Synthesen in der Purinreihe, XV1) Synthesen von Xanthinium- und Guaninium-betainen

Metal complexes of xanthine and its derivatives: Synthesis and biological activity

Xanthine and its derivatives are considered an important class of N-heterocyclic purine compounds that have gained significant importance in medicinal chemistry. N-heterocyclic carbene (NHC) and N-coordinated metal complexes of xanthine and its derivatives have revealed a range of new possibilities for their use as therapeutic agents in addition to their established catalytic behavior. The metal complexes of xanthine and its derivatives have been designed and synthesized for the exploration of their potential therapeutic applications. These metal complexes based on the xanthine scaffold exhibited various potential medicinal applications including anticancer, antibacterial, and antileishmanial activity. The metal complexes of xanthine and its derivatives shall pave the way for the rational design and development of new therapeutic agents. In the present comprehensive review, we highlighted the recent advancements in the synthesis and medicinal applications of metal complexes based on N-heterocyclic carbene (NHC) derived from xanthine scaffolds.

Facile N9-Alkylation of Xanthine Derivatives and Their Use as Precursors for N-Heterocyclic Carbene Complexes

The xanthine-derivatives 1,3,7-trimethylxanthine, 1,3-dimethyl-7-benzylxanthine and 1,3-dimethyl-7-(4-chlorobenzyl)xanthine are readily ethylated at N9 using the cheap alkylating agents ethyl tosylate or diethyl sulfate. The resulting xanthinium tosylate or ethyl sulfate salts can be converted into the corresponding PF₆^- and chloride salts. The reaction of these xanthinium salts with silver(I) oxide results in the formation of different silver(I) carbene-complexes. In the presence of ammonia, ammine complexes [Ag(NHC)(NH₃)]PF₆ are formed, whilst with Et₂NH, the bis(carbene) salts [Ag(NHC)₂]PF₆ were isolated. Using the xanthinium chloride salts neutral silver(I) carbenes [Ag(NHC)Cl] were prepared. These silver complexes were used in a variety of transmetallation reactions to give the corresponding gold(I), ruthenium(II) as well as rhodium(I) and rhodium(III) complexes. The compounds were characterized by various spectroscopic methods as well as X-ray diffraction.

N2,N2,7-trimethylguanine, a new trimethylated guanine natural product from the New Zealand ascidian, Lissoclinum notti

From the New Zealand ascidian, Lissoclinum notti a new natural product, N2,N2,7-trimethylguanine (1) has been isolated. The structure of 1 was elucidated by analysis of spectroscopic data.