Novel non-nucleoside human cytomegalovirus inhibitors based upon TSAO nucleoside derivatives: Structure-activity relationships

Article abstract of DOI:10.1080/15257770701490431

TSAO derivatives are a unique group of potent and highly specific inhibitors of HIV-1 replication. We have recently reported 4′-ureido TSAO derivatives that are devoid of anti-HIV-1 activity, but inhibit human cytomegalovirus with an activity comparable t

Full text of DOI:10.1080/15257770701490431

Nucleosides, Nucleotides, and Nucleic Acids, 26:625–628, 2007
Copyright ꢀ Taylor & Francis Group, LLC
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ISSN: 1525-7770 print / 1532-2335 online
DOI: 10.1080/15257770701490431
NOVEL NON-NUCLEOSIDE HUMAN CYTOMEGALOVIRUS
INHIBITORS BASED UPON TSAO NUCLEOSIDE DERIVATIVES:
STRUCTURE-ACTIVITY RELATIONSHIPS
Sonia de Castro
Instituto de Qu´ımica Me´dica (CSIC), Madrid, Spain
2
Graziela Andrei, Robert Snoeck, and Jan Balzarini
Rega Institute for Medical
2
research, K.U. Leuven, Leuven, Belgium
Mar´ıa-Jose´ Camarasa and Sonsoles Vela´zquez
Instituto de Qu´ımica Me´dica
2
(CSIC), Madrid, Spain
TSAO derivatives are a unique group of potent and highly specific inhibitors of HIV-1 replica-
2
tion. We have recently reported 4 ꢁꢁ-ureido TSAO derivatives that are devoid of anti-HIV-1 activity,
but inhibit human cytomegalovirus with an activity comparable to that of Ganciclovir. We herein
report the synthesis and biological evaluation of novel 4 ꢁꢁ-ureido TSAO derivatives in order to evalu-
ate the structural features required for anti-HCMV activity. Interestingly, these studies revealed that
the compounds may inhibit HCMV at the DNA polymerase step via a non-nucleoside mechanism.
Keywords TSAO nucleosides; cytomegalovirus; ureidonucleosides; HCMV inhibitors
INTRODUCTION
Human cytomegalovirus (HCMV) is an ubiquitous member of the
herpesvirus family. Although it rarely causes symptomatic disease in im-
munocompetent individuals, it is responsible for a variety of severe, of-
ten life-threatening diseases (i.e., pneumonia, retinitis) in immunocompro-
mized or immunosuppressed individuals (transplant recipients and in AIDS
patients).[1] HCMV also is a major cause of congenital malformation in
newborn children.[2] Currently approved anti-HCMV agents (ganciclovir,
foscarnet, valganciclovir, cidofovir, and formivisen) inhibit the viral DNA
polymerase.[3] However, these drugs suffer from a number of drawbacks
such as dose-limiting bone marrow and kidney toxicity, unfavorable pharma-
cokinetic properties, as well as the emergence of single and multiple drug
We thank Susana Ruiz for excellent technical assistance. We also thank the Spanish MEC (project
SAF 2006-12713-C02-01) for financial support.
Address correspondence to Sonsoles Vela´zquez, Instituto de Qu´ımica Me´dica (CSIC), Juan de la
Cierva 3, Madrid 28006, Spain. E-mail: iqmsv29@iqm.csic.es
625

