The first low microM SecA inhibitors

Abstract

SecA ATPase is a critical member of the Sec family, which is important in the translocation of membrane and secreted polypeptides/proteins in bacteria. Small molecule inhibitors can be very useful research tools as well as leads for future antimicrobial agent development. Based on previous virtual screening work, we optimized the structures of two hit compounds and obtained SecA ATPase inhibitors with IC(50) in the single digit micromolar range. These represent the first low micromolar synthetic inhibitors of bacterial SecA and will be very useful for mechanistic studies.

Figure 1

Two hit compounds and their derivatives

Figure 2

Inhibitory effect of compounds 1 and 7a–n at 100 µM against EcN68 Sec A.

Figure 3

Inhibitory effect of compounds 16a–i at 30 µM against EcN68 Sec A.

Figure 4

Inhibitory effect of compounds 16c–e, g–i at 5 µM against EcN68 Sec A.

Figure 5

Inhibitory effect of compounds 17d, e, g–i at 30 µM against EcN68 Sec A.

Figure 6

The inhibitory curves of the two most potent compounds, 16g and 16h, against EcN68 Sec A.

Figure 7

The inhibitory curves of 16g,h and 17h against EcSecA.

Figure 8

The inhibitory curves of 16g,h and 17h against EcSecA.

Figure 9

(A) The proposed docking conformation of HTS-12302 (white sticks) and compound 16g (green sticks) around SecA ATP-site; (B) The proposed schematic interactions of HTS-12302 with SecA; (C) The proposed schematic interactions of compound 16g with SecA

Scheme 1

Synthesis of isoxazole carboxamides 7a–n. Reagents and conditions: (a) HONH₂·HCl, NaOH, EtOH, H₂O, reflux; (b) NCS, DMF; (c) Ethyl acetoacetate, MeONa, THF; (d) NaOH, EtOH, H₂O; (e) EDCI, HOBt, DMAP, DMF

Scheme 2

Synthesis of compounds 11a–g and 14a–i. Reagents and conditions: (a) EtOH, reflux; (b) piperidine, EtOH, reflux

Scheme 3

Synthesis of compounds 15a–g, 16a–i and 17d,e,g–i. Reagents and conditions: (a) K₂CO₃, CH₃CN, reflux