. 

Racemic methadone (MET) is administered to heroin addicts as a substitution therapy. However, methadone enantiomers possess different pharmacological effects, and the drug has been demonstrated to be enantioselectively metabolized to its two major metabolites, 2-ethylidene-l,5-dimethyl-3,3-diphenylpyrrolidine (EDDP) and 2-ethyl-5-methyl-3,3-diphenyl-l-pyrroline (EMDP). Stereoselective separation of MET, EDDP, and EMDP using an alpha-glycoprotein stationary phase and MS-MS detection was proposed by Kelly et al. [34]. Optimal separation conditions were 20 mM acetic acid isopropanol (93 7, pH 7.4), with a flow rate of 0.9mL/min. 

Pearson et al. (64) developed an approach to the fused bicyclic 3-pyrrolines 328 based on an intramolecular azide-alkene cycloaddition (Scheme 9.64). Azides (327) were heated at various temperamres between 70 and 110°C to afford the... 

Since proline already contains a pyrrolidine ring it provides a potential source of nitrogen heterocyclics in the MaiUard reaction, and a number of proline-con-taining model systems have been examined. Tressl et al. [32] identified more than 120 proline-specific compounds in the reaction of proline or hydroxypro-line with various sugars. These include pyrrolines, pyrroles, pyridines, indolines, pyrrolizines and azepines, but relatively few of the compounds have been identified among food volatiles. 

A fourth possibility is the generation of H202 via oxidation of putrescine (butane-1,4-diamine 2.56). This reaction is catalyzed by copper amine oxidase (E.C. 1.4.3.6). Copper amine oxidases are homodimers in which each unit contains a copper ion and a 1,3,5-trihydroxyphenylalanine quinine co-factor. In plants copper amine oxidases generally oxidize putrescine to 4-aminobutanal (2.57). This latter compound undergoes spontaneous cyclization to A1 pyrroline (2.58), ammonia, and H202, as shown in Figure 2-12 (Medda et al., 1995). 

Tufariello has reviewed his strategy for the synthesis of alkaloids (including necine bases) using the 1,3-dipolar cycloaddition of nitrones to alkenes.5 This work began with the synthesis of ( )-supinidine (7) from 1-pyrroline 1-oxide (see these Reports, Vol. 2, Ch. 4). A related approach has been used by Iwashita et al. in their synthesis of ( )-isoretronecanol (5).6 The stereochemistry of the exo-product (8), formed by regiospecific 1,3-dipolar cycloaddition of 1-pyrroline 1-oxide to dihydrofuran (Scheme 2), was confirmed by its conversion into... 

The low odor threshold (0.1 pg/kg water) of this compound and its odor description as "popcorn-like" (27) agrees with its strong crusty character. Furthermore, the statement of Buttery et al. (27) that "2-acetyl-l-pyrroline seems to be the most potent of the cracker-like group of odor compounds" (which includes 3, 5 and 7 in Figure 1) underlines its importance for the flavor of the white bread crust. 

We recently identified 2-acetyl-l-pyrroline (Acp) with a crackerlike odor as the most intense flavor compound of wheat bread crust (4). Tressl et al. (5) reported that small amounts of this compound were formed when model mixtures containing proline and monosaccharides were heated. 

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