Novel Thiazole-Fused [4,5- g] or [5,4- g]Quinazolin-8-ones and Their Quinazoline Analogues: Synthesis and Biological Evaluation

Abstract

Background/Objectives: In connection with previous work on V-shaped polycyclic thiazolo[5,4-f]quinazolin-9-one and [5,4-f]quinazoline derivatives that can modulate the activity of various kinases, the synthesis of straight thiazole-fused [4,5-g] or [5,4-g]quinazolin-8-ones and quinazoline derivatives hitherto undescribed was envisioned. Methods: An innovative protocol allowed to obtain the target structures. The synthesis of inverted thiazolo[4,5-h] and [5,4-h]quinazolin-8-one derivatives was also explored with the aim of comparing biological results. The compounds obtained were tested against a representative panel of eight mammalian protein kinases of human origin: CDK9/CyclinT, Haspin, Pim-1, GSK-3β, CK-1ε, JAK3, CLK1 and DYRK1A. Results and Conclusions: The results obtained show that the novel linear thiazoloquinazolines are not kinase inhibitors. The cytotoxicity of these newly synthesized compounds was assessed against seven representative tumor cell lines (human cancers: Huh7-D12, Caco-2, HCT-116, MCF-7, MDA-MB-231, MDA-MB-468 and PC-3). The majority of these novel molecules proved capable of inhibiting the growth of the tested cells. The 7-Benzyl-8-oxo-7,8-dihydrothiazolo[5,4-g]quinazolinones 5b and 6b are the most potent, with IC₅₀ values in the micromolar range. None of these compounds showed toxicity against normal cells. A larger program of investigations will be launched to investigate the real potential interest of such compounds in anticancer applications.

Keywords: 4,5-dichloro-1,2,3-dithiazolium chloride; DYRK1A kinase; cytotoxicity; kinase inhibition; microwave-assisted chemistry; thiazoloquinazolines; thiazoloquinazolinones.

Figure 1

Thiazolo[5,4-f]quinazoline (A series) and thiazolo[5,4-f]quinazolin-9(8H)-one (B series) derivatives previously developed in our group.

Figure 2

Straight thiazole-fused [4,5-g] or [5,4-g]quinazolin-8-ones and quinazolines and inverted thiazolo[4,5-h] or [5,4-h]quinazolin-8-one derivatives.

Figure 3

Structures of methyl 8-benzyl-9-oxo-8,9-dihydrothiazolo[5,4-f]quinazoline-2-carbimidate (I) and methyl 9-[(2-fluoro-4-methoxyphenyl)amino]thiazolo[5,4-f]quinazoline-2-carbimidate (II) used as references in this study.

Scheme 1

Retrosynthetic strategy for the synthesis of the novel thiazole-fused quinazolinones.

Scheme 2

Synthesis of aminoquinazolinones 2a, 2b and 2c (isolated yields). Conditions: (a) 1. DMF-DMA (2.5 equiv) in EtOAc (1 M), 70 °C (Mw), 30 min; 2. Benzylamine (1.5 equiv) in AcOH (1 M), 118 °C (Mw), 30 min. (b) Pd/C (10% w/w), HCO₂NH₄ (5.0 equiv) in EtOH (0.2 M), reflux, 1 h.

Scheme 3

Conditions (isolated yields): (a) Appel salt (1.1 equiv), pyridine (2.0 equiv) in CH₂Cl₂ (0.3 M), rt, 1 h; (b) DBU (3.0 equiv) in dry CH₂Cl₂ (0.2 M), rt, 15 min. The ¹H NMR spectra of compounds 4-c show two tautomeric forms in which the thione is the most abundant (ratio major/minor = 90:10; for more details, see the Supplementary Material).

Scheme 4

Synthesis of the regioisomeric thiazole-fused quinazolinones 6a and 6b (isolated yields). Conditions: (a) PdCl₂ (20 mol%), CuI (50 mol%), KI or LiBr (2.0 equiv) in DMSO/DMF 1:1 (0.025 M), air, 120 °C, 4 h. (b) NaOMe (1.0 equiv) in MeOH (0.07 M), 50 °C (Mw), 1 h.

Scheme 5

Conditions (isolated yields): (a) NBS (1.0 equiv), DMF (0.1 M), rt, 2 h. (b) Appel salt (1.1 equiv), pyridine (2.0 equiv) in CH₂Cl₂ (0.3 M), rt, 2 h. (c) CuI (2.0 equiv) in pyridine (0.25 M), 115 °C (Mw), 30 min. (d) NaOMe (1.0 equiv), MeOH (0.07 M), 50 °C (Mw), 1 h.

Scheme 6

Conditions (isolated yields): (a) NBS (1.0 equiv), DMF (0.1 M), rt, 2 h. (b) Appel salt (1.1 equiv), pyridine (2.0 equiv) in CH₂Cl₂ (0.3 M), rt, 2 h. (c) CuI (2.0 equiv) in pyridine (0.25 M), 115 °C (Mw), 30 min. (d) NaOMe (1.0 equiv), MeOH (0.07 M), 50 °C (Mw), 1 h.

Scheme 7

Synthesis of 6- and 7-aminoquinazolines 11a and 11b (isolated yields). Conditions: (a) DMFDMA (0.4 M), EtOAc (1 M), 70 °C (Mw), 30 min. (b) 2-fluoro-4-methyoxyaniline (1.5 equiv), AcOH (1 M), 118 °C (Mw), 30 min. (c) Pd/C (10% w/w), HCO₂NH₄ (5.0 equiv), EtOH (0.2 M), reflux, 1 h.

Scheme 8

Synthesis of cyanothioformamides 13a and 13b (isolated yields). Conditions: (a) In CH₂Cl₂ (0.3 M): 1. Appel salt (1.1 equiv), rt, 1 h; 2. DIPEA (2.0 equiv), rt, 1 h. (b) DBU (3.0 equiv) in dry CH₂Cl₂ (0.2 M), rt, 15 min. Tautomeric ratio major/minor = 90:10 in favor of the thione form (estimated by ¹H NMR).

Scheme 9

Synthesis of the thiazole-fused quinazolines, 15a and 15b, regioisomeric analogues of EHT 1610 (isolated yields). Conditions: (a) PdCl₂ (20 mol%), CuI (50 mol%), KI or LiBr (2.0 equiv), DMSO/DMF 1:1 (0.025 M), air, 120 °C, 4 h. (b) NaOMe (1.0 equiv), MeOH (0.07 M), 50 °C (Mw), 1 h.

Figure 4

Model compounds I and II and the synthesized regioisomers 6a–d, 15a and 15b hitherto undescribed.