Synthesis of Uracil and its Derivatives’ for Anticancer and Antiviral Drugs PREPARED BY ME \ ALI Yo

سودانيز اون لاين
سيف اليزل برعي البدوي-
مكتبتى
رابط مختصر

Authorized in 8/8/2015

بسم هللا الرحمن الرحيم

RESEARCH ABOUT

Synthesis of Uracil and

its Derivatives’ for

Anticancer and Antiviral

Drugs

PREPARED BY ME \

ALI YoUSIF HASAN

TEL: +249123760824

EMAIL:[email protected]

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TABLE OF CONTENTS

1. preface

2. introduction

3. proliferation of the cell

4. Mechanisms of Antineoplastic Drugs

5. classification of anticancer drugs

6. 5-uracil anticancer drug and its derivatives

7. Uracil derivatives as antiviral drugs

8. syntheses of uracil and 5-uracil

a. The Synthesis of uracil derivatives including 5U

b. The Synthesis of C5-Substituted Uracil

c. The Synthesis of N-Substituted Uracil

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Preface

This research about manufacturing of a drug always demanded

in our country, because it represents the chemotherapy witch comes

on the third degree of treatment of cancer dieses after surgical and

radiotherapy.

After a lot of investigations I found that the drug hasn't produces

in my country despite of the viability of raw materials uses in

production.so I decided to introduce this elaboration to enrich

Sudanese won pharmaceutics library

ALI YOUSIF

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Introduction

The body is made up of trillions of living cells. Normal body

cells grow, divide into new cells, and die in an orderly way.

During the early years of a person’s life when they are still growing,

normal cells divide faster. Once the person becomes an adult, most

cells divide only to replace worn-out, damaged, or dying cells.

Cancer begins when cells in a part of the body start to grow out of

control. There are, many kinds of cancer, but they all start by this outof-control

growth of abnormal cells. Cancer cell growth is different

from normal cell growth. Instead of dying, cancer cells keep on

growing and form new cancer cells. In most cases the cancer cells

form a tumor.

Cancer cells can also grow into (invade) other tissues, something that

normal cells can’t do. So being able to grow out of control and invade

other tissues are what makes every cell a cancerous.

Sometimes cancer cells spread to other parts of the body. There they

begin to grow and form new tumors. This process is called

####stasis.

No matter where a cancer spreads, it is named (and treated) based

on the place where it started. For instance, breast cancer that has

spread to the liver is still breast cancer not liver cancer. Likewise,

prostate cancer that has spread to the bones is still prostate cancer,

not bone cancer.

Different types of cancer can behave very differently. They grow at

different rates and respond to different treatments. That is why people

with cancer need treatment that is aimed at their own kind of cancer.

Not all tumors are cancerous. Tumors that aren’t cancer are

called benign. Benign tumors can cause problems – they can grow

large and press on healthy organs and tissues. But they can’t grow

into other tissues. Because of this, they also can’t spread to other

parts of the body (####stasize). These tumors are rarely life

threatening.

Proliferation of the cell

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Based on the DNA changes in cells, proliferating cycle of tumor

Cells can be divided into 5 phases

 Pre-synthetic phase (Gap 1 phase or G1 phase). Cells chiefly

make preparations for the synthesis of DNA.

 Synthetic phase (S phase). Cells are synthesizing their DNA.

 Post-synthetic phase (Gap 2 phase or G2 phase). DNA

Duplication has been finished and they are equally divided to

the two of future sub-cells.

 Mitosis phase (M Phase). Each cell is divided into two sub cells.

Some of these new cells enter the new proliferating cycle, the

others become non-proliferating cells.

 Some cell goes on non-proliferating cycle that G0 phase cells

Or (resting-phase cells), G0 phase cells have proliferation

ability but do not divide temporally.

When proliferating cells are suffered heavy casualties, G0

phase cells will get into proliferating cycle and become the reasons of

tumor recurrence. G0 phase cells are usually not sensitive to

antineoplastic drugs, which is the important obstacle to tumor

chemotherapy.

Mechanisms of Antineoplastic Drugs

Most antineoplastic drugs act on the proliferating cycle of cell:

(1) Destruction of DNA or inhibition of DNA duplication:

such as alkylating agents, Mitomycin C

(2) Inhibition of nucleic acid (DNA and RNA) synthesis

such as 5-fluorouracil, 6-mercaptopurine, methotrexate,

cytarabine, etc.

