of the Max - MDC

RNA Chemistry
Eckart Matthes
Hydroxylation of Selected β-L-Deoxycytidine
Derivatives Leads to New, Strong and Selective
Inhibitors of Hepatitis B Virus Replication.
We synthesized a series of new N 4 -hydroxylated L-deoxycytidine
derivatives and evaluated their antiviral activity. Our
results demonstrate that at least L-HyddFC, L-Hyd4C and
L-Hyd4FC act as highly efficient (ED 50 = 0.01-0.05 µM) and
selective inhibitors of hepatitis B virus replication and warrant
further investigation.
Most biological macromolecules contain chiral building
blocks where natural nucleosides have the D-configuration
whereas most amino acids have the L-form. Enzyme reactions
are normally highly stereoselective (nearly stereospecific)
and act mainly on one enantiomer such as D-nucleosides
and L-amino acids. For this reason the L-nucleosides
were underestimated for a long time. Thiacytidine (3TC,
Lamivudine) was the first clinically used L-nucleoside, which
was shown to be a more effective and less cytotoxic antiviral
compound than the corresponding D-enantiomer. The most
surprising aspect was that cellular deoxycytidine kinase
lacks stereospecificity and was found to be able to phosphorylate
3TC and a series of other L-cytidine derivatives,
whereas L-thymidine derivatives seems to be poor substrates
for the cellular thymidine kinase (TK1).
Therefore L-cytidine derivatives have recently gained great
interest as antiviral agents. After phosphorylation to the
triphosphates, however, some of the L-deoxycytidine analogues
were shown to suppress not only the targeted viral
polymerases, but partially also cellular DNA polymerases
which produces antiproliferative toxicity. Between these
compounds are L-didehydrocytidines and L-dideoxycytidines
(L-d4FC, L-d4C, L-ddFC, and L-ddC) with cytoxicity
values (CD 50 ) for HepG2 cells between 8 and 70 µM.
We have hypothesized that the hydroxylation of the N 4 -
aminogroup of L-deoxycytidine analogs might induce steric
and electronic effects resulting in higher selectivity between
viral and cellular DNA polymerase. We therefore synthesized
thirteen hitherto unknown N 4 -hydroxy-modified L-deoxycytidine
analogues (with support of C. Mark, Chemische
Laboratorien, Worms) and evaluated them as potential
inhibitors of hepatitis B virus (HBV)- and human immunodeficiency
virus (HIV)-replication (cooperation with H. Will,
Heinrich-Pette-Institut, Hamburg, S. Urban, University of
Heidelberg, and H. Walter, University of Erlangen-
Nürnberg). These derivatives did not display any activity
against HIV replication but emerged as very powerful
inhibitors of HBV replication.
Figure 1 shows the structures of the most efficient L-cytidine
analogs. The concentrations reducing secreted HBV
DNA to the medium by 50% (ED 50 ) were between 10 and 50
nM for L-HyddFC, L-Hyd4C and L-Hyd4FC (abbreviations see
legend to fig.1) compared with 100 nM for 3TC. Figure 2
NHOH
O
F
NHOH
N N N
O N
O N
O N
NHOH
OH OH OH
O
O
F
Figure 1. Structures of β-Lnucleoside
analogues detected as
most efficient inhibitors of HBV
replication in HepG2.2.15 cells.
L-HyddFC: β-L-2´,3´-dideoxy-
5-fluoro-N 4 -hydroxycytidine,
L-Hyd4C: β-L-2´,3´-didehydro-
2´,3´-dideoxy-N 4 -hydroxycytidine,
L-Hyd4FC: β-L-2´,3´-didehydro-2´,3´-dideoxy-5-fluoro-N
4 -
hydroxycytidine.
L- HyddFC
ED 50 =0.01µM
L- Hyd4C
ED 50 =0.03µM
L- Hyd4FC
ED 50 =0.05µM
Cancer Research 113