Design and synthesis of purine analogues as highly specific ligands for FcyB, a ubiquitous fungal nucleobase transporter.

In the course of our study on fungal purine transporters, a number of new 3-deazapurine analogues have been rationally designed, based on the interaction of purine substrates with the Aspergillus nidulans FcyB carrier, and synthesized following an effective synthetic procedure. Certain derivatives have been found to specifically inhibit FcyB-mediated [3H]-adenine uptake. Molecular simulations have been performed, suggesting that all active compounds interact with FcyB through the formation of hydrogen bonds with Asn163, while the insertion of hydrophobic fragments at position 9 and N6 of 3-deazaadenine enhanced the inhibition.

Purine metabolism in plant pathogenic fungi.

In eukaryotic cells, purine metabolism is the way to the production of deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) and plays key roles in various biological processes. Purine metabolism mainly consists of de novo, salvage, and catabolic pathways, and some components of these pathways have been characterized in some plant pathogenic fungi, such as the rice blast fungus Magnaporthe oryzae and wheat head blight fungus Fusarium graminearum. The enzymatic steps of the de novo pathway are well-conserved in plant pathogenic fungi and play crucial roles in fungal growth and development. Blocking this pathway inhibits the formation of penetration structures and invasive growth, making it essential for plant infection by pathogenic fungi. The salvage pathway is likely indispensable but requires exogenous purines, implying that purine transporters are functional in these fungi. The catabolic pathway balances purine nucleotides and may have a conserved stage-specific role in pathogenic fungi. The significant difference of the catabolic pathway in planta and in vitro lead us to further explore and identify the key genes specifically regulating pathogenicity in purine metabolic pathway. In this review, we summarized recent advances in the studies of purine metabolism, focusing on the regulation of pathogenesis and growth in plant pathogenic fungi.

Structure-activity relationships in fungal nucleobases transporters as dissected by the inhibitory effects of novel purine analogues.

We have previously rationally designed, synthesized and tested a number of 3-deazapurine analogues, which inhibit the ubiquitous fungal nucleobase transporter FcyB, through binding in its major substrate binding site, by specifically interacting with Asn163. Here, in an effort to further understand the molecular details of structure-activity relationships in all three major nucleobase transporters of fungi, we extend this study by designing, based on our previous experience, synthesizing and testing further 3-deazapurine analogues. We thus identify seven new compounds with relatively high affinity (19-106 µΜ) for the FcyB binding site. Importantly, four of these compounds can also efficiently inhibit AzgA, a structurally and evolutionary distinct, but functionally similar, purine transporter. Contrastingly, none of the new compounds tested had any effect on the transport activity of the uric acid-xanthine transporter UapA, albeit this being a structural homologue of AzgA. Besides the apparent importance for understanding how nucleobase transporter specificity is determined at the molecular level, our work might constitute a critical step in the design of novel purine-related antifungals.