Efficient solid-phase synthesis of 3-substituted-5-oxo-5H-thiazolo[2,3-b]-quinazoline-8-carboxamides under mild conditions with two diversity positions

Synthesis, Antibacterial, and Antioxidant Evaluation of Novel Series of Condensed Thiazoloquinazoline with Pyrido, Pyrano, and Benzol Moieties as Five- and Six-Membered Heterocycle Derivatives

A novel synthesis of thiazolo[2,3-b]quinazolines 4(a–e), pyrido[2′,3′:4,5]thiazolo[2,3-b]quinazolines {5(a–e), 6(a–e), and 7(a–e)}, pyrano[2′,3′:4,5]thiazolo[2,3-b]quinazolines 8(a–e), and benzo[4,5]thiazolo[2,3-b]quinazoloine9(a–e) derivatives starting from 2-(Bis-methylsulfanyl-methylene)-5,5-dimethyl-cyclohexane-1,3-dione 2 as efficient α,α dioxoketen dithioacetal is reported and the synthetic approaches of these types of compounds will provide an innovative molecular framework to the designing of new active heterocyclic compounds. In our study, we also present optimization of the synthetic method along with a biological evaluation of these newly synthesized compounds as antioxidants and antibacterial agents against the bacterial strains, like S. aureus, E. coli, and P. aeruginosa. Among all the evaluated compounds, it was found that some showed significant antioxidant activity at 10 μg/mL while the others exhibited better antibacterial activity at 100 μg/mL. The results of this study showed that compound 6(c) possessed remarkable antibacterial activity, whereas compound 9(c) exhibited the highest efficacy as an antioxidant. The structures of the new synthetic compounds were elucidated by elemental analysis, IR, ¹H-NMR, and ¹³C-NMR.

Synthesis of thiazolo[2,3-b]quinazoline derivatives via base-promoted cascade bicyclization of o-alkenylphenyl isothiocyanates with propargylamines

A highly efficient cascade bicyclization reaction of o-alkenylphenyl isothiocyanates with propargylamines has been developed, which affords a series of thiazolo[2,3-b]quinazolines in good to excellent yields by using K₂CO₃ as a base in MeCN at 80 °C. This method is transition-metal-free and operationally simple with broad functional group tolerance. Mechanistically, 6-exo-trig hydroamination followed by 5-exo-dig hydrothiolation was involved in this transformation.

Organocatalysis in heterocyclic synthesis: DABCO as a mild and efficient catalytic system for the synthesis of a novel class of quinazoline, thiazolo [3,2-a]quinazoline and thiazolo[2,3-b] quinazoline derivatives

BACKGROUND

There are only limited publications devoted to the synthesis of especially thiazolo[3,2-a]quinazoline which involved reaction of 2-mercaptopropargyl quinazolin-4-one with various aryl iodides catalyzed by Pd-Cu or by condensation of 2-mercapto-4-oxoquinazoline with chloroacetic acid, inspite of this procedure was also reported in the literature to afford the thiazolo [2,3-b] quinazoline. So the multistep synthesis of the thiazolo[3,2-a]- quinazoline suffered from some flaws and in this study we have synthesized a novel class of thiazoloquinazolines by a simple and convenient method involving catalysis by 1,4-diazabicyclo[2.2.2]octane (DABCO).

RESULTS

A new and convenient one-pot synthesis of a novel class of 2-arylidene-2H-thiazolo[3,2-a]quinazoline-1,5-diones 9a-i was established through the reaction between methyl-2-(2-thio-cyanatoacetamido)benzoate (4) and a variety of arylidene malononitriles 8a-i in the presence of DABCO as a mild and efficient catalytic system via a Michael type addition reaction and a mechanism for formation of the products observed is proposed. Moreover 4 was converted to ethyl-2-[(4-oxo-3,4-dihydroquinazolin-2-yl)thio]acetate (10) upon reflux in ethanol containing DABCO as catalyst. The latter was reacted with aromatic aldehydes and dimethylformamide dimethylacetal (DMF-DMA) to afford a mixture of two regioselectively products with identical percentage yield, these two products were identified as thiazolo[3,2-a]quinazoline 9,13 and thiazolo[2,3-b]quinazoline 11,12 derivatives respectively. The structure of the compounds prepared in this study was elucidated by different spectroscopic tools of analyses also the X-ray single crystal technique was employed in this study for structure elucidation, Z/E potential isomerism configuration determination and to determine the regioselectivity of the reactions.

CONCLUSION

A simple and efficient one-pot synthesis of a novel class of 2-arylidene-2H-thiazolo[3,2-a]quinazoline-1,5-diones 9a-i was established through DABCO catalyzed Michael type addition reaction. In addition many fused quinazoline and quinazoline derivatives were synthesized which appeared as valuable precursors in synthetic and medicinal chemistry.

Polymer-supported alpha-acylamino ketones: preparation and application in syntheses of 1,2,4-trisubstituted-1H-imidazoles

Polymer-supported alpha-acylamino ketones were prepared from resin-bound amines, bromoketones, and carboxylic acids. Selective monoalkylation of amines by bromoketones was carried out via 4-nitrobenzenesulfonamides. There was a striking difference in the reaction outcome between 2-Nos and 4-Nos derivatives. Alpha-acylamino ketones were converted to imidazoles. The cyclization was performed on resin, allowing further polymer-supported elaboration of imidazoles including synthesis of bis-heterocyclic compounds. A small combinatorial array of imidazoles was synthesized. Target compounds were prepared under mild conditions using commercially available building blocks for the introduction of three points of diversity.

Efficient traceless solid-phase synthesis of 3,4-dihydropyrazino[1,2-b]indazoles and their 6-oxides

A highly efficient novel traceless solid-phase synthesis of 3,4-dihydropyrazino[1,2-b]indazoles and their 6-oxides was developed by using commercially available building blocks, diamines, 2-nitrobenzenesulfonyl chlorides, and bromoketones/bromoacetates. Mild reaction conditions, diversely substituted building blocks, and high purity of crude products enabled effective combinatorial syntheses of libraries.

Parallel synthesis of an imidazole-4,5-dicarboxamide library bearing amino acid esters and alkanamines

The imidazole-4,5-dicarboxylic acid scaffold is readily derivatized with amino acid esters and alkanamines to afford compounds with intramolecularly hydrogen bonded conformations that mimic substituted purines and therefore are hypothesized to be potential inhibitors of kinases through competitive binding to the ATP site. In this work, a total of 126 dissymmetrically disubstituted imidazole-4,5-dicarboxamides with amino acid ester and alkanamide substituents were prepared by parallel synthesis. The library members were purified by column chromatography on silica gel and the purified compounds characterized by LC-MS with LC detection at 214 nm. A selection of the final compounds was also analyzed by (1)H-NMR spectroscopy. The analytically pure final products have been submitted to the Molecular Library Small Molecule Repository (MLSMR) for screening in the Molecular Library Screening Center Network (MLSCN) as part of the NIH Roadmap.