3-Acyl-2,6-diaminopyridines as cyclin-dependent kinase inhibitors: synthesis and biological evaluation RonghuiLin, * YanhuaLu,StevenK.Wetter,PeterJ.Connolly,IgnatiusJ.Turchi, WilliamV.Murray,StuartL.Emanuel,RobertH.Gruninger,AngelR.Fuentes-Pesquera, MaryAdams,NiranjanPandey,SandraMoreno-Mazza, StevenA.MiddletonandLindaK.Jolliffe Johnson & Johnson Pharmaceutical Research & Development L.L.C., Drug Discovery, 1000 Route 202, Raritan, New Jersey 08869, USA Received15February2005;revised4March2005;accepted7March2005 Abstract—Anovelseriesof2,6-diamino-3-acylpyridinesweredesignedandsynthesizedascyclin-dependentkinase(CDK)inhibi- tors.Therepresentativecompounds 2r and 11 showedpotentCDK1andCDK2inhibitoryactivitiesandinhibitedcellularprolif- erationinHeLa,HCT116,andA375tumorcells. Ó 2005 Elsevier Ltd. All rights reserved. Cyclin-dependent kinases (CDKs), such as CDK1, CDK2, and CDK4, constitute a class of serine–threo- nineproteinkinasesthatplaysanimportantroleinregu- lationofthecellcycle. 1 AbnormalCDKcontrolofthe cell cycle has been strongly linked to the molecular pathologyofcancer.CDKshavethusbecomeattractive therapeutictargetsforcancertherapy. 2 TheCDKsregu- latecellcycleprogressionthroughcomplexeswiththeir corresponding cyclin partners such as cyclin A, B, D, andE.Forexample,CDK1associatedwithcyclinBregu- latesthecellcycleattheG2andmitosis(celldivision) phases. CDK1 inhibitors could block mitosis entry andarrestcellgrowth,andthereforemaybeusefulther- apeutic agents with potentially fewer side effects than conventionalcytotoxicdrugstargetingDNAsynthesis. SeveralCDKinhibitorshaveenteredclinicalevaluation forthetreatmentofcancer. 3 Theseincludeflavopiridol, 7-hydroxystaurosporine (UCN-01), roscovitine (CYC202), and an aminothiazole compound (BMS- 387032). 4 In our program to develop CDK inhibitors as anti-cancer agents, we recently discovered that acyl- substituted diaminotriazole derivatives such as RWJ- 387252 (1) are potent and selective CDK inhibitors and anti-proliferative agents. 5 To investigate the role ofthecentralheterocycliccoreinthebiologicalactivity oftheacyl-diaminotriazoles,wedesignedanewseriesof 3-acyl-2,6-diaminopyridines(2)aspotentialCDKinhibi- tors.Hereinwereportthesynthesisofthesenovelcom- pounds and their biological evaluation as inhibitors of CDKactivityandtumorcellproliferation. Synthesis of 3-acyl-N 6 -aryl-2,6-diaminopyridines (2) unsubstitutedatthe4-positionisoutlinedin Scheme1. The key steps involved ortho-metalation–acylation of an N,N-diprotected 2,6-diaminopyridine, followed by nucleophilicsubstitutiononactivatedarylorheteroaryl halides with the less sterically-hindered 6-amino group of the deprotected 3-acyl-2,6-diaminopyridine products (3). Specifically, ortho-metalation–acylation of 2,6-bis- (pivaloylamino)pyridine(4) 6 wasachievedbyfirsttreat- ingwith n-butyllithiumat 78 °Cin tert-butyl methyl ether(MTBE)containing(N,N,N 0 ,N 0 -tetramethyl)ethyl- enediamine (TMEDA), followed by coupling with an acylchloride.Subsequenthydrolysisofthepivaloylpro- tecting groups with aqueous KOH afforded the 3-acyl- 2,6-diaminopyridines(3).Selectivenucleophilicsubstitu- tionofaryliodidesorbromideswiththe6-aminogroup of 3 wasgenerallyperformedunderpalladium-catalyzed conditionstogivethedesiredcompounds(2a–b, 2e, 2j–l, and 2y). 0960-894X/$-seefrontmatter Ó 2005ElsevierLtd.Allrightsreserved. doi:10.1016/j.bmcl.2005.03.024 Keywords: Synthesis; Cyclin-dependent kinase inhibitor; CDK inhibi- tor;Cellproliferationinhibitor. * Corresponding author. Tel.: +1 908 704 5268; fax: +1 908 526 6465;e-mail: rlin@prdus.jnj.com Bioorganic&MedicinalChemistryLetters15(2005)2221–2224