(3) Interfering with the transcription to inhibit RNA synthesis

such as dactinomycin, dauoruicin, and doxorubicin

(4) Inhibition of protein synthesis

such as vinca alkaloids, Epipodophylotoxins, and paclitaxel

(5) Interfering with hormone balance

such as adrenal corticosteroids, estrogens, tamoxifen etc.

Classification of anticancer drugs

There are five kind of anticancer drugs:-

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 Alkylating agents,

 Anti####bolites,

 Natural products,

 Hormones and antagonists

 Miscellaneous agents.

(Ⅰ) Alkylating Agents

Alkylating agents act via a reactive alkyl ethene (RCH2-CH2 +

-) group that reacts to form covalent bonds with nucleic acids.

There follows either cross-linking of the two strands of DNA,

preventing replication, or DNA breakage. All alkylating agents

are phase-nonspecific. Kill rapidly proliferating cells, also kill

nonproliferation cells.

 Examples: Mechlorethamine the first drug used in the treatment

of cancer. At present, it is mainly used for Hodgkin's disease

and non-Hodgkin's lymphomas.

 Examples: Cyclophosphamide Most widely used in clinical

therapy for treatment of cancer at present. It has no

antineoplastic action outside the body and must be activated in

the liver

(Ⅱ) Anti####bolites

Anti####bolites are analogues of normal ####bolites and act

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by competition, replacing the natural ####bolite and then

subverting cellular processes.

 Examples of anti####bolites include:

Folic acid antagonists (e.g. Methotrexate).

Antipyrimidines (e.g. 5-Fluorouracil, Cytarabine).

Antipurines (e.g. 6-Mercaptopurine)

 Example: methotrexate

Mimics folic acid, which is needed for synthesis of DNA, RNA

and some amino acids it acts mainly on the S phase cells. Side

effect a serious myelosuppression

 Example: 5-Fluorouracil (5-FU) a fluorine-substituted analogue

of uracil must be ####bolically activated to a nucleotide, in this

case FdUMP. Then its ####bolite inhibits the synthetase of

deoxythymidine monophosphate,blocking DNA synthesis.

Besides, as the fraudulent substance, its ####bolite can also

interfere with the synthesis of RNA.

 Example: 6-Mercaptopurine

A structural analogue of hypoxanthin It must be converted

intracellularly to the nucleotide 6-mercaptopurine ribose

phosphate and 6-methylmercaptopurine ribonucleotide, and

then inhibit purine biosynthesis, causing inhibition of

biosynthesis of nucleic acid.

(Ⅲ) Natural Products

This group is determined by the source of the drug

The major classes of natural products include antibiotics, vinca

alkaloids, biologic response modifiers enzymes,

epipodophyllotoxins and taxanes, Antibiotic antineoplastic

agents Damage DNA in cycling and noncycling cells.

 Example: Dactinomycin (actinomycin D)

This drug binds noncovalently to double-stranded DNA and

inhibits DNA-directed RNA syntheisis. Dactinomycin is a

phase-nonspecific agent, but it is more active agsinst G1

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phase cells.

 Vinca (plant) alkaloids Vincristine and vinblastine are

alkaloids derived from the periwinkle plant. binding to tubulin,

interfere with the assembly of spindle proteins during mitosis..

Act in (M) phase to inhibit mitosis, blocking proliferating cells as

they ####phase. Both can cause bone marrow suppression and

neurotoxicity

(Ⅳ) Hormones and antagonists

The growth of some cancers is hormone dependent. Growth

of such cancers can be inhibited by surgical removal of

hormone glands increasingly, however, administration of

hormones or anti hormones is preferred.

Examples:

Adrenocortical steroids to inhibit the growth of cancers of

lymphoid tissue and blood. Estrogen antagonists (Tamoxifen)

are indicated for breast cancer. Estrogen is used for prostatic

cancers.

(Ⅴ) Miscellaneous agents

Examples: Hydroxyurea

Hydroxyurea inhibits ribonucleotide reductase. Inhibition of

DNA synthesis. It is specific for the cells of S phase .The major

adverse effect of this drug is bone marrow depression.

