CAUTION IN USING N-15-C-13 SPIN-SPIN COUPLING FOR DETERMINING (BIO)SYNTHETIC PATHWAYS

A recent communication by Suzuki et al.1 purported asuccessful application of l5N,l3C double label technique fordetermining the synthetic pathway to adenine from hydrogencyanide and formamide.1 The idea was the same as the well-established 13C double label technique which depends uponthe fairly large coupling constants between directly bondednuclei.2 It was assumed that the doubly labeled precursorscould be detected unambiguously by the coupling constantsy(l3C-15N), whereas the recombined C-N bonds in theproducts would lack these couplings. This is a reasonable approach, but unfortunately the magnitude of directly bonded15N-13C coupling constants is not fully understood.3 In par-ticular, in the course of the structural investigation using15N-enriched nucleic acid derivatives, we have found nu-merous unusually small l5N-l3C coupling constants for directly bonded pairs,4 and therefore the application of l5N,13Cdouble label technique used to determine synthetic pathwaysmay be unreliable.© 1979, American Chemical Society. All rights reserved.