A Concise Microwave-Assisted Synthesis of 2-Aminoimidazole Marine Sponge Alkaloids of the Isonaamines Series

Abstract

A short and efficient route to 1,4-substituted 2-aminoimidazole alkaloids starting from the easily accessible 2-alkylaminopyrimidines and α-bromo aldehydes is reported. The formation of the intermediate imidazo[1,2-a]pyrimidinium salts and subsequent cleavage were facilitated by microwave irradiation. Marine sponge alkaloids preclathridines A, C and isonaamines A, C, D were obtained in high yields using the optimized one-pot two-step procedure.

Key words

natural products - ring opening - cleavage - imidazo[1,2-a]pyrimidin-1-ium salts - 2-aminoimidazoles

References

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2

To avoid contradictory assignment of the same names to the different isonaamine alkaloids, every isonaamine was named in accordance with the parent isolated isonaamidine, as was originally proposed by Y. Kashman et al.¹

18

Crystallographic data for 1e reported in this paper have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication No. CCDC 679428. Copies of the data can be obtained, free of charge, on application to CCDC, 12 Union Road, Cambridge CB 2 1EZ, UK [fax: [phone] or E-mail: [e-mail]]. Some selected crystallographic data: crystal system, space group: crystal system triclinic; space group P1; cell parameters: a = 5.8703(16), b = 9.0133(8), c = 16.155(2) Å; α = 93.778(9), β = 91.640(10), γ = 94.461(10)°; V = 849.843 ų; Z = 2, Z′ = 0; R-factor 4.9%.