Re-examination of Nucleophilic Substitutionin Chlorokojic Acid

 Chlorokojic acid was reacted with S₂O₃ ²⁻, NO₃ ⁻, N₃ ⁻, I⁻, and SCN⁻. Only the three latter nucleophiles substituted the chlorine atom in the 2-CH₂Cl group of kojic acid. In none of the products nucleophilic substitution at position 6 of the 4-pyrone could be found. Regular substituion of chlorokojic acid with I⁻ (iodokojic acid), N₃ ⁻ (azidokojic acid), and SCN⁻ (thiocyanato and isothiocyanato kojic acids) was accompanied by formation of allomaltol. Reaction pathways for the formation of allomaltol and 6-substituted allomaltol derivatives are proposed. The latter has been formerly discovered in the reaction of chlorokojic acid with secondary amines.     

Formation of Peracetic Acid upon Aging of Perborate in Acetic Acid. Kinetics of the Oxidation of S-Phenylmercaptoacetic Acids

Summary.  Upon aging, perborate in glacial acetic acid generates peracetic acid and thus oxidizes S-phenylmercaptoacetic acid rapidly. Perborate dissolved in ethylene glycol, however, does not show the aging effect, and the corresponding oxidation proceeds smoothly. The oxidation is of second order and not acid catalyzed. Boric acid and borate do not influence the oxidation. In the smooth oxidation, is the reactive species. The oxidation of some para-substituted S-phenylmercaptoacetic acids conforms to the Exner relationship, indicating operation of a common mechanism. Also, the oxidation obeys the Hammett equation with a negative reaction constant. However, the oxidation of p-nitro-S-phenylmercaptoacetic acid follows a different kinetic pathway. Received March 15, 2000. Accepted (revised) May 3, 2000     

Spectroscopic Study of the Conformation of 2-Anilino-2-ethoxy-3-oxothiobutyric Acid Anilides

Summary.  An NMR study of the equilibriummixture of two conformers of 2-anilino-2-ethoxy-3-oxothiobutyric acid anilides 3 allows to estimate their population ratio in solvents of increasing polarity. X-Ray analysis as well as IR spectroscopy confirmed that the conformer present in the solid state is stabilized by two hydrogen bonds. The structural basis of the second conformer observed in solution is the 1,4-type S⋯O interaction between the sulfur of the thioanilide moiety and the oxygen of the ethoxy group with a distance of 2.878 ?. Received May 29, 2000. Accepted (revised) July 14, 2000     

Synthesis and Hemolytic Properties of Glycyrrhetic Acid Glycosides

Summary.  The synthesis of monodesmosidic glycyrrhetic acid disaccharides via its diphenylmethyl ester is described. Their hemolytic activity is lower as compared to the corresponding oleanolic aciddisaccharides. The influence of the structure of the aglycon on the hemolytic activity is discussed. Received November 18, 1999. Accepted November 30, 1999     

Synthesis and Hemolytic Properties of Lactosides of Glycyrrhetic Acid Derivatives

Summary.  The partial synthesis of lactosides of glycyrrhetic acid, its 11-deoxo and 18α-derivatives, and their methyl esters is described. The influence of the aglycon structure on the hemolytic properties of the title compounds is discussed and compared with those of oleanolic acid derivatives. Furthermore, we describe an optimized preparation of 18α-glycyrrhetic acid. Received August 20, 2001. Accepted September 3, 2001     

Determination of Amoxycillin and Clavulanic Acid in Some Pharmaceutical Preparations by Derivative Spectrophotometry

 Derivative spectrophotometry was applied for the simultaneous determination of amoxycillin and clavulanic acid in pharmaceutical preparations: “Augmentin” inj. and tablets and “Amoksiklav” drops and tablets, in solutions after hydrolysis with sodium hydroxide. As the absorption spectra overlap strongly (amoxycillin λ_max = 247 nm and 290 nm, clavulanic acid λ_max = 258 nm) the first and the second derivative spectrophotometric procedure was elaborated for their determination. Amoxycillin was determined at λ = 257.9 nm (1-st derivative spectra) or λ = 273 nm (2-nd derivative) while clavulanic acid at λ = 280.3 nm (1-st derivative) or λ = 285 nm (2-nd derivative spectra). The Beer’s law is obeyed in the range of 0.004–0.04 mg/ml for amoxycillin and 0.002–0.02 mg/ml for clavulanic acid. Received December 6, 1999. Revision August 1, 2000.     

