Design and synthesis of novel quinone inhibitors targeted to the redox function of apurinic/apyrimidinic endonuclease 1/redox enhancing factor-1 (Ape1/ref-1)

Abstract

The multifunctional enzyme apurinic endonuclease 1/redox enhancing factor 1 (Ape1/ref-1) maintains genetic fidelity through the repair of apurinic sites and regulates transcription through redox-dependent activation of transcription factors. Ape1 can therefore serve as a therapeutic target in either a DNA repair or transcriptional context. Inhibitors of the redox function can be used as either therapeutics or novel tools for separating the two functions for in vitro study. Presently there exist only a few compounds that have been reported to inhibit Ape1 redox activity; here we describe a series of quinones that exhibit micromolar inhibition of the redox function of Ape1. Benzoquinone and naphthoquinone analogues of the Ape1-inhibitor E3330 were designed and synthesized to explore structural effects on redox function and inhibition of cell growth. Most of the naphthoquinones were low micromolar inhibitors of Ape1 redox activity, and the most potent analogues inhibited tumor cell growth with IC(50) values in the 10-20 microM range.

Figure 1

E3330, a reported inhibitor of APE1 redox activity.

Figure 2

Inhibition of Ape1 redox activity measured by electrophoretic mobility shift assay. See experimental section for details.

Scheme 1^a

^aReagents and Conditions: a) H₂O₂, H₂SO₄, MeOH, reflux 3 h; b) K₂CO₃, MeI, acetone, reflux 2 d; c) i. nBuLi, THF, 0 °C, 1 h; ii. MeI, 0 °C, 2 h; d) CHCl₂OCH₃, TiCl₄, CH₂Cl₂, 0 °C to rt 4 h; e) NaH, (EtO)₂P(O)CHRCO₂Et THF, rt 12 h; f) KOH, EtOH, reflux 30 min; g) HNO₃, AcOH, EtOAc, rt 4 h; h) NMFA, POCl₃, CH₂Cl₂, rt 2 d; i) SO₂Cl₂, CH₂Cl₂, rt, 1 h; j) CAN, MeCN, H₂O, 1 h; k) α-bromo-γ-butyrolactone, (EtO)₃P, then NaH, toluene, reflux 8 h; l) H₂SO₄, CH(OCH₃)₃, MeOH, reflux 12 h; m) KOH, EtOH, reflux 30 min.

Scheme 2^a

^aReagents and conditions: a) DCC, ethanolamine, CH₂Cl₂, rt; b) PyBOP, Et₃N, rt 30 min, then ethanolamine, rt 4 h; c) Ag(II)O, HNO₃, AcOH, EtOAc, rt 40 min

Scheme 3^a

^aReagents and conditions: a) i. H₂, 10% Pd/C, THF, rt, 4 h; ii. NaH, Me₂SO₄,2 h, rt; b) R = H, CH₃: TiCl₄, CHCl₂OCH₃, CH₂Cl₂, 0 °C, 4 h; R = OCH₃: i. nBuLi, THF, −78 °C, 3 h; ii. DMF, −78 °C; c) Selectfluor, CH₃CN, reflux; d) SO₂Cl₂, CH₂Cl₂, rt, 4 h; e) Br₂, CH₂Cl₂, rt, 1 h; f) R = H: NaH, (EtO)₂P(O)CHR’CO₂Et, THF, rt, 12 h; R = CH₃, OCH₃, SCH₃, F, Cl, Br: NaH, (EtO)₂P(O)CHR’CO₂Et, PhMe, reflux, 12 h; g) EtOH, KOH, reflux, 1 h; h) R = H, CH₃, OCH_3> SCH₃: HNO₃, EtOAc, AcOH, rt, 3 h; R = F, Cl, Br: HNO₃, EtOAc, AcOH, Ag(II)O, rt, 2 h; i) LiAlH₄, THF, rt, 12 h; j) i. nBuLi, THF, −78 °C; ii. (SCH₃)₂, −78 °C; k) PCC, CH₂Cl₂, rt, 8h

Scheme 4

Scheme 5^a

^aReagents and conditions: a) α-bromobutyrolactone, (EtO)₃P, then NaH, toluene, reflux 8 h; b) H₂SO₄, CH(OCH₃)₃, MeOH, reflux 12 h; c) KOH, EtOH, reflux 30 min; d) R = CH₃: HNO₃, EtOAc, AcOH, rt 3 h; R = Cl or Br: HNO₃, EtOAc, AcOH, Ag(II)O, rt 2 h; e) PyBOP, Et₃N, DMF:CH₂Cl₂ rt 30 min, then ethanolamine, rt 4 h; f) Ag(II)O, HNO₃, AcOH, EtOAc, rt 30 min; g) HBr, CH₂Cl₂; rt 30 min; h) Br₂, CH₂Cl₂, rt 4 h; i) Li(SiMe₃)₂N, CH₃CO₂Et, THF, −78 C to rt 4 h; j) HCl, THF, reflux.