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The synthesis of several (2-oxaadamant-1-yl)amines is reported. They were evaluated as NMDA receptor antagonists and several of them were more active than amantadine, but none was more potent than memantine. None of the tested compounds displayed antiviral activity. Two of the derivatives showed a significant level of trypanocidal activity. Based on the interesting and widely observed biological activity of amantadine, memantine, and NGP1-01, we therefore sought to explore the biological profile of (2-oxaadamant-1yl)amine derivatives. In this paper, we report the synthesis of several (2-oxaadamant-1-yl)amines and related compounds and their pharmacological evaluation as NMDA receptor antagonists, and antivirals and trypanocidals agents. Results and discussion Starting from the known diketone 1, 7 we have prepared amines 2-4, 7, 8, and 10-15 using classical methods in amine chemistry (see Scheme 1). Secondary amines 2a and 2b were obtained in high yields following a known general procedure that involves reductive amination of diketone 1. 8 Thus, reaction of 1 with benzylamine followed by reduction with LiAlH 4 led to amine 2a in 58% yield. Similarly, reductive amination of 1 with phenethylamine furnished amine 2b in 51% yield. Reductive alkylation of amines 2a,b with formaldehyde and sodium cyanoborohydride afforded tertiary amines 3a,b in high yields. Hydrogenolysis of the benzyl group of amines 2a and 3a led to 7 and 4, respectively. Finally, alkylation of 2a with benzyl chloride led to 8 in 85% yield. Alcohols of general structure 5 were prepared using a general method developed some time ago by our group. 9 Several attempts to carry out the substitution of the hydroxyl group of 5 by a wide range of amines led to the recovery of the starting material. Moreover, the attempted Ritter reaction of 5c with acetonitrile in acidic medium led to the known enone 6 in high yield. 9c However, reaction of 5a-c with aqueous hydrazine led to hydrazines 9a-c in high yields, probably due to the -effect ensuring a higher nucleophilicity of hydrazine. Even though the reaction failed in the case of 5d. Catalytic hydrogenation of 9a,b furnished amines 10a,b in high yields. Surprisingly, 9c led to a mixture of the expected amine 10c and the cyclohexyl derivative 10d in the ratio of 3:4. Both products were separated by column chromatography. Reductive methylation of amines 10a and 10b with formaldehyde and sodium cyanoborohydride afforded tertiary amines 11a and 11b, respectively. In a similar way, reductive alkylation of 10b with acetaldehyde or benzaldehyde led to amines 12 and 13, respectively. Finally, secondary amine 15 was synthesized from benzylamine 13 by reductive alkylation followed by catalytic debenzylation in good overall yield. The structure of all new compounds was confirmed by elemental analysis or by accurate mass measurement, IR, 1 H NMR, 13 C NMR, and mass spectral data. In the last years there has been an intensive research on the development of new NMDA receptor antagonists, since this subtype of receptors has been involved in the apoptotic process that develops during neurodegenerative diseases. Memantine is a non-competitive and low affinity blocker that acts selectively on NMDA receptors that is being used in Alzheimer's disease to slow down its progression. 10
Synthesis and pharmacological evaluation of (2-oxaadamant-1- yl)amines