Antiviral agents are now need for the society . So here is the brief intro about it

1. z
Antiviral drugs

2. The classification and biochemistry of viruses
Viruses are unique organisms. They are the smallest of
all self-replicating organisms, able to pass through filte
that retain the smallest bacteria.
The simplest viruses contain a small amount of DNA o
RNA surrounded by an uncomplicated protein coat.
Some of the more complex viruses have a lipid bilayer
membrane surrounding the nucleic acid.
Viruses must replicate in living cells, which has led
many to argue that viruses are not even living organism
but that they somehow exist at the interface of the livin
and the nonliving.

3. A typical DNA virus will enter the nucleus of the host c
where viral DNA is transcribed into messenger RN
(mRNA) by host cell RNA polymerase. mRNA is th
translated into virus-specific proteins that facilit
assembly, maturation, and release of newly formed vi
into surrounding tissues.
RNA viruses are somewhat different, in that th
replication relies on enzymes in the virus itself to synthes
mRNA. An adult virus possesses only one type of nucl
acid (either a DNA or an RNA genome).
Another unique feature of viruses is that their organiz
structure is completely lost during replication within
host cell; the nucleic acid and proteins exist dispersed in
cytoplasm.

4. Classification of viruses
Viruses are classified on the basis of several features:
• Nucleic acid content (DNA or RNA)
• Viral morphology (helical, icosahedral)
• Site of replication in cell (cytoplasm or nucleus)
• Coating (enveloped or non enveloped)
• Serological typing (antigenic signatures)
• Cell types infected (B lymphocytes, T lymphocytes,
monocytes)

5. Amantadine and congeners
-Amantadine and Rimantadine are tricyclic amines.
Mechanism of action
(a) they inhibit an early step in viral replication, most
likely viral uncoating, and
(b) in some strains, they affect a later step that probably
involves viral assembly, possibly by interfering with
hemagglutinin processing.
-Inhibition of viral uncoating by:
a) Blockade of the viral membrane matrix protein M2,
which function as an ion channel.

6. This channel is required for the fusion of the viral
membrane with the cell membrane.
b) Rising the pH of the endosome (an acidic pH inside
endosome is required for viral uncoating) this induced
conformational changes in the hemagglutinin during its
intracellular transport at a later stage. The conformation
changes in hemagglutinin prevent transfer of the nascen
virus particles to the cell membrane for exocytosis.
Rimantadine is generally 4 to 10 times more active tha
amantadine.
Antiviral spectrum
-Influenza A virus (not B and C virus)

7. Neuraminidase inhibitors: Zanamivir and
Oseltamivir:
Protein coat of the influenza virus is a lipid envelo
Two macromolecules, surface glycoproteins,
embedded in the lipid envelope: hemagglutinin
neuraminidase. In order to spread in the body, the
virus first uses hemagglutinin, to bind to the healthy ce
receptors. Once it has inserted its RNA and replicated,
virus uses an enzyme, called neuraminidase, to sever
connection and move on to the next healthy cell.
Hemagglutinin is important for binding of the viru
the host cell membrane by a terminal sialic acid resid
Neuraminidase is an enzyme.

8. Nucleoside anti metabolites: Inhibiting viral
replication( Inhibitors of DNA Polymerase)
Ribavirin
Chemistry:
Ribavirin is 1-D-ribofuranosyl-1,2,thiazole-3carboxami
The compound is a purine nucleoside analog with a
modified base and a D-ribose sugar moiety.
:Mechanism of action
-The mechanism of action of ribavirin is not known. The
broad antiviral spectrum of ribavirin, however, suggests
multiple modes of action. The nucleoside is bioactivated
viral and host cellular kinases to give the monophosphate
(RMP) and the triphosphate (RTP).
.

9. Acyclovir and congeners
Chemistry
-Acyclovir, gancyclovir, famcyclovir, pemcyclovir all a
guanine nucleoside analogs.
Acyclovir, is the most effective of a series of acyclic
nucleosides that possess antiviral activity. In contrast wi
true nucleosides that have a ribose or a deoxyribose sug
attached to a purine or a pyrimidine base, the group
attached to the base in acyclovir is similar to an open
chain sugar, albeit lacking in hydroxyl groups
Mechanism of action
-All drugs are phosphorylated by a viral thymidine-kina
then metabolized by host cell kinases to nucleot
analogs.

10. Zidovudine
Chemistry
-Zidovudine is a thymine nucleoside analog
(deoxythymidine)
Mechanism of action
-The drug is phosphorylated by cellular thymidine kinase
the corresponding nucleotide analog
-The analog inhibits the RNA dependent DNA-polymeras
(inverse transcriptase) so blocking DNA synthesis(Rever
Transcriptase Inhibitors)
Zidovudine triphosphate competitively inhibits RT with
respect to thymidine triphosphate.

11. Other deoxynucleosides used in aids
Chemistry
-Didanosine is a purine deoxynucleoside .
-Zalcitabine and stavudine are pyrimidine
deoxynucleosides.
Mechanism of action
-The drug are phosphorylated by cellular kinases to th
corresponding nucleotide analogs.
-The analog inhibits the RNA dependent DNA-
polymerase (inverse transcriptase) so blocking DNA
synthesis is incorporated into viral DNA to cause chai
termination in HIV infected cells.

12. Non nucleoside Reverse Transcriptase
Inhibitors:
Unlike the nucleoside anti metabolites, the NNRTIs
not require bioactivation by kinases to yield phosph
esters.
They are not incorporated into the growing D
chain. Instead, they bind to an allosteric site that
distinct from the substrate (nucleoside triphospha
binding site of RT.
Such binding distorts the enzyme, so that it can
form the enzyme–substrate complex at its normal r
and once formed, the complex does not decompose at
normal rate to yield products.