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S. de Castro et al.
SCHEME 1 Reagents and conditions (i) RNCO, NaH, THF, 70◦C (ii) (iii) TBDMSCI, Py, rt (iv) 1N HCI,
methanol, 0◦C (v) NH3, methanol.
resistance.[4] Therefore, there is a need for new anti-HCMV compounds,
potent, safe, orally bioavailable, and with novel mechanisms of action.
We have recently reported[5] that 4ꢁꢁ-ureido-TSAO derivatives (TSAO
compounds are a particular and peculiar group of potent and highly spe-
cific inhibitors of HIV-1 replication[6]) are devoid of anti-HIV-1 activity, but
are potent and selective inhibitors of HCMV in cell culture. The proto-
type compound (5) inhibit HCMV replication with an activity comparable
to that of Ganciclovir.[5] However, the highly modified structures of these
TSAO nucleosides suggest a different mechanism of inhibition of the viral
replication.
In order to evaluate the structural features required for anti-HCMV
activity, modifications at the 4ꢁꢁ-ureido moiety, and replacement of the 2ꢁ
and/or 5ꢁ tert-butyldimethylsilyl groups by other groups, have been per-
formed. In this communication we report on the synthesis, biological evalua-
tion, and preliminary time of addition experiments of these novel 4ꢁꢁ-ureido
TSAO derivatives.
RESULTS AND DISCUSSION
Synthesis
4ꢁꢁ-Subtituted TSAO-m3T derivatives, bearing different ureido groups at
the 4ꢁꢁ-position (6–8), were prepared, in moderate to good yields, by reaction
of 1 (Scheme 1) with an excess of conveniently functionalized isocyanates
in the presence of NaH in dry acetonitrile at 70◦C. On the other hand, com-
pounds substituted with other silyl groups at the 5ꢁ position, such as 5ꢁ-O-
tert-hexyldimethylsilyl (TDS) (9) or 5ꢁ-O-triisopropylsilyl (TIPS) (10), were
prepared in good yields by reaction of the corresponding 5ꢁ-O-protected
TSAO derivatives 2 or 3 with benzoyl isocyanate, in the presence of NaH at

Human Cytomegalovirus Inhibitors
627
70◦C.[7] Next, 4ꢁꢁ-benzoylureido-TSAO-m3T derivatives bearing other groups
at 2ꢁ- and 5ꢁ-positions were prepared as follows. A reaction of 5 with tetrabuty-
lamonium fluoride in dry THF gave the 2ꢁ,5ꢁ-O-deprotected 4ꢁꢁ-benzoyl ure-
ido derivative 12 that was silylated (TBDMSCl/pyridine) to give compound
13. Similarly, treatment of 5 with a 0.1N solution of HCl in methanol at 0o C
gave 14 in a 59% yield. Finally, reaction of 4[9] with benzoyl isocyanate in dry
THF at room temperature gave the 2ꢁ-acetyl-5ꢁ-benzoyl-4ꢁꢁ-benzoyl derivative
11 (91% yield). Treatment of 11 with NH3 in methanol at 0o C gave the 5ꢁ-
benzoyl-2ꢁ-O-deprotected derivative 15 in low yield.
Biological Evalutation
The novel TSAO derivatives (6–10, 11–15) were evaluated against repli-
cation of human CMV in cell culture. Several compounds showed pro-
nounced antiviral activity at concentrations in the lower micromolar range
(i.e., 0.12–1.5 µM) at a concentration below their toxicity threshold. Com-
pounds 9 and 10, in which the 5ꢁ-tert-buthyldimenthylsilyl groups were re-
placed by other silyl groups, showed a similar activity to that of com-
pound 5 (EC50 = 1.1 and 1.2 µM versus 0.8 µM), although they were more
toxic (CC50 => 50 µM versus 200 µM). In contrast, 2ꢁ-acetyl-5ꢁ-benzoyl-
4ꢁꢁ-benzoyl-ureido derivative 11 was devoid of antiviral activity at subtoxic
concentrations. Also, compounds containing a free OH at 2ꢁ- and/or 5ꢁ-
position(s) (13–15) were devoid of antiviral activity at subtoxic concentra-
tions. Given the nucleoside type structure of these compounds, one would
expect that these new anti-HCMV compounds may act via a “conventional”
nucleoside mechanism involving 5ꢁ-phosphorylation. However, the biologi-
cal results point to a different mechanism of action since both 2ꢁ and 5ꢁ-OH
groups need to be “blocked” with silyl groups to show anti-HCMV activity.
Indeed, this new family of agents seem to act via a novel non-nucleosidic
mechanism. Thus, the preliminary time of addition experiments, carried
out with the prototype compound 5 suggests that this compound acts be-
fore GCV and HPMPC (compounds known to affect a late phase of HCMV
replicative cycle). Interestingly, these studies revealed that the compounds
may inhibit HCMV at the DNA polymerase step via a non-nucleoside mecha-
nism. A more detailed SAR study of these nucleosides and of the mechanism
of action is now in progress.
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