Total synthesis of [(15)N]-labelled C6-substituted purines from [(15)N]-formamide—easy preparation of isotopically labelled cytokinins and derivatives

Cytokinins (CKs) and their metabolites and derivatives are essential for cell division, plant growth regulation and development. They are typically found at minute concentrations in plant tissues containing very complicated biological matrices. Therefore, defined standards labelled with stable isotopes are required for precise metabolic profiling and quantification of CKs, as well as in vivo elucidation of CK biosynthesis in various plant species. In this work, 11 [(15)N]-labelled C6-purine derivatives were prepared, among them 5 aromatic (4, 5, 6, 7, 8) and 3 isoprenoid (9, 10, 11) CKs. Compared to current methods, optimized syntheses of 6-amino-9H-[(15)N(5)]-purine (adenine) and 6-chloro-9H-[(15)N(4)]-purine (6-chloropurine) were performed to achieve more effective, selective and generally easier approaches. The chemical identity and purity of prepared compounds were confirmed by physico-chemical analyses (TLC; HRMS; HPLC–MS; (1)H, (13)C, (15)N NMR). The presented approach is applicable for the synthesis of any other desired [(15)N(4)]-labelled C6-substituted purine derivatives.