Mechanism and structure based design of inhibitors of AMP and adenosine deaminase.

Inhibitors of the enzyme adenosine monophosphate deaminase (AMPD) show interesting levels of herbicidal activity. An enzyme mechanism-based approach has been used to design new inhibitors of AMPD starting from nebularine (6) and resulting in the synthesis of 2-deoxy isonebularine (16). This compound is a potent inhibitor of the related enzyme adenosine deaminase (ADA; IC50 16 nM), binding over 5000 times more strongly than nebularine. It is proposed that the herbicidal activity of compound 16 is due to 5́-phosphorylation in planta to give an inhibitor of AMPD. Subsequently, an enzyme structure-based approach was used to design new non-ribosyl AMPD inhibitors. The initial lead structure was discovered by in silico screening of a virtual library against plant AMPD. In a second step, binding to AMPD was further optimised via more detailed molecular modeling leading to 2-(benzyloxy)-5-(imidazo[2,1-f][1,2,4]triazin-7-yl)benzoic acid (36) (IC50 300 nM). This compound does not inhibit ADA and shows excellent selectivity for plant over human AMPD.

Identification of Adenosine Deaminase Inhibitors by Metal-binding Pharmacophore Screening.

Adenosine deaminase (ADA) is a human mononuclear Zn2+ metalloenzyme that converts adenosine to inosine. ADA is a validated drug target for cancer, but there has been little recent work on the development of new therapeutics against this enzyme. The lack of new advancements can be partially attributed to an absence of suitable assays for high-throughput screening (HTS) against ADA. To facilitate more rapid drug discovery efforts for this target, an in vitro assay was developed that utilizes the enzymatic conversion of a visibly emitting adenosine analogue to the corresponding fluorescent inosine analogue by ADA, which can be monitored via fluorescence intensity changes. Utilizing this assay, a library of ∼350 small molecules containing metal-binding pharmacophores (MBPs) was screened in an HTS format to identify new inhibitor scaffolds against ADA. This approach yielded a new metal-binding scaffold with a Ki value of 26±1 µM.

Modifications of flexible nonyl chain and nucleobase head group of (+)-erythro-9-(2's-hydroxy-3's-nonyl)adenine [(+)-EHNA] as adenosine deaminase inhibitors.

A series of terminal nonyl chain and nucleobase modified analogues of (+)-EHNA (III) were synthesized and evaluated for their ability to inhibit adenosine deaminase (ADA). The constrained carbon analogues of (+)-EHNA, 7a-7h, 10a-c, 12, 13, 14 and 17a-c appeared very potent with Ki values in the low nanomolar range. Thio-analogues of (+)-EHNA 24a-e wherein 5'C of nonyl chain replaced by sulfur atom found to be less potent compared to (+)-EHNA. Docking of the representative compounds into the active site of ADA was performed to understand structure-activity relationships. Compounds 7a (Ki: 1.1nM) 7b (Ki: 5.2nM) and 26a (Ki: 5.9nM) showed suitable balance of potency, microsomal stability and demonstrated better pharmacokinetic properties as compared to (+)-EHNA and therefore may have therapeutic potential for various inflammatory diseases, hypertension and cancer.

Synthesis of new nebularine analogues and their inhibitory activity against adenosine deaminase.

A number of new 2,6-disubstituted-1-deazanebularine analogues as well as two structurally related pyrazole-fused tricyclic nucleosides were prepared. Their synthesis was carried out by the conversion of 6-amino-2-picoline to a suitable 1-deazapurine, followed by a Vorbrüggen type glycosylation and subsequent elaboration of the condensed pyrazole ring. The synthesized nebularine analogues proved to be weak adenosine deaminase inhibitors.

Syntheses, structures, and antimicrobial activity of new remarkably light-stable and water-soluble tris(pyrazolyl)methanesulfonate silver(I) derivatives of N-methyl-1,3,5-triaza-7-phosphaadamantane salt - [mPTA]BF4.