Sulfuric Acid: A Mild Catalyst for the Regioselective Synthesis of 2-Substituted [1,2,4]Triazolo[5,1-b][1,3]thiazin-7-ones

Summary.  A facile and regioselective synthesis of 2-substituted [1,2,4]triazolo[5,1-b][1,3]thiazin-7-ones by action of sulfuric acid on (4H-[1,2,4]triazol-3-ylsulfanyl)-acrylic acids is described. Received January 23, 2001. Accepted (revised) May 7, 2001     

Synthetic Transformations of Abietic Acid V<Superscript>a</Superscript>: Structure Modification and Ozonization

Summary.  Carbon side chains are attached via Reformatsky reactions to the B-ring of abietic acid, followed by selective modifications and finally ozonization of the C-ring. The products can be used as educts for the synthesis of highly oxidized terpene derivatives. Received October 15, 2001. Accepted November 5, 2001     

Flow-Injection Spectrophotometric Determination of Diclofenac or Mefenamic Acid in Pharmaceuticals

 Two flow injection (FI) spectrophotometric methods are proposed for the determination of diclofenac (DCF) or mefenamic acid (MF) in bulk samples and pharmaceuticals. Both methods are based on the reaction of DCF or MF with potassium ferricyanide in a sodium hydroxide medium. The absorbance of the orange products obtained is measured at 455 nm for DCF and 465 nm for MF. The corresponding calibration graphs are linear over the range 0.20–20.0 mg L⁻¹ for DCF and 1.00–100 mg L⁻¹ for MF, while the limits of detection were 0.05 and 0.18 mg L⁻¹, respectively. Received March 27, 2000. Revision November 15, 2000.     

Reaction of N-Acyl-α-triphenylphosphonio-α-amino Acid Esters with Organic Bases: Mechanism of the Base-Catalyzed Nucleophilic Substitution of the Triphenylphosphonium Group

Summary.  Reactions of N-acyl-α-triphenylphosphonio-α-amino acid methyl esters with organic bases (triethylamine or DBU) were investigated as the crucial step of the base-catalyzed displacement of the triphenylphosphonium group by nucleophiles. It was proved that N-acyl-α-triphenylphosphonioglycinates are transformed to an equilibrium mixture of the corresponding N-acyliminoacetates and N-acyl-α-triphenylphosphoranylidene glycinates by bases. In the case of N-acyl-α-triphenylphosphonio-α-amino acid esters with quaternary α-carbon, the α-substituted homologues of the N-acyliminoacetates were detected to be the only primary reaction product which, however, can undergo further tautomerization to the corresponding α,β-dehydro-α-amino acid derivatives. In both these cases the reaction of N-acyl-α-triphenylphosphonio-α-amino acid esters with nucleophiles proceeds via the addition of a nucleophile to the activated C=N double bond of the N-acylimino intermediate. Corresponding author. E-mail: romanm@zeus.polsl.gliwice.pl Received October 31, 2001. Accepted (revised) December 17, 2001     

Coordination Chemistry of Lipoic Acid and Related Compounds V [1]. New Heteroditopic Ligands Derived from Monoazacrown Ethers and Lipoic Acid

Summary.  Lipoyl imidazolide reacts with aza-15-crown-5 (1,4,7,10-tetraoxa-13-azacyclopentadecane) or aza-18-crown-6 (1,4,7,10,13-pentaoxa-16-azacyclooctadecane) to afford new N-lipoylated azacrown compounds in good yields. These compounds can be transformed into 1,3-dithiols and amines by reduction with complex hydrides of the disulfide and/or amide group of the lipoyl chain. The new pendant-arm macrocycles react as heteroditopic ligands by forming dithiolate and disulfide complexes with the ‘soft’ metal ions Ni²⁺ and Pd²⁺, respectively, and an amine complex with the ‘hard’ Li⁺ ion. Semiempirical and DFT calculations on the complexation of a lithium ion give a most favourable structure in which the azacrown and two solvent molecules are in contact with the metal but not the pendant arm. Received January 29, 2002; accepted (revised) March 25, 2002     

The Products of Vicarious Nucleophilic Substitution and Annelation in the Reactions of α-Haloalkyl Carbanions with Benzonaphthyridines and their N-Oxides

Summary.  Carbanions of chloromethyl 4-tolylsulfone, bromo- and chloromethanesulfomorpholide, and neopentyl chloromethanesulfonate react with benzonaphthyridines and their N-oxides via two pathways: vicarious nucleophilic substitution of hydrogen and annelation. The results are rationalized in terms of the negative charge delocalization in the intermediate σ-adducts. Received October 15, 2001. Accepted (revised) November 26, 2001     

Vicarious Nucleophilic Substitution of Hydrogen and Formation of Aziridine Rings in Reactions of Benzonaphthyridines and their N-Oxides with Chloromethyl Phenyl Sulfone

Summary.  Treatment of benzonaphthyridines with chloromethyl phenyl sulfone in the presence of base led to the formation of aziridine rings annelated to the benzonaphthyridine skeleton, whereas their N-oxides underwent vicarious nucleophilic substitution of hydrogen (VNS), thus leading to the corresponding phenylsulfonylmethyl derivatives. Received December 11, 2000. Accepted (revised) January 22, 2001     

Beauveria bassiana ATCC 7159 Containsan L-Specific a-Amino Acid Benzamidase

Summary.  Biotransformation of a series of racemic N-benzoyl α-amino acids by the fungus Beauveria bassiana ATCC 7159 results in isolation of the corresponding D-amino acid benzamides in high enantiomeric purity and yield. Received December 20, 1999. Accepted January 21, 2000     

