Herbert Bartsch

Stability indicating assays for the determination of piroxicam—comparison of methods☆

Photodegradation of piroxicam, a 1,2-benzothiazine oxicam, is studied laying special emphasis on the investigation of the correlation between concentration of the sample solution and stability. A comparison of three different methods (HPTLC/densitometry, HPLC, CE) developed for the photostability testing of the title compound is presented. The stability indicating capability of the assays is proved using forced degradation by exposing a sample solution to artificial irradiation from a xenon source. The chromatograms and the electropherogram of the resulting solution show piroxicam well resolved from the degradation products. For quantitation external calibration is employed, all calibration curves being linear in the respective concentration range of interest. Piroxicam solutions of three different concentrations (2 mg ml(-1); 250 microg ml(-1); 40 microg ml(-1)) are subjected to simulated sunlight for 480 min. The stability is investigated by quantitation of piroxicam by the methods mentioned. The methods are compared in respect of performance and precision. Costs and time of analysis are regarded also.

The Lawesson reagent as selective reducing agent for sulfoxides

Abstract Different functionalized sulfoxides can be selectively deoxygenated by Lawesson reagent to yield the corresponding sulfides in high amounts.

SELECTIVE ASSAYS FOR QUANTITATION OF TENOXICAM IN PRESENCE OF ITS PHOTODEGRADATION PRODUCTS

ABSTRACT Tenoxicam, a thienothiazine oxicam, is a potent anti- inflammatory and antirheumatic drug. A comprehensive study on the photostability of tenoxicam is presented, including a comparison of three different methods (HPTLC/densitometry, HPLC, CE) developed for the photostability testing of the title compound. The stability indicating capability of the respective assays is proven with sample solutions forcedly degraded by artificial irradiation from a xenon source. The chromatograms and the electropherogram of the resulting solution, show tenoxicam well resolved from the degradation products. The methods are applied for testing the photostability of solutions containing tenoxicam in various concentrations (2 mg mL−1; 250 μg mL−1; 40 μg mL−1), and stored under different conditions. The stability of tenoxicam was found to be dependent on the nature of the light source, as well as on the concentration of the sample solution. The assays are validated and compared with respect to performance and precision.

Synthese und Reaktivität von 2- und 3-hydroxylierten Dihydro-1,4-Benzoxazinen

Abstract2 can be pyrrolized to yield3 a, which in turn may be hydrolyzed with HCl to3 b. Acetylation of3 a followed by a reaction with trifluoroacetic acid (TFA) gives3 e. Elimination of ethanol from3 a or of water from3 e is not possible. Treatment of1 a with pyridine/acetic anhydride andTFA or with acetic acid/acetic anhydride affords4 a and4 b, resp. Reaction of4 b in benzene/p-toluenesulfonic acid for 2 hours yields both ethers5I and5II, whereas after 6 hours 4-acetyl-4H-1,4-benzoxazine (6) is obtained. The structures of all products are established by chemical and spectroscopic methods.

Comparison of analytical methods for investigating the photostability of isoxicam

Abstract A comparison of three different methods (HPTLC–densitometry, HPLC, CE) developed for the photostability testing of isoxicam is presented. The stability indicating capability of the assays is proved using forced degradation by exposing a sample solution to artificial irradiation from a xenon source. The chromatograms and electropherogram of the resulting solution show isoxicam well resolved from the degradation products. For quantitation, external calibration is employed, all calibration curves being linear in the respective concentration range of interest. Photodegradation of isoxicam is studied with special emphasis on the investigation of the correlation between concentration of the sample solution and the stability. Isoxicam solutions of three different concentrations (2 mg ml −1 ; 250 μg ml −1 ; 40 μg ml −1 ) are subjected to simulated sunlight for 480 min and tested for stability. The methods are compared in respect of performance, precision, detection and quantitation limits.

Der Einfluß von Stickstoffsubstituenten bei der Synthese von 3-Methyl-1,4-Benzoxazinen

Starting from1 the azomethine2 is obtained. The intermediates4 a and4 b of this reaction sequence cause the high yields. Cyclization of theN-alkylderivatives4 d and8 b leads also to an azomethine, which is obtained as its salt11. Cyclization of theN-acetylderivative13 yields however the anamine14. The structures of the new products are established by chemical and spectroscopic methods.

Untersuchungen zur Synthese neuer tricyclischer Heterocyclen aus 1,4-Benzoxazin- und 1,4-Benzothiazin-3-oximen. 7. Mitteilung über Studien zur Chemie von O,N- und S,N-haltigen Heterocyclen

SummaryThe behaviour of amidoximes3 and4 under cyclization conditions is reported: Reaction with carbonyldiimidazole yields oxadiazolobenzoxazine11 and oxadiazolobenzothiazine12, respectively.

Studies on the chemistry of 1,4-oxazines, XV: Synthesis of ethyl 3,4-dihydro-4-tosyl-2H-1,4-benzoxazine-3-carboxylate

A four step synthesis of ethyl 3,4-dihydro-4-tosyl-2H-1,4-benzoxazine-3-carboxylate (4) from the acetal5 is described.ZusammenfassungEine Synthese des 3,4-Dihydro-4-tosyl-2H-1,4-benzoxazin-3-carbon-säureethylesters (4) über vier Stufen wird, ausgehend vom Acetal5, beschrieben.

Eine neue Synthese des Pyrrolo[3,2,1-hi]indol-Systems Studien zur Synthese von 1,4-Oxazinen, 1. Mitt

Reaction of diphenacylaniline (1) withPPA yields in dependence of reaction time the indole3 and the pyrroloindole4. The structures were established on the basis of spectroscopic methods. Action of LiAlH4 on4 forms5 by hydrogenation of one double bond and cleavage of one pyrrole ring.

Studies on ring opening reactions of β-lactams

Abstract Reaction of tricyclic azetidinones 1–5 (azetobenzoxazine, -thiazine, -thiazepine and -azepine derivatives) with trifluoroacetic acid led to bicyclic thioesters 6–13 . There is evidence for an intermolecular reaction, a possible mechanism is discussed. The structure of two representative thioesters ( 8 and 9 ) was elucidated by different NMR experiments, complete assignments of 1 H- and 13 C-chemical shifts are given. Reaction of the azetobenzoxazine 2 with sodium periodate and magnesium monoperoxyphthalate led to the sulfoxide 18 and the sulfone 19 , respectively.