Two new silver(I) complexes of formula [Ag(mPTA)4](Tpms)4(BF4) (1) and [Ag(Tpms)(mPTA)](BF4) (2) (mPTA = N-methyl-1,3,5-triaza-7-phosphaadamantane cation, Tpms = tris(pyrazol-1-yl)methanesulfonate anion) have been synthesized and fully characterized by elemental analyses, (1)H and (31)P{(1)H} NMR, ESI-MS, and IR spectroscopic techniques. The single-crystal X-ray diffraction study of 1 discloses a noncoordinated nature of the Tpms species, existing as counterions around the highly charged metal center [Ag(mPTA)](5+), 1 being the first reported coordination compound bearing a κ(0)-Tpms. 1 features high solubility and stability in water (S25 °C ≈ 30 mg·mL(-1)). The two complexes interact with calf thymus DNA via intercalation mode, binding to the BSA with decrease of its tryptophan fluorescence with a static quenching mechanism. The two new silver complexes exhibit significant antibacterial and antifungal activities screened in vitro against the standard strains of Staphylococcus aureus, Enterococcus faecalis, Pseudomonas aeruginosa, Escherichia coli, and Candida albicans.

"Reverse" carbocyclic fleximers: synthesis of a new class of adenosine deaminase inhibitors.

A series of flexible carbocyclic pyrimidine nucleosides has been designed and synthesized. In contrast to previously reported "fleximers" from our laboratory, these analogues have the connectivity of the heterocyclic base system "reversed", where the pyrimidine ring is attached to the sugar moiety, rather than the five membered imidazole ring. As was previously seen with the ribose fleximers, their inherent flexibility should allow them to adjust to enzyme binding site mutations, as well as increase the affinity for atypical enzymes. Preliminary biological screening has revealed surprising inhibition of adenosine deaminase, despite their lack of resemblance to adenosine.

Synthesis of fluorinated purine and 1-deazapurine glycosides as potential inhibitors of adenosine deaminase.

The synthesis of 2- and 6-trifluoromethylated purines and 1-deazapurines was performed by formal [3 + 3]-cyclization reactions of 5-aminoimidazoles with a set of trifluoromethyl-substituted 1,3-CCC- and 1,3-CNC-dielectrophiles. The corresponding fluorinated nucleosides were synthesized by glycosylation of 9-unsubstituted purines and 1-deazapurines with peracetylated ß-ribose, ß-glucose, and rhamnose and subsequent deprotection. These scaffolds can be considered as potential inhibitors of adenosine deaminase (ADA) and inosine monophosphate dehydrogenase (IMPDH) enzymes.

Investigations into the origin of the molecular recognition of several adenosine deaminase inhibitors.

Inhibitors of adenosine deaminase (ADA, EC 3.5.4.4) are potential therapeutic agents for the treatment of various health disorders. Several highly potent inhibitors were previously identified, yet they exhibit unacceptable toxicities. We performed a SAR study involving a series of C2 or C8 substituted purine-riboside analogues with a view to discover less potent inhibitors with a lesser toxicity. We found that any substitution at C8 position of nebularine resulted in total loss of activity toward calf intestinal ADA. However, several 2-substituted-adenosine, 8-aza-adenosine, and nebularine analogues exhibited inhibitory activity. Specifically, 2-Cl-purine riboside, 8-aza-2-thiohexyl adenosine, 2-thiohexyl adenosine, and 2-MeS-purine riboside were found to be competitive inhibitors of ADA with K(i) values of 25, 22, 6, and 3 µM, respectively. We concluded that electronic parameters are not major recognition determinants of ADA but rather steric parameters. A C2 substituent which fits ADA hydrophobic pocket and improves H-bonding with the enzyme makes a good inhibitor. In addition, a gg rotamer about C4'-C5' bond is apparently an important recognition determinant.