Biol 2016, 11, 598C608. containing two em N /em -terminal bromodomains BD1 and BD2) has been an attractive target for treatment of cancers and other diseases.4 Many structurally diverse BET family inhibitors have been reported in recent years.5 Some representative PQM130 molecules highlighted in Figure 1, the I-BET762 (1) and OTX-015 (2, also known as MK-8628) that were structurally similar to the original tool compound JQ1 (3),6 have been evaluated clinically for potential treatment of cancers.7 Most recently, another clinical candidate, structurally distinct BET inhibitor ABBV-075 (4, mivebresib) with high efficacy in Kasumi-1 xenografts was also reported.8 These molecules utilize moieties such as 3,5-dimethyltriazole, 3,5-dimethylisoxazole, and pyrrolo-1-methylpyridin-2-one, which provide critical H-bond interactions with key amino acid residue of bromodomains (e.g. Asn140 in BRD4 (BD1)) and to further inhibit their biological function by interrupting acetylated lysine-bromodomain interactions. Although several compounds have been successfully progressed into the clinic, alternative BET family inhibitors with differentiated core structures, possessing better safety profiles and physicochemical properties remains of high interest. Open in a separate window Figure 1. Representative BET inhibitors and quinazoline-based inhibitors. In our efforts to identify novel BET family inhibitors, the 2-quinolinone analog 5 was developed recently that exhibited good affinity against BRD4 (BD1,2) (BROMOScan Kd = 55 nM) with moderate cellular activity (MV4C11 IC50 = 1.8 M).9 By utilizing 5 as a starting point, we envisioned the bicyclic quinazoline could serve as a structurally distinct template that allows facile functionalization (e.g. at 2-, 4-, 6, and 7-position of quinazoline ring) improving potency and drug-like properties. Herein we report on the initial discovery and optimization of a new chemical series of quinazoline-based BRD4 inhibitors focusing on the lead identification. The synthesis of these quinazoline-based analogs is straightforward and shown in Scheme 1. Replacement of 4-chloro group of commercially available material 7 with the corresponding amine followed by Suzuki coupling of the bromo group with 3,5-dimethylisoxazole-4-boronic ester at lower temperature (e.g. 70 C) gave intermediate 8. Further utilizing the 2-chloro functionality of 8, the desired analogs were obtained by either replacement with amine (e.g. 14C24) or by Suzuki coupling with corresponding boronic acid or ester at 90C95 C (e.g. 25C32). This route is particularly suitable for the investigation of SAR at the 2-position of quinazoline ring. Compound 40 was prepared by the same sequence starting from 2,4-dichloro-7-bromoquinazoline instead. For rapid screening of a potential replacement for the 3,5-dimethylisoxazole moiety, intermediate 9 was PQM130 prepared in a similar manner, which could undergo Suzuki coupling to install various heteroaryl groups at the 6-position (e.g. 41C48). Furthermore, to facilitate the SAR investigation at the 4-position, em t /em -butyl protected intermediate 10 was prepared. The deprotection of PQM130 em t /em -butyl group followed by phosphonium salt activated replacement of hydroxyl group gave desired products 49C54, 56C58, and 60C64.10 Finally, intermediate 12 was prepared by a similar phosphonium salt activated protocol from the tautomerizable substrate 11 followed by Suzuki coupling to install the requisite dimethylisoxazole ring. Hydrolysis and subsequent amide formation using HATU as coupling agent afforded analogs 33C39 containing the 2-substituted amide. Open in a separate window Scheme 1. Reagents and conditions: (a) R1R2NH, Et3N, THF, rt or PQM130 60 C; (b) 3,5-dimethyl-4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)isoxazole, cat. PdCl2(dppf)-CH2Cl2 adduct, K2CO3, 1,4-dioxane/H2O (3/1), 70 C; (c) corresponding amine, ( em i /em -Pr)2NEt, EtOH, 90 C, sealed; or corresponding boronic acid or boronic ester, cat. PdCl2(dppf)-CH2Cl2 adduct, K2CO3, 1,4-dioxane/H2O (3/1), 90C95 C; (d) (3-chlorophenyl)methanamine, Et3N, Rabbit Polyclonal to RGS1 THF, rt, 1 h, 97%; (e) em N /em , em N /em -dimethyl-2-(piperazin-1-yl)ethanamine, ( em i /em -Pr)2NEt, EtOH, 90 C, sealed, 5 h, 95%; (f) corresponding boronic acid or boronic ester, cat. PdCl2(dppf)-CH2Cl2 adduct, K2CO3, 1,4-dioxane/H2O (3/1), 90C95 C; (g) em t /em -BuOK (1 M in.