Vanadophosphoric Acid as a Modified Reagent for the Spectrophotometric Determination of Certain Cephalosporins and their Dosage Forms

Summary.  Vanadophosphoric acid in acidic medium is proposed as a modified reagent for the spectrophotometric determination of cephalexin, cephaprine sodium, cefazolin sodium, and cefotaxime in pure samples and in pharmaceutical preparations. The method is based on acid hydrolysis of cephalosporins and subsequent oxidation with vanadophosphoric acid. The resulting solution exhibits maximum absorption at about 516 nm. The effects of reaction conditions were investigated. Lambert-Beer’s law was obeyed over a concentration range of about 0.4–45 μg · cm⁻³. For more accurate results, Ringbom optimum concentration ranges were obtained, and the molar absorptivities and Sandell sensitivities were derived. The proposed method was applied to the determination of the drugs in pharmaceutical formulations; the results demonstrated that the proposed method is as accurate, pecise, and reproducible as the official methods. Received August 13, 1999. Accepted (revised) December 7, 1999     

Determination of Acetic Acid in Vinegar by Gas Phase Molecular Absorption Spectrometry After Methyl Acetate Generation

 This paper describes a method for the quantitative determination of acetic acid by gas-phase molecular absorption spectrometry. The proposed method is based on the generation of methyl acetate with subsequent measureme nt of the volatile absorbance at 216 nm. The generation, transport and measurement conditions are optimized. Under the recommended conditions, the analytical characteristics are obtained, with a detection limit of 0.005 M. The method is tested with vinegar samples. The analytical results obtained by the proposed method agree with those of a reference method. Received October 27, 1999. Revision February 5, 2000.     

Solution Structure of Mesobiliverdin XIIIα Bridged Between the Propionic Acid Substituents [1]

Summary.  The solution structure of two intramolecular diesters (methylene and 1,3-propylidene) of mesobiliverdin-XIIIα was studied and compared with that of the corresponding dimethyl ester. The UV/Vis absorption spectra, chiral discrimination with ethyl (S)-(−)-lactate, and the ¹H NMR spectra (ROESY) show that the cyclization of the propionate substituents of biliverdins does not significantly affect the helix structure or its (P) ⇌ (M) interconversion. The internal methylene diester does not show conformational heterogeneity of the propionate substituents and probably exists only in one diastereomeric form. In this case, the results point to a simultaneous racemization of the tetrapyrrole helix and the bridge cycle. The methylene diester of mesoprotoporphyrin was also synthesized. In this case, the geometry of the propionate chains is probably similar to that present in some hemoproteins. Received November 27, 1997. Accepted December 3, 1997     

Cetyldimethylethylammonium-Selective PVC Electrode Basedon its Ion-Associate with Phosphotungstic Acid

 A PVC membrane electrode selective for cetyldimethylethylammonium (CDEA) ion was prepared. The active element is a plasticized poly vinyl chloride membrane containing a dissolved ion associate complex of CDEA with phosphotungstic acid (PTA). The electrode showed a near-Nernstian response within the CDEA⁺ concentration range 2.34 × 10⁻⁶ to 1.96 × 10⁻⁴ M at 25 ± 1^{^}C, good selectivity, and is usable within the pH range 3.5–9.0. The isothermal temperature coefficient of the electrode amounted to −0.00012 V/°C. The electrode has been used for the direct determination of cetyldimethylethylammonium bromide either by the standard addition method or by potentiometric titration against PTA. Received January 1, 1998. Revision June 13, 2000.     

Preparation, Structure, and Thermal Decomposition of Co(II) Complexeswith 2,3- and 2,5-Dichlorobenzoic Acid and Imidazole

Summary.  The reaction products of Co(II)-2,3- and -2,5-dichlorobenzoate with imidazole (1, 2; CoL ₂⋯2imdċ2H₂O, L=C₇H₃Cl₂O, imd=imidazole) were characterized by their spectroscopic and thermochemical properties. The compounds crystallize in the monoclonic system with space group = P2₁/c, a=13.848(3), b=12.841(3) ?, c= 7.064(2) ?, β=98.12 °, V=1243.5(4) ?³, Z=2 for 1 and space group =P2₁/n, a=13.293(3), b= 6.964(2), c=13.800(3) ?, β=108.92(3) °, V=1208.6(4) ?³, Z=2 for 2. The complexes lose their crystal water in one step at 333 K and subsequently decompose to CoO with intermediate formation of Co₃O₄. Received August 9, 1999. Accepted (revised) February 11, 2000     

A Mild Deoxygenation of Heteroaromatic N-Oxides by Formamidinesulfinic Acid

Summary.  Various heteroaromatic N-oxides were efficiently deoxygenated to the corresponding bases under mild conditions using formamidinesulfinic acid (thiourea S,S-dioxide). Received March 24, 2000. Accepted April 18, 2000