Structure-activity relationship study of bone morphogenetic protein (BMP) signaling inhibitors

Abstract

A structure-activity relationship study of dorsomorphin, a previously identified inhibitor of SMAD 1/5/8 phosphorylation by bone morphogenetic protein (BMP) type 1 receptors ALK2, 3, and 6, revealed that increased inhibitory activity could be accomplished by replacing the pendent 4-pyridine ring with 4-quinoline. The activity contributions of various nitrogen atoms in the core pyrazolo[1,5-a]pyrimidine ring were also examined by preparing and evaluating pyrrolo[1,2-a]pyrimidine and pyrazolo[1,5-a]pyridine derivatives. In addition, increased mouse liver microsome stability was achieved by replacing the ether substituent on the pendent phenyl ring with piperazine. Finally, an optimized compound 13 (LDN-193189 or DM-3189) demonstrated moderate pharmacokinetic characteristics (e.g., plasma t(1/2)=1.6h) following intraperitoneal administration in mice. These studies provide useful molecular probes for examining the in vivo pharmacology of BMP signaling inhibition.

Figure 1

BMP signaling inhibitor of SMAD 1/5/8 phosphorylation.

Scheme 1

(Method A). Reagents and conditions: (a) (MeO)₂CHNMe₂, Et₃N (for pyridine and quinoline salts), DMF, 110 °C, 4 – 6 h, 100%; (b) NH₂NH₂·HBr, EtOH/H₂O, 110 °C, 6 h, 45 – 80%; (c) ArCH(CHO)₂, AcOH, EtOH, 110 °C, 6 h (or MW, 170 °C, 5 min); (d) ArB(OH)₂, Pd₂(dba)₃, 2-dicyclohexylphosphino-2′,4′,6′-triisopropylbiphenyl, K₃PO₄, n-BuOH, MW, 150 °C, 8 min, 84 – 90%; (e) HBr/HOAc, MW, 130 °C, 8 min, 65 – 86%; (f) R₂N(CH₂)_nCl·HCl, Cs₂CO₃, NaI (cat), DMF, 60 °C, 3 h, (or MW, 140 °C, 6 min), 30 – 75% or Cl(CH₂)_nCl, K₂CO₃, DMF, MW, 140 °C, 6 min, then R₂NH, NaI (cat), DMF, MW, 150 °C, 10 min, 30 – 60%.

Scheme 2

(Method B). (a) (MeO)₂CHNMe₂, 110 °C, 16 h, 100%; (b) NH₂NH₂·HBr, EtOH/H₂O, 110 °C, 4 h, 80%; (c) 4-BrPhCH(CHO)₂, AcOH, EtOH, MW, 170 °C, 5 min, 54%; (d) N-Cbz-piperazine, Pd₂(dba)₃, (2-biphenylyl)di-tert-butylphosphine, KOBu-t, DME, 100 °C, 20 h, 20 – 30%; (e) H₂ (1 atm), 5% Pd/C (57% H₂O), MeOH/CH₂Cl₂, rt, 4h, 86%.

Scheme 3

(Method C). (a) BrCH(CHO)₂ (or 4-OMePhCH(CHO)₂ for 15b) AcOH, EtOH, 80 °C, 7 h, 49%; (b) B(O[C(CH₃)₂]₂O)-4-Ph-N-Boc-piperazine, Pd(PPh₃)4, K₂CO₃, dioxane/H₂O, MW, 150 °C, 8 min, 90% (or 110 °C, 3 h, 86%); (c) NBS, CH₂Cl₂, rt, 5 h, 79%; (d) quinoline-4-boronic acid, Pd₂(dba)₃, 2-dicyclohexylphosphino-2′,4′,6′-triisopropylbiphenyl, K₃PO₄, n-BuOH, MW, 150 °C, 15 min, 46%; (e) 4 N HCl in 1,4-dioxane, MeOH, rt, 24 h, 95%; (f) HBr/HOAc, MW, 130 °C, 8 min, 81%; (g) Cl(CH₂)₂Cl, K₂CO₃, DMF, MW, 140 °C, 6 min, then N-Me-piperizine, NaI (cat), DMF, MW 150 °C, 10 min, 57%.

Scheme 4

(Method D). (a) Br₂, CHCl₃, 0 °C, 57%; (b) HNO₃ (70%), Ac₂O, −40 °C to rt, 40 %; (c) NaOMe, MeOH, rt, 99%; (d) quinoline-4-boronic acid, Pd(PPh₃)₄, Na₂CO₃, 1,4-dioxane, reflux, 16 h, 60 %; (e) H₂ (1 atm), 10% Pd/C, MeOH, rt, 0.5 h; (f) 4-MeOPhCH(CHO)₂, AcOH, EtOH, reflux, 16 h, 73 %; (g) 40% aqueous H₂SO₄, 110 °C, 2 h, 91 %; (h) 40% aqueous H₂SO₄, 110 °C, 2 days, 71 %; (i) piperidyl-NCH₂CH₂Cl·HCl, 60 % NaH, DMF, rt, 24 h, 80 %.

Scheme 5

(Method E). (a) 4-MeOPhB(OH)₂, Pd(PPh₃)₄, K₃PO₄, 1,4-dioxane, 100 °C, 18 h, 58%; (b) 2,4-di-NO₂PhONH₂, CH₃CN, 40 °C, 20 h; (c) HC≡CCO₂Me, K₂CO₃, DMF, rt, 33 – 37% over two steps (32a:32b and 33a:33b ~ 1:2); (d) B(O[C(CH₃)₂]₂O)-4-Ph-N-Boc-piperazine, Pd(PPh₃)₄, K₂CO₃, 1,4-dioxane/H₂O, 110 °C, 5 h, 73%; (e) NaOH, EtOH/H₂O (6:1), Δ, 3 h; (f) 4-bromoquinoline, Pd(acac)₂, CuI, K₂CO₃, 1,10-phenanthroline, 4Å MS, NMP, 165 °C, 24 h, 10 – 22% (over two steps); (g) 4N HCl in 1,4-dioxane, MeOH, rt, 24 h.