Figure 1.

(Scheme 1) illustrates the steps for synthesis of a nucleobase-substituent, with tetracyclo-[5.4.2^1,7.O^2,6.O^8,11]3,5-dioxo-4-aza-9,12-tridecadiene (TcT) as an example (documented as “Reppe anhydride”). The chemical reaction is described in detail by Reppe.³⁹ The reaction product of 3 with glycine is 4 whose carboxyl group was transferred immediately with thionyl chloride to the corresponding acid chloride 5 for further processing as described in scheme 3 (Figure 3).