5-uracil anticancer drug and it derivatives

Mechanism of action

Pyrimidine Drugs

The anticancer drugs based on pyrimidine structure the

pyrimidine derivative 5-fluorouracil (5-FU) was designed to block the

conversion of Uridine to thymidine. The normal biosynthesis of

thymidine involves methylation of the 5-position of the pyrimidine ring

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of uridine. The replacement of the hydrogen at the 5-position of uracil

with a fluorine results in an anti####bolite drug, leading to the

formation of a stable covalent ternary complex composed of 5-FU,

thymidylate synthase (TS), and cofactor (a tetrahydrofolate species).

The normal pathway for the formation of thymidine from uridine

catalyzed by the enzyme TS is shown in Scheme below (No 1).

Anticancer drugs targeting this enzyme should selectively inhibit the

formation of DNA because thymidine is not a normal component of

RNA. TS is responsible for the reductive methylation of deoxyuridine

monophosphate (dUMP) by 5,10-methylenetetrahydrofolate to yield

dTMP and dihydrofolate. Because thymine is unique to DNA, the TS

enzyme system plays an important role in replication and cell division.

The tetrahydrofolate cofactor species serves as both the one-carbon

donor and the hydride source in this system. The initial step of the

process involves the nucleophilic attack by a sulfhydryl group of a

cystine residue at the 6-position of dUMP. The resulting enolate adds

to the methylene of 5,10- CH2-THF perhaps activated via the very

reactive N-5- iminium ion (see Scheme below(1)). The iminium ion

likely forms at N-5 and only after 5,10-CH2-THF binds to TS. The

The chemical mechanism of inhibition of Thymidylate synthetase by

5-fluorouracil is shown in Scheme 2. This process clearly shows that

in order to inactivate the TS enzyme, both 5-FU and the

tetrahydrofolate species are required to form the ternary complex.

Some clinical studies have shown that administration of a

tetrahydrofolate source prior to treatment with 5-FU results in greater

inhibition of total TS activity. The administered source of active 5,10-

methylenetetrahydrofolate is leucovorin, N-5-formyltetrahydrofolate.

TS is the most obvious and well-documented mechanism of action for

5-FU cytotoxic activity. However, other mechanisms may play a role

in the overall value of this drug in the treatment of human cancer. The

triphosphate of 5-FU nucleotide is a substrate for RNA polymerases,

and 5-FU is incorporated into the RNA of some cell lines. The

incorporation of 5-FU into DNA via DNA polymerase occurs in some

tissue lines even though uracil is not a common component of human

DNA. The 5-FU in DNA likely serves as substrate for the editing and

repair enzymes involved in DNA processing for cell division and

tissue growth. The actual addition of 5-FU into RNA and/or DNA may

not be the direct cytotoxic event, but the incorporation may lead to

less efficient utilization of cellular resources. The significance of these

various mechanisms on the overall cytotoxic effects of 5-FU may vary

with cell line and tissue.

The ####bolic activation (anabolism) of 5-FU required to

produce the anticancer effects accounts for no more than 20% of the

administered amount of drug in most patients. Catabolic inactivation

via the normal pathways for uracil consumes the remaining

approximate 80% of the dose. The major enzyme of pyrimidine

catabolism is dihydropyrimidine dehydrogenase (DPD), and 5-FU is a

substrate for this enzyme. The DPD catabolism of 5-FU is shown in

Scheme. The formation of dihydro-5-FU (5-FU-H2) occurs very

rapidly and accounts for the majority of the total 5-FU dose in most

patients. Thus, _-fluoro-_-alanine is the major human ####bolite of 5-

FU. Uracil is a substrate for this enzyme system also and has been

dosed with 5-FU and 5-FU prodrugs in an attempt to saturate DPD

and conserve active drug species. Variability in the levels of DPD

activity among the patient population is a major factor in the

bioavailability of 5-FU. Inhibitors of DPD such as uracil or 5-chloro-

2,4- dihydroxypyridine (CDHP) increase the plasma concentration–

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time curve of 5-FU by preventing 5-FU catabolism. One mechanism

of drug resistance in 5-FU–treated patients may be caused by

increased levels of DPD in the target tissue. The observed low

bioavailability of 5-FU as a result of the catabolic efficiency of DPD

and other enzymes has led to the development of unique dosing

routes and schedules as well as the development of prodrug forms of

5-FU. Attempts at chemical modification of 5-FU to protect from

catabolic events have produced several prodrug forms, which are

converted via in vivo ####bolic and/or chemical transformation to the

parent drug 5-FU. The carbamate derivative of 5_-deoxy-5-

fluorocytidine is known as capecitabine, and it is converted to 5-FU

through a series of activation steps. The activation sequence is

shown in Scheme3. The initial step is carbamate hydrolysis followed

by deamination, then hydrolysis of the sugar moiety to yield 5-FU.

