Synthesis and Biological Activity Assessment of 2-Styrylbenzothiazoles as Potential Multifunctional Therapeutic Agents

Abstract

A current trend in healthcare research is to discover multifunctional compounds, able to interact with multiple biological targets, in order to simplify multi-drug therapies and improve patient compliance. The aim of this work was to outline the growing demand for innovative multifunctional compounds, achieved through the synthesis, characterisation and SAR evaluation of a series of 2-styrylbenzothiazole derivatives. The six synthesised compounds were studied for their potential as photoprotective, antioxidant, antiproliferative, and anti-inflammatory agents. In order to profile antioxidant activity against various radical species, in vitro DPPH, FRAP and ORAC assays were performed. UV-filtering activity was studied, first in solution and then in formulation (standard O/W sunscreen containing 3% synthesised molecules) before and after irradiation. Compound BZTst6 proved to be photostable, suitable for broad-spectrum criteria, and is an excellent UVA filter. In terms of antioxidant activity, only compound BZTst4 can be considered a promising candidate, due to the potential of the catechol moiety. Both also showed exceptional inhibitory action against the pro-inflammatory enzyme 5-lipoxygenase (LO), with IC₅₀ values in the sub-micromolar range in both activated neutrophils and under cell-free conditions. The results showed that the compounds under investigation are suitable for multifunctional application purposes, underlining the importance of their chemical scaffolding in terms of different biological behaviours.

Keywords: ant-inflammatory; antioxidants; antitumor; benzothiazole derivatives; multifunctional.

Scheme 1

Rational design of 2-styryl-benzothiazoles BZTst1–6.

Scheme 2

Synthetic approach for styril-benzothiazole derivatives BZTst1–6. Reagents and conditions: (a) Ac₂O, 3.5 h, reflux; (b) Ar-CHO, Ac₂O (cat.), 120 °C, 16–18 h; (c) HCl 6N, MeOH, 24 h, rt.

Figure 1

Overlaid absorbance spectra of styryl-benzothiazoles BZTst1–6. Light blue (BZTst1), violet (BZTst2), red (BZTst3), teal (BZTst4), brown (BZTst5), light brown (BZTst6).

Figure 2

Modulation of LM formation in primary human monocytes pre-treated with vehicle (DMSO), compounds BZTst1–6 (10 µM) or diclofenac (1 µM) for 10 min prior to stimulation with A23187 (2.5 µM) for 30 min. (A) Schematic of LM biosynthetic pathways and resulting levels of (B) AA, (C) PGE₂, (D) LTB₄, (E) 5-HETE, and (F) 12-HETE. Mean ± SD of three independent experiments. * p < 0.05; ** p < 0.01 *** p < 0.001; **** p ≤ 0.0001 (one-way ANOVA followed by Dunnett’s multiple comparison test, with a single pooled variance).

Figure 3

Modulation of 5-LO activity by compounds BZTst2, BZTst4, and BZTst6 in a cell-free (isolated enzyme; red) and cell-based (primary human PMNL; blue) model. The isolated 5-LO enzyme or PMNL was pre-incubated with the indicated concentrations of compounds BZTst2, BZTst4, and BZTst6 or vehicle for 10 min prior to stimulation with CaCl₂ (2 mM) and AA (20 µM) (cell-free) or A23187 (2.5 µM) (cell-based) for 10 min.

Figure 4

ROS production (% of control) in PMNL treated with vehicle (DMSO), compounds BZTst1–6 (10 µM) or DPI (10 µM) prior to stimulation with PMA (10 µM). Mean ± SD of three independent experiments. * p < 0.05; ** p < 0.01 *** p < 0.001; **** p ≤ 0.0001 (one-way ANOVA followed by Dunnett’s multiple comparison test, with a single pooled variance).