Felicia Phei Lin Lim

1,3,5-Triazine-based analogues of purine: from isosteres to privileged scaffolds in medicinal chemistry.

Purines can be considered as the most ubiquitous and functional N-heterocyclic compounds in nature. Structural modifications of natural purines, particularly using isosteric ring systems, have been in the focus of many drug discovery programs. Fusion of 1,3,5-triazine ring with pyrrole, pyrazole, imidazole, 1,2,3-triazole or 1,2,4-triazole results in seven bicyclic heterocyclic systems isosteric to purine. Application of the isosterism concept for the development of new compounds with therapeutic potential in areas involving purinergic regulation or purine metabolism led to significant advances in medicinal chemistry of the azolo[1,3,5]triazines. These 1,3,5-triazine-based purine-like scaffolds significantly increase level of molecular diversity and allow covering chemical space in the important areas of medicinal chemistry. Some of these azolo[1,3,5]triazine systems have become privileged scaffolds in the development of inhibitors of various kinases, phosphodiesterase, xanthine oxidase, and thymidine phosphorylase, antagonists of adenosine and corticotropin-releasing hormone receptors, anticancer and antiviral agents.

A multicomponent reaction of 2-aminoimidazoles: microwave-assisted synthesis of novel 5-aza-7-deaza-adenines

An efficient and highly selective multicomponent synthesis of 4-aminoimidazo[1,2-a][1,3,5]triazines, which are 5-aza-7-deaza-isosteres of adenine, was developed. The reaction of 2-aminoimidazoles, triethyl orthoformate and cyanamide under microwave irradiation proceeded regioselectively to provide a library of novel 5-aza-7-deaza-adenines in good yields and purity. The developed method was demonstrated to be scalable and highly reproducible in three different monomode microwave reactors. A rearrangement was proposed to explain the high selectivity of the reaction.

Crystal structure of 7-(4-methylphenyl)imidazo[1,2-a][1,3,5]triazin-4-amine, C12H11N5

Abstract C12H11N5, monoclinic, P21/n (no. 14), a = 7.3455(1) Å, b = 12.2470(1) Å, c = 12.1689(1) Å, β = 103.505(1)°, V = 1064.45(2) Å3, Z = 4, Rgt(F) = 0.0365, wRref(F2) = 0.0987, T = 100 K.

Synthesis of 3-(5-amino-1H-1,2,4-triazol-3-yl)propanamides and their tautomerism

Two complementary pathways for the preparation of N-substituted 3-(5-amino-1H-1,2,4-triazol-3-yl)propanamides (5) were proposed and successfully realized in the synthesis of 20 representative examples. These methods use the same types of starting materials viz. succinic anhydride, aminoguanidine hydrochloride, and a variety of amines. The choice of the pathway and sequence of the introduction of reagents to the reaction depended on the amine nucleophilicity. The first pathway started with the preparation of N-guanidinosuccinimide, which then reacted with amines under microwave irradiation to afford 5. The desired products were successfully obtained in the reaction with aliphatic amines (primary and secondary) via a nucleophilic opening of the succinimide ring and the subsequent recyclization of the 1,2,4-triazole ring. This approach however failed when less nucleophilic aromatic amines were used. Therefore, an alternative pathway, with the initial preparation of N-arylsuccinimides and their subsequent reaction with aminoguanidine hydrochloride under microwave irradiation, was applied. The annular prototropic tautomerism in the prepared 1,2,4-triazoles 5 was studied using NMR spectroscopy and X-ray crystallography.

A one-pot, multicomponent reaction for the synthesis of novel 2-alkyl substituted 4-aminoimidazo[1,2-a][1,3,5]triazines

A highly selective, one-pot, three-component synthesis of novel 2-alkyl-substituted 4-aminoimidazo[1,2-a][1,3,5]triazines has been developed. The scope of the method was explored in two dimensions, varying the structures of trialkyl orthoesters and 2-aminoimidazoles in their reactions with cyanamide. Conveniently performed under microwave irradiation, this method was also proved to be efficient under conventional heating. A library of 24 novel compounds was prepared in high purity using this multicomponent approach. Molecular and crystal structures of representative molecules were studied using X-ray crystallography.

A microwave-assisted synthesis of 3-(5-amino-1 H -1,2,4-triazol-3-yl)propanamides from succinimides

1,2,4-Triazole is a privileged scaffold in medicinal and agricultural chemistry. Many useful and structurally diverse compounds have been prepared using 5-amino-1,2,4-triazoles as building block. Herein, we report a new microwave-assisted synthesis of 3-(5-amino-1H-1,2,4-triazol-3-yl)propanamides via two complementary approaches. The first approach involved the initial preparation of N-guanidinosuccinimide, which then reacted with amines under microwave irradiation affording corresponding 3-(5-amino-1H-1,2,4-triazol-3-yl)propanamides. The desired products were successfully obtained in the reaction with aliphatic amines (primary and secondary) via a nucleophilic opening of the succinimide ring and the subsequent recyclization affording the 1,2,4-triazole ring. This approach failed when less nucleophilic aromatic amines were used. Therefore, we designed an alternative pathway with the initial preparation of N-arylsuccinimides and their subsequent reaction with aminoguanidine hydrochloride under microwave irradiation. In this case, the 1,2,4-triazole ring closure was most efficiently achieved in the presence of organic base. These two approaches complement each other allowing preparation of a diverse library of 3-(5-amino-1H-1,2,4-triazol-3-yl)propanamides.