Some of these activation steps take place at a higher rate in tumor

tissue leading to selective accumulation in those cells. The last step

in the sequence is catalyzed by phosphorolases, and these enzymes

occur in higher levels in colorectal tumors. Despite this complex

activation process, capecitabine still exhibits some of the significant

toxicities of 5-fluorouracil. The tetrahydrofuran derivative tegafur is

slowly converted to 5-FU but requires quite high doses to reach

therapeutic plasma concentrations. Esters of the N-hydroxymethyl

derivative of tegafur show greater anticancer activity than tegafur.

Pyrimidine analogs as anti####bolites for cancer therapy have been

developed based on the cytosine structure as well. Modification of the

normal ribose or deoxyribose moiety has produced useful drug

species such as cytarabine (ara-C) and gemcitabine, Cytosine

arabinoside (ara-C or cytarabine) is simply the arabinose sugar

instead of ribose, and the only difference in structure is the epimeric

hydroxyl group at the 2_-position of the pentose sugar. This epimeric

sugar is similar enough to the natural ribose to allow ara-C to be

incorporated into DNA, and its mechanism of action may include a

slowing of the DNA chain elongation reaction via DNA polymerase or

cellular inefficiencies in DNA processing or repair after incorporation.

Gemcitabine is the result of fluorination of the 2_-position of the sugar

moiety. Gemcitabine is the 2_,2_-difluoro deoxycytidine species and

after its anabolism to diphosphate and triphosphate ####bolites, it

inhibits ribonucleotide reductase and competes with 2_-deoxycytidine

triphosphate for incorporation into DNA. The mechanism of action for

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gemcitabine is likely similar to that of ara-C including alteration of the

rate of incorporation into DNA as well as the rate of DNA processing

and repair. Modification of the pyrimidine ring has also been explored

for the development of potential anticancer drugs based on

anti####bolite theory. Several pyrimidine nucleoside analogs have

one more or one less nitrogen in the heterocyclic ring. They are

known as azapyrimidine or deazapyrimidine nucleosides. 5-

Azacytidine is an example of a drug in this category (see Fig. 3). This

compound was developed via organic synthesis and later found as a

natural product of fungal ####bolism. The mode of action of this

compound is complex involving reversible inhibition of DNA

methyltransferase, and this lack of methylated DNA activates tumor

suppressor genes. In certain tumor systems, it is incorporated into

nucleic acids, which may result in misreading or processing errors.

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What is 5-flourouracil؟

fluoro-1H, 3H -pyrimidine-2, 4-dione

This chemical product has wourld wide trade marks drugs as fellow:-

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5-FLUOROURACIL (5-FU, EFUDEX, ADRUCIL,

FLUOROPLEX)

The drug is available in a 500-mg or 10-mL vial for IV use and

as a 1% and 5% topical cream. 5-FU is used in the treatment of

several carcinoma types including breast cancer, colorectal cancer,

stomach cancer, pancreatic cancer, and topical use in basal cell

cancer of the skin. The mechanism of action includes inhibition of the

enzyme TS by the deoxyribose monophosphate ####bolite, 5-

FdUMP. The triphosphate ####bolite is incorporated into DNA and

the ribose triphosphate into RNA. These incorporations into growing

chains result in inhibition of synthesis and function of DNA and RNA.

Resistance can occur as a result of increased expression of TS,

decreased levels of reduced folate substrate 5,10

methylenetetrahydrofolate, or increased levels of dihydropyrimidine

dehydrogenase. Dihydropyrimidine dehydrogenase is the main

enzyme responsible for 5-FU catabolism. Bioavailability following oral

absorption is erratic. Administration of 5-FU by IV yields high drug

concentrations in bone marrow and liver. The drug does distribute

into the central nervous system (CNS). Significant drug interactions

include enhanced toxicity and antitumor activity of 5-FU following

pretreatment with leucovorin. Toxicities include dose-limiting

myelosuppression, mucositis, diarrhea, and hand–foot syndrome

(numbness, pain, erythema, dryness, rash, swelling, increased

pigmentation, nail changes, pruritus of the hands and feet).

