Synthesis of 2′‐Deoxy‐5‐(isothiazol‐5‐yl)uridine and Its Interaction with the HSV‐1 Thymidine Kinase

Abstract

(1 3.11.96) 2'-Deoxy-5-(isothiazol-5-yl)uridine (12) was synthesized starting from 2'-deoxy-5-iodouridine using a Pdcatalysed cross-coupling reaction with propiolaldehyde diethyl acetal followed by deprotection and ring closure using thiosulfate. 2'-Deoxyuridine 12 has a particular place among the 5-heteroaryl-substituted 2'-deoxyuridines in that it has a high affinity for herpes simplex virus type 1(HSV-1)-encoded thymidine kinase (TK) without antiviral activity. Biochemical studies revealed that 12 is a substrate for viral TK. We further investigated the interaction of 12 with the HSV-1 thymidine kinase. The conformation of 12 in solution was established by NMR spectroscopy. The most stable conformer 12A has the S-atom of the isothiazole ring placed in the neighbourhood of the C(4)=0 group of the pyrimidine moiety. The compound was docked in its most stable conformation in the active site of HSV-1 TK and subjected to energy minimization. This demonstrated that the isothiazole moiety binds in a cavity lined by the side chains ofTyr-132, Arg-163, Ala-167, and Ala-168 and that the C(3) atom of the isothiazole moiety is located in close proximity of the phenolic 0-atom of Tyr-132 and the aliphatic part of the Arg-163 side chain.Introduction. -The structure-activity-relationship study of 5-substituted 2'-deoxyuridines started with the historical discovery of 2'-deoxy-5-iodouridine as an anti-herpes agent [l]. The mode of action of 5-substituted 2'-deoxyuridines has since long been studied, and it is well documented that these compounds have to be phosphorylated to their mono-, di-, and triphosphate and that these metabolites are responsible for the biological activity. In their monophosphate form, some 5-substituted 2'-deoxyuridines are efficient inhibitors of thymidylate synthase [2]. In their triphosphate form, these nucleosides interfere with DNA synthesis by inhibiting DNA polymerases and/or by functioning as alternative substrates thus being incorporated into DNA. Whatever the mechanism, the first step in the anabolism to the active metabolite is the phosphorylation by nucleoside kinases. With respect to the 5-substituted 2'-deoxyuridines that are active against HSV-1, this phosphorylation is carried out by the viral thymidine kinase. The thymidine kinase (TK) encoded by herpes simplex virus type 1 (HSV-1) has a broader substrate specificity than the human enzymes so that modified nucleosides can be selectively activated in the HSV-1-infected cells.Recently, a study was undertaken to analyse the affinity of several 5-substituted 2'-deoxyuridines for the HSV-1-encoded TK and to relate this affinity with structural data [3-81. In Table I , an overview is given of the compounds synthesized (see Scheme for general Formula), together with their TK affinity. Compounds with a low affinity for the

Understanding the Binding of 5-Substituted 2‘-Deoxyuridine Substrates to Thymidine Kinase of Herpes Simplex Virus Type-1

“…Interestingly, in the 2-thienyl series of compounds, coplanarity is stabilized by an interaction between the O4 carbonyl group of the uracil base and the sulfur atom of the thiophene ring (Figure , structure A ). A similar orientation for the isothiazole derivative (Figure , structure B ) has been deduced from its NMR spectrum and quantum-chemical calculations, which predict a stability of 17 kJ/mol of the NMR observed orientation relative to the other possibility , structures C and D ).…”

Exploring the active site of herpes simplex virus type-1 thymidine kinase by X-ray crystallography of complexes with aciclovir and other ligands

“…19 The structural results presented here imply that this could be due to the size of the bromovinyl moiety, by comparison with the iodine of IDU or AHIU or the bromothienyl group of BTDU, being such as to give an optimal fit to this site (allowing for the observed movement of Tyr-132), in terms of van der Waals interactions. The compound 5-thienyluridine, not yet examined by us, shows a strength of binding 18,19 similar to BTDU; it is possible the five-membered ring of this and BTDU is slightly too bulky for the subsite. Figure 5b shows an overlay of the active site regions of the TK/ ganciclovir and TK/BVDU complexes, and emphasizes the considerable, albeit flat, volume which is available for ligand binding in the enzyme.…”

Docking and Antiherpetic Activity of 2-Aminobenzo[de]-isoquinoline-1,3-diones

“…It is observed that the 2-amino group, carbonyl groups and the nitrogen atom of the benzoisoquinoline-1,3-dione moiety form five H-bond interactions with Glu63 and Tyr172, with bond lengths of 2.53, 3.27, 3.01, 3.38 and 3.31 Å, respectively. In addition, the hydrophobic interactions with Tyr172 alongside the phenyl ring with Tyr132 and Trp88 appear to constrain the molecule in close proximity with the amino acids forming the aforementioned hydrogen bonding [24,25,26].…”