Thiobarbituric acid preparation

Barbituric acid and 2-thiobarbituric acid are readily prepared by the condensation of diethylmalonate with urea and thiourea respectively, in the presence of sodium ethoxide. The use of substituted derivatives of urea and thiourea and of diethyl malonate will clearly lead to a wide range of barbituric and thiobarbituric acids having substituents in the i, 3, or 5 positions. 

Analytical Techniques. Sorbic acid and potassium sorbate are assayed titrimetricaHy (51). The quantitative analysis of sorbic acid in food or beverages, which may require solvent extraction or steam distillation (52,53), employs various techniques. The two classical methods are both spectrophotometric (54—56). In the ultraviolet method, the prepared sample is acidified and the sorbic acid is measured at 250 260 nm. In the colorimetric method, the sorbic acid in the prepared sample is oxidized and then reacts with thiobarbituric acid the complex is measured at - 530 nm. Chromatographic techniques are also used for the analysis of sorbic acid. High pressure Hquid chromatography with ultraviolet detection is used to separate and quantify sorbic acid from other ultraviolet-absorbing species (57—59). Sorbic acid in food extracts is deterrnined by gas chromatography with flame ionization detection (60—62). 

When 1, 3, 3-triethoxypropene was hydrolyzed with IN sulfuric acid, a solution of malonaldehyde whose optical density was perfectly stable at 350 m/x for at least one week was obtained. If the solution was made alkaline, the optical density at the same wavelength increased by a small value and then remained virtually constant for at least one week (56). It was also observed that in these solutions the extinction coefficient at 350 m/x was very low (observed 8.3, 61.5 and 69, for solutions of pH 0.4, 7.15 and 9.4 respectively) compared with previously reported values which varied from 200 ( 40) to 1000 ( 48). On the other hand, the absorption of solutions having a pH of 3 to 5, increased considerably with time (at pH 4.75, the extinction coefficient of malonaldehyde at 350 m/x was initially about 40 after four weeks a value of about 930 was recorded and the optical density of the solution was still increasing). This increase in absorption was accompanied by a marked decrease in the malonaldehyde content of the solution, as measured by the thiobarbituric acid method. As a corollary, it was found that aqueous solutions of malonaldehyde, prepared by autocatalyzed hydrolysis (33) of the same acetal and which had a pH of about 3.5, showed, at the completion of the hydrolysis, considerably higher extinction coefficient values at 350 m/x than did those malonaldehyde solutions which were prepared by hydrolysis with IN acid and subsequently adjusted to pH 4. It appears, therefore, that at pH values at which most of the periodate oxidations are carried out, malonaldehyde is unstable and undergoes a chemical reaction, the nature of which is not, as yet, known. 

Hassoun et al. (1993) examined the effects of various pesticides on lipid peroxidation and DNA single strand breakage in the hepatic cells of female Sprague-Dawley rats. Animals were dosed orally once with endrin at 4.5 mg/kg, lindane at 30 mg/kg, chlordane at 120 mg/kg, or DDT (dichlorodiphenyl trichloro-ethane) at 40 mg/kg, or vehicle only (com oil, control). At 6, 12, and 24 hours post-dosing, 4 animals from each group were sacrificed, their livers removed, and prepared for lipid peroxidation assay. Lipid peroxidation was measured calorimetrically by determining the amount of thiobarbituric acid reactive substances (TBARS) formed. Exposure to endrin resulted in a 14.5% increase in hepatic mitochondrial... 

Nickel boride, formed in situ from sodium borohydride and nickel chloride, has been used to prepare dihydro derivatives from thiothymine 385 <2001JME1853> and thiobarbituric acid derivatives 388 <2002J(P1)2520>. With 4-thiothymine derivatives, an isomeric mixture of 3,4- and 3,6-dihydro derivatives 386 and 387 was obtained <2001JME1853>, but with 2-thiobarbiturates, clean reduction at the 2-position was able to be achieved <2002J(P1)2520>. 