CAPECITABINE (XELODA)

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The drug is available in 100-, 500-, 1,000-, and 2,000-mg multi doses

vials for IV use. Cytarabine is used in the treatment of acute

myelogenous leukemia and CML. This drug is a deoxycytidine analog

originally isolated from the sponge Cryptothethya crypta. It is active

following intracellular activation to the nucleotide ####bolite ara-CTP.

The resulting ara-CTP is incorporated into DNA resulting in chain

termination and inhibition of DNA synthesis and function. Resistance

can occur because of decreased activation or transport and

increased catabolic breakdown. ####bolic breakdown within the GI

tract leads to poor bioavailability. The drug distributes rapidly into

tissues and total body water with cerebrospinal fluid (CSF) levels

reaching 20% to 40% of those in plasma. Cytidine deaminase is the

primary catabolic enzyme involved in the inactivation of cytarabine.

Drug interactions include antagonism of the effects of gentamicin,

decreasing the oral bioavailability of digoxin, as well as enhancing the

cytotoxicity of various alkylating agents, cisplatin, and ionizing

radiation. Pretreatment with methotrexate enhances the formation of

ara-CTP ####bolites resulting in enhanced cytotoxicity. Toxicities

include myelosuppression, leukopenia and thrombocytopenia,

nausea and vomiting anorexia, diarrhea, and mucositis. Neurotoxicity

is usually expressed as ataxia, lethargy, and confusion. An allergic

reaction often described in pediatric patients includes fever, myalgia,

malaise, bone pain, skin rash, conjunctivitis, and chest pain.

FLOXURIDINE (FLUORODEOXYURIDINE, FUDR)

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The drug is available as a 500-mg vial of lyophilized powder.

The drug is used to treat ####static GI adenocarcinoma. The

mechanism of action of this fluoropyrimidine deoxynucleoside analog

involves ####bolic conversion to 5-fluorouracil (5-FU) ####bolites

resulting in inhibition of TS thus disrupting DNA synthesis, function,

and repair. Resistance can occur because of increased expression of

TS, decreased levels of reduced folate 5,10-

methylenetetrahydrofolate, increased activity of DNA repair enzymes,

and increased expression of dihydropyrimidine dehydrogenase (the

major catabolic enzyme). The drug is poorly absorbed from the GI

tract and is extensive ####bolized to 5-FU and 5-FU ####bolites.

Dihydropyrimidine dehydrogenase is the main enzyme responsible

for 5-FU catabolism, and it is present in liver, GI mucosa, white blood

cells, and kidney. The drug interaction and toxicity profiles are

#####alent to those of 5-FU.

GEMCITABINE (DFDC, GEMZAR)

The drug is available as the hydrochloride salt in 200- and

1,000-mg lyophilized single-dose vials for IV use. Gemcitabine is

used to treat bladder cancer, breast cancer, pancreatic cancer, and

NSCLC. Gemcitabine is a potent radio sensitizer, and it increases the

cytotoxicity of cisplatin. The mechanism of action of this fluorinesubstituted

deoxycytidine analog involves inhibition of DNA synthesis

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and function via DNA chain termination. The triphosphate ####bolite

is incorporated into DNA inhibiting several DNA polymerases and

incorporated into RNA inhibiting proper function of mRNA. Resistance

can occur because of decreased expression of the activation enzyme

deoxycytidine kinase or decreased drug transport as well as

increased expression of catabolic enzymes. Drug oral bioavailability

is low because of deamination within the GI tract, and the drug does

not cross the blood-brain barrier. ####bolism by deamination to 2_,

2_ difluorouridine (dFdU) is extensive. Drug toxicity includes

myelosuppression, fever, malaise, chills, headache, myalgia, nausea,

and vomiting.

Uracil uses as Antiviral Drugs

Inhibitors of DNA polymerase

Idoxuridine

Idoxuridine, 5-iodo-2_deoxyuridine (Stoxil, Herplex)

