Synthesis and Characterization of Aryl Acylguanidines and Their Copper(Ⅱ) Complexes

A series of eight N-mono-substituted aryl acylguanidines L1~8 were synthesized from the reactions of their parent acylthioureas and respective primary amines, including five R1C(O)N=C(NHR2)2 with balanced arms(denoted as R1–R2–R2: Ph–Ar’–Ar’, L1(1);Ph–Ar’’–Ar’’, L2(2);1-Naph–Ar’–Ar’, L3(3);1-Naph–Ar’’–Ar’’, L4(4);2-Naph–Ar’’–Ar’’, L[5(5);Ar’ = 2,6-Me2C6H3, Ar’’ = 2,6-iPr2C6H3) and three R1C(O)N=C(NHR2)NHR3 with unbalanced arms(denoted as R1–R2–R3: Ph–Ar’–Ph, L6(6);Ph–Ar’ –Ph, L7(7);Ph–Ar’ –Ar’, L8(8)). Treatment of L1~5(1~5) with copper acetate in a molar ratio of 2:1 in dichloromethane led to the formation of homoleptic Cu(Ⅱ) complexes trans-L2n’Cu(9~13), in which the Cu(Ⅱ) center was stabilized by deprotonated ligands Ln’(n = 1~5) in the O,N-bidentate mode. When similar reactions of L6(Ph–Ar’–Ph)(6) and L7(Ph–Ar’’–Ph)(7) that contain unbalanced arms were investigated, the Cu(Ⅱ) products trans-L26’Cu(14) and trans-L27’Cu(15) were formed by deprotonating the bulky amine groups in Ln(-NHAr’ for L6 and-NHAr’’ for L7) rather than the-NHPh group. In sharp contrast, trans-L28’Cu(16) was obtained from two-arm unbalanced L8(Ph–Ar’’–Ar’)(8) not by deprotonating the more bulky-NHAr’’ group but the relatively less bulky-NHAr’ group. In a further exploration, the reaction of 1:1 mixed ligands Ln and Lm with copper acetate was found to give only homoleptic Cu(Ⅱ) complex L2n’Cu instead of the heteroleptic one Ln’CuLm’. The in vitro antibacterial activity of Ln was evaluated against S. aureus, E. coli and C. albicans by determining the minimum inhibitory concentrations(MICs) using Kirby-Bauer test.

Synthesis and Structural Characterization of N,N-disubstituted Acylguanidines

A series of five N,N-disubstituted acylguanidines R1C（O）N=C[N（H）R2]NR23（R1=Mes or Ph; R2=Ar′′or Ar′; R3=Cy, Bn, iPr, or Et）（Mes=2,4,6-Me3C6H2, Ar′′=2,6-iPr2C6H3, Ar′=2,6-Me2C6H3） was synthesized from the reactions of parent acylthioureas with respective secondary amines. According to structutral characterization by single-crystal X-ray diffraction, the rough reduction of the steric hindrance of R substitutents of R1 C（O）N=C[N（H）R2]NR23（also abbreviated as R1-R2-R3 for comparison purposes） led to the slight enlongation of N（1）–C（1） bond lengthes and small decrease of N（1）–C（1）–N（3） bond angles from Mes–Ar′′–Cy（1） to Ph–Ar′′–Bn（2）, Ph–Ar′′–iPr（3） and Ph–Ar′–Cy（4）. At the same time, the N（1）–H（1）···O（1） intramolecular hydrogen bonds were observed in these cases. When R3=Et, an interesting compound Ph-Ar′-Et（5） was obtained with the formation of intermolecular hydrogen bonds instead. 1 belongs to the monoclinic system, space group P2（1/n） with a=9.6488（3）, b=28.5318（8）, c=11.9155（3） A, b=91.439（2）°, V=3279.27（16） A3, and Z=4. 2 belongs to the triclinic system, space group P1 with a=9.6759（7）, b=10.8613（8）, c=15.7642（12） A, a=70.429（3）, b=79.257（4）, g=69.052（4）°, V=1453.63（19） A3 and Z=2. 3 belongs to the monoclinic system, space group P2（1/c） with a=11.1393（4）, b=13.0643（4）, c=17.6600（6） A, b=101.866（2）o, V=2515.09（15） A3 and Z=4. 4 belongs to the monoclinic system, space group C2/c with a=17.8466（3）, b=13.6126（2）, c=21.6710（4） A, b=90.7310（10）°, V=4992.72（14） A3 and Z=8. 5 is of orthorhombic system, space group P212121 with a=10.5555（2）, b=11.8913（2）, c=14.9558（4） A, V=1877.23（5） A3 and Z=4.

Design and synthesis of cyclic acylguanidines as BACE1 inhibitors

Based on the lead compound 1 reported in literature, a series of novel BACE1 inhibitors were designed and synthesized, among which compound 11 exhibited a 14-fold improvement in potency over the lead compound 1. This represents a good lead for the discovery of more promising BACE1 inhibitors for the potential treatment of AD.

Design and synthesis of 3＇-(prop-2-yn-1-yloxy)-biphenyl substituted cyclic acylguanidine compounds as BACE1 inhibitors

Based on the lead compounds 1 and 2, a series of novel BACE1 inhibitors were designed and synthesized,among which compound 9h exhibited a 60 fold improvement in potency over the lead compound 1. This represents a good lead for the discovery of more promising BACE1 inhibitors for the potential treatment of AD. The result also showed that the prop-2-yn-1-yloxy is a suitable fragment for modification of cyclic acylguanidine BACE1 inhibitors.

Design and synthesis of 5-cyclopropyl substituted cyclic acylguanidine compounds as BACE1 inhibitors

By taking compound 1 as a lead, a series of 5-cyclopropyl substituted cyclic acylguanidine compounds were designed and synthesized as BACE1 inhibitors, compound 4d exhibited 84-fold improved inhibition efficiency than lead compound 1. The diphenyl fragment at the P3 position and the substituents at the second phenyl ring were essential for the compounds to achieve improved inhibition efficiency. This SAR studies provides new insights into the design and synthesis of more promising BACE1 inhibitors for the potential treatment of AD.