Differentiation between [1,2,4]triazolo[1,5-a] pyrimidine and [1,2,4]triazolo[4,3-a]-pyrimidine regioisomers by 1H-15N HMBC experiments.
The condensation of malonoaldehyde derivatives with either a 3-amino-[1,2,4]-triazole or a 3,5-diamino-[1,2,4]-triazole precursor was studied. In agreement with previous reports, two different bicycles, namely, bearing the regioisomeric [1,2,4]triazolo[1,5-a]pyrimidine (1) or [1,2,4]triazolo[4,3-a]pyrimidine (2) structural surrogates, could be obtained. We found that, depending on the triazole precursor, only one regioisomer resulted, either of the 1 or 2 series. We also observed that these two structural surrogates could be unambiguously differentiated by indirectly measuring their (15)N chemical shifts by (1)H-(15)N HMBC experiments. The occasional conversion of [1,2,4]triazolo[4,3-a]pyrimidines to the [1,2,4]triazolo[1,5-a]pyrimidine counterparts could be unequivocally determined by (15)N NMR data.
Salgado
Antonio
A
Department of Medicinal Chemistry, Centro Nacional de Investigaciones Oncológicas, Melchor Fernández Almagro 3, 28029 Madrid, Spain. asalgado@cnio.es
Varela
Carmen
C
García Collazo
Ana María
AM
Pevarello
Paolo
P
D009682:Magnetic Resonance Spectroscopy / Q000592:standards; D015394:Molecular Structure; D009587:Nitrogen Isotopes; D011522:Protons; D011743:Pyrimidines / Q000737:chemistry*; D012015:Reference Standards; D013237:Stereoisomerism; D014230:Triazoles / Q000737:chemistry*
C419143:1,2,4-triazole(1,5a)pyrimidine; D009587:Nitrogen Isotopes; D011522:Protons; D011743:Pyrimidines; D014230:Triazoles