This drug was introduced in 1963 for the treatment of herpes simplex

keratitis. The drug is an iodinated analog of thymidine that inhibits

replication of several DNA viruses in vitro. The susceptible viruses

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include the herpes viruses and poxviruses (vaccinia). The mechanism

of action of Idoxuridine has not been completely defined, but several

steps are involved in the activation of the drug. Idoxuridine enters the

cell and is phosphorylated at O-5 by a viral thymidylate kinase to yield

a monophosphate, which undergoes further biotransformation to a

triphosphate. The triphosphate is believed to be both a substrate and

an inhibitor of viral DNA polymerase, causing inhibition of viral DNA

synthesis and facilitating the synthesis of DNA that contains the

iodinated pyrimidine. The altered DNA is more susceptible to strand

breakage and leads to faulty transcription. When the iodinated

DNA is transcribed, the results are miscoding errors in RNA and

faulty protein synthesis. The ability of idoxuridylic acid to substitute for

deoxythymidylic acid in the synthesis of DNA may be a result of the

similar van der Waals radii of iodine (2.15 Å) and the thymidine

methyl group (2.00 Å). In the United States, Idoxuridine is approved

only for the topical treatment of herpes simplex virus (HSV) keratitis;

although outside the United States, a solution of Idoxuridine in

dimethyl sulfoxide is available for the treatment of herpes labialis,

genitalis, and zoster. The use of Idoxuridine is limited because the

drug lacks selectivity; low, sub therapeutic concentrations inhibit the

growth of uninfected host cells. The effective concentration of

Idoxuridine is at least 10 times greater than that of acyclovir.

Idoxuridine occurs as a pale yellow, crystalline solid that is soluble in

water and alcohol but poorly soluble in most organic solvents. The

compound is a weak acid, with a pKa of 8.25. Aqueous solutions are

slightly acidic, yielding a pH of about 6.0. Idoxuridine is light and heat

sensitive. It is supplied as a 0.1% ophthalmic solution and a 0.5%

ophthalmic ointment.

Cytarabine

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This drug is mentioned above.

Trifluridine

Trifluridine, 5-trifluoromethyl-29-deoxyuridine (Viroptic),

Is a fluorinated pyrimidine nucleoside that demonstrates in vitro

inhibitory activity against HSV-1 and HSV-2, CMV, vaccinia, and

some adenoviruses. Trifluridine possesses a trifluoromethyl group

instead of an iodine atom at the 5-position of the pyrimidine ring. The

van der Waals radius of the trifluoromethyl group is 2.44 Å, somewhat

larger than that of the iodine atom. Like Idoxuridine, the antiviral

mechanism of Trifluridine involves inhibition of viral DNA synthesis.

Trifluridine monophosphate is an irreversible inhibitor of thymidylate

synthetase, and the biologically generated triphosphate competitively

inhibits thymidine triphosphate incorporation into DNA by DNA

polymerase. In addition, Trifluridine in its triphosphate form is

incorporated into viral and cellular DNA, creating fragile, poorly

functioning DNA. Trifluridine is approved in the United States for the

treatment of primary keratoconjunctivitis and recurrent epithelial

keratitis caused by HSV types 1 and 2. Topical Trifluridine shows

some efficacy in patients with acyclovir-resistant HSV cutaneous

infections. Trifluridine solutions are heat sensitive and require

refrigeration.

Cidofovir

Cidofovir, (S)-3-hydroxy-2-phosphonomethoxypropyl cytosine

(HPMPC, Vistide)

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Is an acyclonucleotide analog that possesses broad-spectrum

activity against several DNA viruses. Unlike other nucleotide analogs

that are activated to nucleoside phosphates, Cidofovir is a

phosphonic acid derivative. The phosphonic acid is not hydrolyzed by

phosphatases in vivo but is phosphorylated by cellular kinases to

yield a diphosphate. The diphosphate acts as an anti####bolite to

deoxycytosine triphosphate (dCTP). Cidofovir diphosphate is a

competitive inhibitor of viral DNA polymerase and can be

incorporated into the growing viral DNA strand, causing DNA chain

termination. Cidofovir possesses a high therapeutic index against

CMV and has been approved for treating CMV retinitis in patients

with AIDS. Cidofovir is administered by slow, constant intravenous

infusion in a dose of 5 mg/kg over a 1-hour period once a week for 2

weeks. This treatment is followed by a maintenance dose every 2

weeks. About 80% of a dose of Cidofovir is excreted unchanged in

the urine, with a t1/2elim of 2 to 3 hours. The diphosphate

anti####bolite, in contrast, has an extremely long half-life (17–30

hours). The main dose-limiting toxicity of Cidofovir involves renal

impairment. Renal function must be monitored closely. Pretreatment

with probenecid and prehydration with intravenous normal saline can

be used to reduce the nephrotoxicity of the drug. Patients must be

advised that Cidofovir is not a cure for CMV retinitis. The disease

may progress during or following treatment.

Zidovudine

Zidovudine, 3_-azido-3_-deoxythymidine or AZT .

