Geonir M. Siqueira

Regiospecific acylation of acetals. A convenient method to obtain β-methoxyvinyl trichloromethyl ketones

Abstract The regiochemistry of the acylation of enol ethers, generated in situ, from acetals of unsymmetrical ketones is reported. These results demonstrate a convenient one-pot method to obtain a series of β-methoxyvinyl trichloromethyl ketones [CCl 3 COCHC(OMe)R, where R=Et, n -Bu, i -Pr, (CH 2 ) 2 C(OMe)CHC(O)CCl 3 and (CH 2 ) 5 CO 2 CH 3 )] in high yields.

Ultrasound promoted synthesis of thioesters from 2-mercaptobenzoxa(thia)zoles

An ultrasound-enhanced method has been developed for the synthesis of a variety of thioesters from benzoyl chlorides and 2-mercaptobenzoxa(thia)zoles. Applying this methodology, 14 compounds were synthesized in excellent yields.

Ultrasound-promoted synthesis of 3-trichloromethyl-5-alkyl(aryl)-1,2,4-oxadiazoles

The alternative synthesis of 12 1,2,4-oxadiazoles using ultrasound irradiation from trichloroacetoamidoxime and acyl chlorides is reported. Seven of them are novel compounds. The 3-trichloromethyl-5alkyl(aryl)-1,2,4-oxadiazoles have been synthesised in better yields and shorter reaction times compared to the conventional method. This protocol can be applicable for preparation of 1,2,4-oxadiazoles containing aryl or alkyl groups attached at their C-5 side-chain.

Ultrasonics promoted synthesis of thiazolidinones from 2-aminopyridine and 2-picolilamine

The efficient multicomponent synthesis of thiazolidinones from the reaction of arenealdehydes, mercaptoacetic acid and 2-picolilamine or 2-aminopyridine under ultrasound irradiation are reported. The reaction with 2-aminopyridine needs a Lewis acid catalysis to afford the corresponding 2-aryl-3-(pyridin-2-yl)-1,3-thiazolidin-4-ones. All novel compounds were identified and characterized by (1)H and (13)C NMR spectra. Applying the sonochemical methodology, two series of heterocyclic thiazolidinones were synthesized in good yields after short reaction times.

Antifungal Activity of 3-(heteroaryl-2-ylmethyl)thiazolidinone Derivatives

Thiazolidinones, synthesized from multicomponent reactions of 2-heteroarylmethylamine, arenealdehydes and mercaptoacetic acid, have been tested against six yeasts, namely Candida albicans, C. parapsilosis, C. guilliermondii, Cryptococcus laurentii, Trichosporon asahii and Rhodotorula spp. The activities were expressed as minimum inhibitory concentrations (MIC) and the minimum fungicidal concentrations (MFC). The most affected yeasts were Rhodotorula spp and T. asahii. The cytotoxicities of the thiazolidinones against the fibroblast 3T3/NIH cell line are also described. The antifungal results and the low cytotoxicity of the compounds in this work provide good guides for the further development of active compounds.

7-chloroquinolin-4-yl arylhydrazone derivatives: synthesis and antifungal activity.

Fifteen 7-chloro-4-arylhydrazonequinolines have been evaluated for their in vitro antifungal activity against eight oral fungi: Candida albicans, C. parapsilosis, C. lipolytica, C. tropicalis, C. famata, C. glabrata, Rhodutorula mucilaginosa, and R. glutinis. Several compounds exhibited minimum inhibitory concentration (MIC) and minimum fungicidal concentration (MFC) activities comparable with the first-line drug fluconazole. These results could be considered as an important starting point for the rational design of new antifungal agents.

Efficient Synthesis and Antioxidant Evaluation of 2-Aryl-3-(Pyrimidin-2-yl)-Thiazolidinones

In the present study, we reported the efficient synthesis of 11 3‐(pyrimidin‐2‐yl)‐thiazolidinones in good yields using molecular sieve as the desiccant agent. In addition, we have evaluated the antioxidant capacity of the synthesized compounds by the 2,2‐diphenyl‐2‐picrylhydrazyl hydrate (DPPH•) and the 2,2‐azinobis(3‐ethylbenzothiazoline‐6‐sulfonic acid) diammonium salt (ABTS+•) radicals scavenging assay. Six compounds showed antioxidant activity towards DPPH• (EC50 between 16.13 and 49.94 µg/mL) and also demonstrated excellent activity regarding ABTS+• (TEAC: 10.32–53.52). These results showed that compounds 3‐(pyrimidin‐2‐yl)‐thiazolidinones may be easily synthesized by a less expensive procedure and could be a good starting point to the development of new antioxidant compounds.

Sonochemistry: A good, fast and clean method to promote the synthesis of 5-arylidene-2,4-thiazolidinediones

The efficient synthesis of sixteen 5-arylidene-2,4-thiazolidinediones by aldol condensation reaction of 2,4-thiazolidinedione, mono- and di-substituted arenealdehydes and KOH using ultrasound irradiation is reported. The desired compounds were obtained in a few min (10-30 min) with moderate to good yields (25-81%).

3,4-(Methylenedioxy)aniline as precursor to the synthesis of thiazolidin-4-ones

New 2-aryl-3-(benzo[d][1,3]dioxol-5-yl)thiazolidin-4-ones were easily synthesized by one-pot reaction of (3,4-methylenedioxy)aniline, arenaldehydes (or cyclohexanone), and mercaptoacetic acid which results in good yields. The thiazolidinones were fully identified and characterized by spectroscopic techniques as 1H and 13C NMR, mass and high resolution mass. These novel heterocycles are potential biological compounds due the presence of both important moieties: thiazolidinone and 1,3-benzodioxole.Graphical abstract

The antinociceptive evaluation of 2,3-substituted-1,3-thiazolidin-4-ones through thermal stimulation in mice

The present study assessed the 2,3-substituted-1,3-thiazolidin-4-ones antinociceptive potential looking at the acute nociception model induced by thermal stimulation in mice. This was done to contribute to the development of new analgesic drugs, in addition to the fact that 4-thiazolidinones are an important scaffold associated with many pharmacological activities. The synthesized compounds were characterized by GC-MS and NMR of 1H and 13C and administered at a dose of 100 mg/kg hydrochloride salt (ip). Sodium dipyrone (250 and 500 mg/Kg; ip) and tramadol hydrochloride (25 and 50 mg/Kg; ip) were used as positive controls. The hot plate test was done at a temperature of 50 ± 0.1 °C and animals assessed at 30, 60, and 90 min after the drugs were administered. Among the fourteen compounds tested, nine (5Aa, 5Ab, 5Ac, 5Ad, 5Ba, 5Bb, 5Bd, 5Ea, and 5Fa) showed significant increases in latency time when compared to saline (negative control) and compared to sodium dipyrone (500 mg/Kg; ip) in a 30-min assessment. The highest latency times were obtained for 3-(2-piperidin-1-yl)ethyl)thiazolidin-4-one derivatives (5Ab, 5Ac, and 5Ad). This highlights three findings about the chemical structure that improve activity: (i) an ethylenic link; (ii) a six-membered piperidine; (iii) an aliphatic substituent at the 2-position of thiazolidinone ring.