Antioxidant activity was also tested in a liver microsome system. In this study, mice were treated by oral intubation (2 times/wk) with 0.2 ml olive oil alone or containing CLA (0.1 ml), linoleic acid (0.1 ml), or dl-a-tocopherol (lOmg). Four weeks after the first treatment, liver microsomes were prepared and subsequently subjected to oxidative stress using a non-enzymatic iron-dependent lipid peroxidation system. Microsomal lipid peroxidation was measured as thiobarbituric acid-reactive substance (TBARS) production using malondialdehyde as the standard. It was found that pretreatment of mice with CLA or dl-a-tocopherol significantly decreased TBARS formation in mouse liver microsomes (p < 0.05) (Sword, J. T. and M. W. Pariza, University of Wisconsin, unpublished data). 

A promising new method for the preparation of thiobarbituric acids (112) involving the reaction of carbon suboxide with various arylthio-ureas was reported by Baranova et al.2il... 

Dave and Shah have reported a Gould-Jacod type reaction for the microwave-assisted synthesis of thieno[3,2-e]pyrimido[ 1,2-c]pyrimidines via intermediate thieno[2,3-d ] pyrimidines (Scheme 3.46)73. A one-pot synthesis of pyrano [2,3-d]pyrimidines was also described by Kidwai and co-workers starting from thiobarbituric acids. The thio-barbituric acid intermediates were also prepared by microwave heating, using basic alumina as the solid support (Scheme 3.46)74. 

The standard curve is set up from malonyldialdehyde prepared from freshly hydrolysed malonyldialdehydebisacetal the standard (1 g/ml) is diluted 1 1000 in phosphate-buffered saline and diluted again 1 1000 to a working concentration of 1 ng//d. Tubes containing a range of aliquots from the diluted stock, ranging from 100 fA up to 500 fA, were brought up to a volume of 0.8 ml and then the thiobarbituric acid and the trichloroacetic acid added as described above for the samples. 

Vreman, H.J., Wong, R.J., Sanessi, C.A., Dennery, P.A., Stevenson, D.K. (1998). Simultaneous production of carbon monoxide and thiobarbituric acid reactive substances in rat tissue preparations by an iron-ascorbate system. Can. J. Physiol. Phamacol. 76 1057-65. 

Many methods for the preparation of pure serum albumin are available, and some can be scaled down from techniques used by blood transfusion services to process protein components from outdated blood. Assay can be by affinity chromatography (GlOa), HPLG, isoelectric focusing, mobile affinity electrophoresis, and thiobarbituric acid photometry (NIO). The last method employed acid (pH 1) hydrolysis for 8 hours at 115°C to liberate the... 

In this study 5-(Quinoline-2-ylidene)-l,3-diethyl-2-thiobarbituric acid have been synthesized via Knoevenagel condensation reaction, the product solutions were prepared lO -lO M in CHCI3, THF, MeOH, DMF and DMSO. UVA IS spectra recorded and then compared at each other. Absorbance of the solutions were measured at 200-300 nm. The maximum absorbance value increased and a new absorption appeared at 400-500 nm. The samples were excited at 337 nm in order to measure fluorescence. The maximum emission was observed in MeOH at 398 nm. These values increased by time therefore, the samples were not stable in solution state. 

A one-pot synthesis of pyrimido[4,5-i]quinolines 330 under MWI involved the reaction of l,3-diaryl-2-thiobarbituric acids 329, the appropriate aldehyde, and A-methylaniline to give 72-88% yields after 2 min, compared to 1.5-2 h under conventional thermal conditions. However, compounds 330 were prepared by cyclizing the arylidene derivatives 331 with iV-methylaniline under MWI for 2-5 min (Scheme 67) (97JCR(S)266). 

One of the earliest reports of microwave-assisted organometallic synthesis involved the preparation of arylmercuric chlorides. Heating an ethanol solution of diphenyldiazene and 2-phenylpyridine with Hg(OAc>2 inside a sealed Teflon vessel led to the formation of the desired arylmercury complexes. Yields were a little lower than conventional approaches, but reaction times were at least 30-times shorter. This chemistry was extended 10 years later when a solvent-free method was developed. Arylmercuric chlorides together with benzoquinone, barbituric acid, or thiobarbituric acid were adsorbed on basic alumina before being exposed to microwave irradiation for 1-3 min to produce derivatives (YIF = 1.3-1.5). 

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