NMR studies of 4(3H)-quinazolinones and 4(3H)-quinazolinethiones

Summary Unambiguous¹H and¹³C NMR assignments for 4(3H)-quinazolinones1–6 and their corresponding 4-thiones7–12 have been made. This resulted in the revision of the previous assignments for the two benzenoid carbons (C-5 and C-8) of quinazolinones1,2,4, and5. Thionation of the nucleophilic amides1–6 has been found to cause a distinct change in the¹³C chemical shift of particularly C-4, but also of those of C-4a, C-5, and C-8a. One-bond and several long range heteronuclear coupling constants for the compounds have also been measured.

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Kernresonanzspektroskopie von 4(3H)-Chinazolinonen und 4(3H)-Chinazolinthionen

Zusammenfassung Die¹H- und¹³C-NMR-Spektren der 4(3H)-Chinazolinone1–6 und ihrer entsprechenden 4-Thione7–12 wurden zugeordnet. Dabei zeigte sich, daß eine frühere Zuordnung der beiden benzoiden Kohlenstoffe (C-5 und C-8) der Chinazolinone1,2,4 und5 falsch war. Ersatz des Sauerstoffs durch Schwefel in den nukleophilen Amiden1–6 führt insbesondere für C-4, aber auch für C-4a, C-5 und C-8a zu einer deutlichen Änderung der chemischen Verschiebung. Heteronukleare Kopplungskonstanten über eine und über mehrere Bindungen wurden bestimmt.

     

An expedient, regioselective synthesis of 2-alkylamino- and 2-alkylthiothiazolo[5,4-e]indoles

1-Benzenesulfonyl-5-aminoindole 5, prepared from 5-nitroindole 3, was condensed with alkyl isothiocyanates and separately with carbon disulfide and alkyl bromides/iodides to furnish efficiently the corresponding N-alkyl-thioureidoindoles 6a-c and the alkyl N-(indol-5′-yl)dithiocarbamates 9a-e, respectively. Their cyclisation using N-bromosuccinimide (NBS) and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), in the cold, followed by indolic N-deprotection, furnished regioselectively the 2-alkylamino- and the 2-alkylthiothiazolo[5,4-e]indoles 8a-c and 11a-e, respectively, in good overall yields.     

Spectrophotometr1c determination of palladium : Bismuthiol i as an analytical reagent

The reagent, bismuthiol l, has been successfully utilized for the spectrophotometric determination of palladium. The colour reaction is instantaneous and the system is stable for at least 24 hours in the pH range 6 to 10 but shows no sharp peak of maximum absorption. The system obeys Beer's law at a palladium concentration of 0.8 μg to 8.0 μg per ml at any wavelength between 400 mμ and and 410 mμ giving a sensitivity of 0.08 μg of palladium per cm² (practical); 0.01 μg of palladium per cm² (sandell). Ethyl alcohol stabilizes the system against any deviation due to appearance of turbidity. A large excess of the reagent and almost all thc cations and anions, except platinum, gold, copper, chromium, iron, mercury, silver, thallium, uranium, vanadate and cyanide, do not interfere. By applying job's method of continuous variation it was found that the complex contains thc reactants in 1 : 1 ratio and that the average value of the dissociation constant of the complex is 3.2$\text{.}\text{?}$ 10^-5 at 25°.     

An Expedient Synthesis of 5,11-Dimethylindolo[3,2-b]-carbazole,A Potent Ligand for the Receptor for TCDD

A new and efficient synthesis has been developed for the title indolocarbazole which has been indicated by a recent computer-aided study to be a potent ligand for the receptor for the naturally occurring carcinogen, TCDD.     

One Pot One Step Photoconversion of Pulvinic Acid Dilactone to p-Methoxyvulpinic Acid

The utility of singlet oxygen-methanol as a reagent for nuclear methoxylation of complex organic natural products is illustrated by a one pot one step photoconversion of pulvinic acid dilactone to p-methoxyvulpinic acid. The study is important from biogenetic considerations.     

Modeling Thioredoxin Reductase-Like Activity with Cyclic Selenenyl Sulfides: Participation of an NH⋅⋅⋅Se Hydrogen Bond through Stabilization of the Mixed Se−S Intermediate

At the redox-active center of thioredoxin reductase (TrxR), a selenenyl sulfide (Se−S) bond is formed between Cys497 and Sec498, which is activated into the thiolselenolate state ([SH,Se⁻]) by reacting with a nearby dithiol motif ([SH^Cys59,SH^Cys64]) present in the other subunit. This process is achieved through two reversible steps: an attack of a cysteinyl thiol of Cys59 at the Se atom of the Se−S bond and a subsequent attack of a remaining thiol at the S atom of the generated mixed Se−S intermediate. However, it is not clear how the kinetically unfavorable second step progresses smoothly in the catalytic cycle. A model study that used synthetic selenenyl sulfides, which mimic the active site structure of human TrxR comprising Cys497, Sec498, and His472, suggested that His472 can play a key role by forming a hydrogen bond with the Se atom of the mixed Se−S intermediate to facilitate the second step. In addition, the selenenyl sulfides exhibited a defensive ability against H₂O₂-induced oxidative stress in cultured cells, which suggests the possibility for medicinal applications to control the redox balance in cells.     

Urea oxidation electrocatalysis on nickel hydroxide: the role of disorder

Journal of Solid State Electrochemistry - The urea oxidation reaction (UOR) is an important challenge in electrocatalysis, in the context of electrolyzers, fuel cells, medical sensing, and...     

Recognition of anions and monocarboxylic acids by a fluorescent guanidine-based receptor

A guanidine-based fluorescent receptor has been synthesised to study its binding behaviour towards anions (F^? , Cl^? , Br^? , I^?  and AcO^? ). The two donor N–H bonds of the receptor do not point in the same direction; rather, one N–H bond is intramolecularly hydrogen-bonded with the carbonyl oxygen atom. The nature of the donor–acceptor (DA) arrangement induces moderate binding properties. The binding behaviour towards monocarboxylic acids (benzoic acid and phenylacetic acid) is also compared. The binding behaviour of receptor 1 towards the F^?  anion is higher among the anions studied, whereas in the case of monocarboxylic acid, the binding constant with phenylacetic acid is higher than benzoic acid.