Chemical synthesis, crystal structure, versatile evaluation of their biological activities and molecular simulations of novel pyrithiobac derivatives

Abstract

Since pyrithiobac (PTB) is a successful commercial herbicide with very low toxicity against mammals, it is worth exploring its derivatives for an extensive study. Herein, a total of 35 novel compounds were chemically synthesized and single crystal of 6-6 was obtained to confirm the molecular structure of this family of compounds. The novel PTB derivatives were fully evaluated against various biological platforms. From the bioassay results, the best AHAS inhibitor 6-22 displayed weaker herbicidal activity but stronger anti-Candida activity than PTB did. For plant pathogenic fungi, 6-26 showed excellent activity at 50 mg/L dosage. Preliminary insecticidal activity and antiviral activity were also observed for some title compounds. Strikingly, 6-5 exhibited a promising inhibitory activity against SARS-CoV M^pro with IC₅₀ of 4.471 μM and a low cellular cytotoxicity against mammalian 293 T cells. Based on the results of molecular modeling, HOMO-1 was considered to be a factor that affects AHAS inhibition and a possible binding mode of 6-5 with SARS-CoV M^pro was predicted. This is the first time that PTB derivatives have been studied as biological agents other than herbicides. The present research hence has suggested that more attentions should be paid to compounds belonging to this family to develop novel agrochemicals or medicines.

Keywords: Acetohydroxyacid synthase; Biological activity; Crystal structure; Pyrithiobac derivative; SARS-CoV M(pro).

Graphical abstract

Fig. 1

Examples of industrial or bioactive thioethers and bioactive compounds containing pyrimidine or triazine ring.

Scheme 1

General synthesis route of intermediate 2 and 3.

Scheme 2

Chemical synthesis route for the target compounds.

Fig. 2

Crystal structure of compound 6–6.

Fig. 3

Inhibition curve of compound 6–5 against SARS-CoV M^pro (Concentration was expressed in nM).

Fig. 4

HOMO-1 orbital maps for compound 6–8, 6–12 and 6–22.

Fig. 5

Possible binding mode of compound 6–5 with SARS-CoV M^pro. (a) A two-dimensional representation by LIGPLOT; (b) Molecular surface of the binding pocket bound with the inhibitor.