Adenosine Analogues as Inhibitors of Trypanosoma brucei Phosphoglycerate Kinase:  Elucidation of a Novel Binding Mode for a 2-Amino-N⁶-Substituted Adenosine

Abstract

As part of a project aimed at structure-based design of adenosine analogues as drugs against African trypanosomiasis, N(6)-, 2-amino-N(6)-, and N(2)-substituted adenosine analogues were synthesized and tested to establish structure-activity relationships for inhibiting Trypanosoma brucei glycosomal phosphoglycerate kinase (PGK), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), and glycerol-3-phosphate dehydrogenase (GPDH). Evaluation of X-ray structures of parasite PGK, GAPDH, and GPDH complexed with their adenosyl-bearing substrates led us to generate a series of adenosine analogues which would target all three enzymes simultaneously. There was a modest preference by PGK for N(6)-substituted analogues bearing the 2-amino group. The best compound in this series, 2-amino-N(6)- [2''(p-hydroxyphenyl)ethyl]adenosine (46b), displayed a 23-fold improvement over adenosine with an IC(50) of 130 microM. 2-[[2''-(p-Hydroxyphenyl)ethyl]amino]adenosine (46c) was a weak inhibitor of T. brucei PGK with an IC(50) of 500 microM. To explore the potential of an additive effect that having the N(6) and N(2) substitutions in one molecule might provide, the best ligands from the two series were incorporated into N(6),N(2)-disubstituted adenosine analogues to yield N(6)-(2''-phenylethyl)-2-[(2'' -phenylethyl)amino]adenosine (69) as a 30 microM inhibitor of T. brucei PGK which is 100-fold more potent than the adenosine template. In contrast, these series gave no compounds that inhibited parasitic GAPDH or GPDH more than 10-20% when tested at 1.0 mM. A 3.0 A X-ray structure of a T. brucei PGK/46b complex revealed a binding mode in which the nucleoside analogue was flipped and the ribosyl moiety adopted a syn conformation as compared with the previously determined binding mode of ADP. Molecular docking experiments using QXP and SAS program suites reproduced this "flipped and rotated" binding mode.

2,N 6 -Disubstituted Adenosine Analogs with Antitrypanosomal and Antimalarial Activities

“…Over the past few years several studies that described the rational targeting of glycolytic enzymes by adenosine derivatives have appeared (6). Although various inhibitors of T. brucei and T. cruzi glyceraldehyde-3-phosphate dehydrogenase (6) and T. brucei phosphoglycerate kinase (5) have been identified, these compounds displayed antitrypanosomal activities only in the low micromolar range; i.e., they were 1 to 2 orders of magnitude less effective than compounds NA42 and NA134.…”

Synthesis, biological evaluation and molecular modeling studies of N6-benzyladenosine analogues as potential anti-toxoplasma agents

“…4-Vinylbenzyl chloride (8) was converted into the azide intermediate as a crude oil and treated with triphenylphosphine followed by hydrolysis to yield benzylamine 9. N 6 -Benzyladenosine analogues 11a-v were synthesized via solution phase parallel synthesis (Scheme 2) [35][36][37]. Introduction of the appropriate benzylamine was achieved by nucleophilic substitution of commercially available 6-chloropurine riboside (10).…”

Virtual Screening of Combinatorial Libraries across a Gene Family: in Search of Inhibitors of Giardia lamblia Guanine Phosphoribosyltransferase

“…A number of groups have reported on the successful design of inhibitors directed against trypanosomal (2,4,(15)(16), leishmanial (6), malarial (19), and tritrichomonal (3, 27) targets active in the 10 nM to 50 M range. However, with the number of compounds that could be generated by combinatorial chemistry growing exponentially, it has become apparent that chemical diversity has surpassed the capacity of high-throughput screening.…”