A structure-activity relationship study on multi-heterocyclic molecules: two linked thiazoles are required for cytotoxic activity

Abstract

We report the synthesis, cytotoxicity, and phenotypic analysis of oxazole and thiazole containing fragments. Evaluating the optimal size and heterocycle for growth inhibition and apoptosis showed that activity required at least two thiazoles sequentially connected. This is the first detailed comparison of biological activity between multi-heterocyclic containing fragments.

Figure 1

Three approved drugs: Azaepothilone B, Ritonavir and bleomycin) and one expected to enter phase I testing (Telomestatin) that contain oxazoles and thiazoles

Figure 2

Truncated heterocyclefragment of Ustat A.

Figure 3

Evolution of heterocyclic moieties

Figure 4

Growth inhibition of compounds at 40 μM. Percentage growth inhibition of treated HCT-116 cells was measured using a CCK8 assay. Data represents results for compounds 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10 each at 40uM concentration. Data is from 3 separate experiments performed in quadruplicate and the error bars are the standard errors of the mean (SEM).

Figure 5

Visualization of HCT-116 cells treated with DMSO (24 hr; 1%), 5 (24 hr; 10 μM) or 9 (24 hr; 10 μM). Nuclei are stained with Hoechst 33342 dye and visualized with a 100X objective. White arrows indicate chromosome condensation (pyknosis).

Scheme 1

Synthesis of trioxazole-thiazole fragment (4) Conditions: a) TMSCH₂N₂, Benzene/MeOH (3:1), 98%; b) Ser(Bzl)-OMe, TBTU, iPr₂NEt, CH₂Cl₂, 2 steps yield: 90% for 1, 95% for 2, and 92% for 3; c) H₂, Pd/C, EtOH; d) DAST, CH₂Cl₂ / K₂CO₃; e) DBU, BrCCl₃, CH₂Cl₂, 3 steps yield: 85% for 1 and 2, 70% for 3; f) LiOH, MeOH; g) NH₄OH, MeOH, ultrasound; h) Lawesson’s reagent, DME, 55%, 2 steps; i) Bromoketo Phenyloxazole, KHCO₃, DME; j) TFAA, pyridine, DME, 72%, 2 steps

Scheme 2

Synthesis of dioxazole-dithiazole fragment (6) Conditions: a) NH₄OH, MeOH, ultrasound; b) Lawesson’s reagent, DME, 2 steps yield: 77% for 5, 70% for 6; c) BrCH₂COCO₂Et, KHCO₃, DME; d) TFAA, pyridine, DME, 2 steps yield: 77% for 5, 69% for 6; e) Bromoketo Phenyloxazole, KHCO₃, DME

Scheme 3

Synthesis of tetrathiazole fragment (10) Conditions: a) TMSCH₂N_2l Benzene/MeOH (3:1); b) NH₄OH, MeOH, ultrasound; c) Lawesson’s reagent, DME, 2 steps yield: 60% for 7, 53% for 8, 73% for 9 and 73% for 10; d) BrCH₂COCO₂Et, KHCO₃, DME; e) TFAA, pyridine, DME, 2 steps yield: 78% for 7, 88% for 10; f) NaOEt, EtOH, 3 steps yield: 97% for 8, 87% for 9; g) Bromoketo Phenyloxazole, KHCO₃, DME