Derivatives pyrazine

In deuterochloroform, pyrazine shows a single proton resonance at S 8.59 (72CPB2204). Vo, Vm and Vp values between pyrazine ring protons obtained from a number of pyrazine derivatives are 2.5-3, 1.1-1.4 and 0 Hz respectively, and these values do not appear to be affected by the nature of the ring substituents. Some substituent shielding parameters are shown in Table 1. 

A large body of information is available on the UV spectra of pyrazine derivatives (B-61MI21400, B-66MI21400). Pyrazine in cyclohexane shows two maxima at 260 nm (log e 3.75) and 328 nm (log e 3.02), corresponding to ir->ir and n ir transitions respectively (72AHC(14)99). Auxochromes show similar hypsochromic and bathochromic shifts to those observed with the corresponding benzenoid derivatives. 

The cleavage of fused pyrazines represents an important method of synthesis of substituted pyrazines, particularly pyrazinecarboxylic acids. Pyrazine-2,3-dicarboxylic acid is usually prepared by the permanganate oxidation of either quinoxalines or phenazines. The pyrazine ring resembles the pyridine ring in its stability rather than the other diazines, pyridazine and pyrimidine. Fused systems such as pteridines may easily be converted under either acidic or basic conditions into pyrazine derivatives (Scheme 75). 

Before the discovery of streptomycin, pyrazinamide (126) was one of the front runners in the treatment of tuberculosis. A broad spectrum of biological activity has been associated with pyrazine derivatives, ranging from the herbicidal activity of (127) to antibiotic activity... 

The stereochemistry and conformational behaviour of 2,3-dimethyl-l,2,3,4-tetrahy-dropyrido[2,3-f ]pyrazine and some related compounds have been studied, as have the corresponding pyrido[3,4-f ]pyrazine derivatives (67JOC1378, 60JA3762). 

Examination of the pyrazino[2,3-rf]pyrimidine structure of pteridines reveals two principal pathways for the synthesis of this ring system, namely fusion of a pyrazine ring to a pyrimidine derivative, and annelation of a pyrimidine ring to a suitably substituted pyrazine derivative (equation 76). Since pyrimidines are more easily accessible the former pathway is of major importance. Less important methods include degradations of more complex substances and ring transformations of structurally related bicyclic nitrogen heterocycles. 

Despite the fact that one of the first pteridine syntheses was based on an intramolecular Hofmann carboxamide degradation of pyrazine-2,3-dicarboxamide by action of potassium hypobromite and leads to lumazine (equation 104), (07CB4857), pyrazine derivatives in general have not often been used because of availability problems. The reaction of alkyl... 

Methoxylation of 2,5- and 2,3-dibromopyrazines provides the basis for a comparison of ortho and para direct deactivation (Section II, E, 2, e) in the mono-methoxy derivatives such as 198 and 199. Pyrazine derivatives are discussed in Sections II, C and II, D. 

The adverse properties of red beet preparations are without doubt, their high nitrate content, their unpleasant smell due to pyrazine derivatives and geosmin with a low odor threshold, and finally the risk of carry-over of earth-bound germs. - " Since nitrate has been associated with nitrite and nitrosamine formation, the latter exhibiting cancer-inducing properties, procedures have been developed to reduce the nitrate content of red beet preparations. This has been achieved by microbial denitrification. - ... 

Some bacteria can give products a rancid smell others can impart the "sweet" odour of dirty drains by the production of certain pyrazine derivatives. Other bacteria, known as sulphate reducers, for example Desulphovibrio desulphuricans, are able, under anaerobic conditions, to utilise oxygen from sulphates leading ultimately to the formation of hydrogen sulphide. Opperman and Goll (1984) in their study of contaminated emulsion paints concluded that more than a quarter were infected with these and other anaerobic organisms. 

High density brine completion fluids also often require the use of corrosion inhibitors (8,9). Blends of thioglycolates and thiourea alkyl, alkenyl, or alkynyl phosphonium salts thiocyanate salts mercaptoacetic acid and its salts and the reaction products of pyridine or pyrazine derivatives with dicarboxylic acid monoanhydrides have been used as high density brine corrosion inhibitors. 

The l,2,5-oxadiazolo[3,4-< ]pyrrolo[l,2- ]pyrazine derivative 185 was synthesized from the cr-chloroketone 184 and diaminooxazole 183. Some dihydro product 186 was also isolated (Equation 45) <1999CHE882>. 

Analogous photoadditions have been observed on irradiation of pyrimidine and purine bases in ethers and amines. Irradiation of 1,3-dimethylur-acil (314) in tetrahydrofuran leads to the formation of 5- and 6-(tetrahydro-furan-2-yl)-5,6-dihydrouracils 315 and 316.261 Similarly, solvent adducts arising by way of initial hydrogen abstraction have been obtained on irradiation of pyrazine derivatives in diethyl ether or tetrahydrofuran.262 The... 

Scheme 7.85 Fluorous phase synthesis of imidazo[l,2-a]pyridine/pyrazine derivatives.

Novel pyrazine-containing cydoadducts 80a-c were synthesized by Diels-Alder reaction of [60]fullerene with the corresponding 2,3-bis(bromomethyl)pyrazine derivatives 79a-c (Scheme 9.23) [73] the 2,3-pyrazinoquinodimethanes were trapped as the Diels-Alder adducts by reaction with [60]fullerene under reflux in o-dichloroben-zene (ODCB) as solvent with classical heating and under the action of microwave ir-... 

Selective reduction of the 7-oxo group in pyrido[23-synthetic approach to 5,10-dideazatetrahydrofolic acid <00H(53)1207>. Cycloaddition of pyrimido[4,5-c][l,2,5]oxadiazine 96 with 2,3-dihydrofuran affords a new synthesis of dimethyllumazine derivative 97 which undergoes a ring-opening reaction to give pyrazine derivative 98 <00JHC419>. 

For the practical application to nonlinear optics, further, noncentrosymmetric LB films are required to possess not only large nonlinear optical response but excellent optical quality and thickness appropriate to optical devices. In this study, a family of pyrazine derivatives was found to be an LB film-forming material applicable to waveguide devices. The optical nonlinearity in the pyrazine LB films and the application of the pyrazine LB films to a frequency-doubling waveguide device is demonstrated in the latter part. 

Second-order nonlinear optical properties of noncentrosymmetric LB films composed of pyrazine derivatives... 

For the fabrication of noncentrosymmetric LB films, a two-compartment Langmuir trough, of which detail is given in the section 1.4, was used. Monolayers of pyrazine derivatives and arachidic add were spread on each compartmentalized subphase (BaC or CdCl aqueous solution, 2 x 10"4 M). The monolayers were compressed to 30 mNm 1, and then monolayers of pyrazine derivatives and arachidic acid were deposited fused quartz substrates in up stroke and down stroke, respectively. The aggregation structure in the LB films was studies by the absorption spectra and X-ray diffraction. 

By comparison with an octadecyloxy stilbazium iodide monolayer (x<2> = 0.51 x 10"6 esu) [15], the value of the effective second-order susceptibility x r at 45° incidence was estimated to be 1.0 x 10"7 esu. The value is fairly large, in comparison with those of the conventional nonlinear optical materials (e.g. LiNbOs). Other pyrazine derivatives (C120PPy and C12SPPy) also gave thick noncentrosymmetric LB films with fairly large second-order nonlinearity by the alternating deposition with arachidic acid. The estimated Xeff values of the pyrazine LB films are listed in Table 3. 

Second-order nonlinear optical waveguide using noncentro-symmetric LB film of pyrazine derivative... 

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