Ultrasound-assisted green synthesis and antimicrobial assessment of 1,3-thiazoles and 1,3,4-thiadiazines

Abstract

In this article, we applied ultrasonic irradiation as an ecofriendly, green, efficient approach for the synthesis of a new 1,3-thiazoles and 1,3,4-thiadiazines under solvent-free conditions. Thus, thiocarbohydrazide condenses with N-(thiazol-2-yl)acetamide (2) in different molar ratios under ultrasonic irradiation afforded mono and bis thiocarbohydrazons 3a,b, respectively. Thiocarbohydrazones were reacted with α-haloketone, α-haloester as well as hydrazonoyl halides under ultrasonic conditions afforded 1,3-thiazole 4, 1,3-thiazolinone 5 and 1,3,4-thiadiazines 6 and 11a–c, respectively. The reaction of monohydrazone 3a with phthalic anhydride derivatives afforded phthalazines 7a,b in a good yield. Ultrasonic irradiation has benefits such as greater purity, lower cost, high yields, and simple workups compared to the conventional methods. All the new compounds were screened for antimicrobial activity against different tested microbes. Most of the newly synthesized compounds exhibited potent to moderate activities toward the tested microbes. Compounds that exhibited potent antimicrobial activities were selected to measure their MIC and MBC values. The results revealed that compounds 3a, 3b, 8, 10, and 11a showed lower MIC against Staphylococcus aureus with the values of 39.06, 78.13, 9.77, 39.06 and 39.06 µg/ml, respectively. Meanwhile, the MBC values were found to be acceptable for 3a and 10 of 156 and 312, respectively.

Keywords

• ultrasound irradiation
• thiazoles
• hydrazonoyl halides
• thiadiazines
• antimicrobial activity