Is an analog of thymidine that possesses antiviral activity against

HIV-1, HIV-2, HTLV-1, and several other retroviruses. This

nucleoside was synthesized in 1978 by Lin and Prusoff47 as an

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liver. Only about 15% is excreted unchanged. Because AZT is an

aliphatic azide, it is heat and light sensitive. It should be protected

from light and stored at 15°C to 25°C.

Zalcitabine

Zalcitabine, 2_ 3_-dideoxycytidine or ddCyd,

Is an analog of cytosine that demonstrates activity against HIV-1 and

HIV-2, including strains resistant to AZT. The potency (in peripheral

blood mononuclear cells) is similar to that of AZT, but the drug is

more active in populations of monocytes and macrophages as well as

in resting cells. Zalcitabine enters human cells by carrier-facilitated

diffusion and undergoes initial phosphorylation by deoxycytidine

kinase. The monophosphorylated compound is further ####bolized to

the active ####bolite, dideoxycytidine-5_- triphosphate (ddCTP), by

cellular kinases. ddCTP inhibits RT by competitive inhibition with

dCTP. Most likely, ddCTP causes termination of the elongating viral

DNA chain. Zalcitabine inhibits host mitochondrial DNA synthesis at

low concentrations. This effect may contribute to its clinical toxicity.

The oral bioavailability of Zalcitabine is over 80% in adults and less in

children. The major dose-limiting side effect is peripheral neuropathy,

characterized by pain, paresthesias, and hypesthesia, beginning in

the distal lower extremities. These side effects are typically evident

after several months of therapy with Zalcitabine. A potentially fatal

pancreatitis is another toxic effect of treatment with ddC. The drug

has been approved for the treatment of HIV infection in adults with

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advanced disease who are intolerant to AZT or who have disease

progression while receiving AZT. ddC is combined with AZT for the

treatment of advanced HIV infection.

Stavudine

2_3_-didehydro-2_-deoxythymidine (D4T, Zerit) .

It’s an unsaturated pyrimidine nucleoside that is related to thymidine

The drug inhibits the replication of HIV by a mechanism similar to that

of its close congener AZT. Stavudine is bio activated by cellular

enzymes to a triphosphate. The triphosphate competitively inhibits

the incorporation of thymidine triphosphate (TTP) into retroviral DNA

by RT. Stavudine also causes termination of viral DNA elongation

through its incorporation into DNA. Stavudine is available as capsules

for oral administration. The drug is acid stable and well absorbed

(about 90%) following oral administration. Stavudine has a short halflife

(1–2 hours) in plasma and is excreted largely unchanged (85%–

90%) in the urine. As with ddC, the primary dose limiting effect is

peripheral neuropathy. At the recommended dosages, approximately

15% to 20% of patients experience symptoms of peripheral

neuropathy. Stavudine is recommended for the treatment of adults

with advanced HIV infection who are intolerant of other approved

therapies or who have experienced clinical or immunological

deterioration while receiving these therapies.

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Synthesis of uracil and 5-uracil

There are five worldwide methods since 1901 to produce Uracil and

5-uracil but unfortunately no one had used in Sudan

Fischer and Roeder’s Synthesis:

The first successful laboratory synthesis of uracil was achieved

by Fischer and Roeder in 1901. Their synthesis involved the

condensation of urea and ethyl acrylate into dihydrouracil, followed by

bromination and debromination with alkali . Unfortunately, Fischer

and Roeder’s synthesis of uracils generally results in low yields.

Wheeler and Liddle’s Synthesis:

In Wheeler and Liddle’s synthesis, urea or thiourea is reacted

with a ketoester. When thiourea is used, the resulting sulfurcontaining

product must be subsequently heated in aqueous acid to

afford the desired uracil

Wheeler and Liddle’s synthesis is moderately yielding and quite

versatile, making it one of the more commonly used techniques for

the synthesis of uracils.

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Davidson-Baudisch Synthesis:

The Davidson-Baudisch synthesis of uracil is a simple one-pot

method involving the treatment of urea and malic acid with fuming

sulfuric acid:

The Davidson-Baudisch synthesis is facile and can afford various

uracils in moderate yields.

Bergmann Synthesis:

In the Bergmann synthesis, a substituted cyanoacetic acid is

condensed with urea in the presence of acetic anhydride and

subsequently reduced by catalytic hydrogenation. Reactions of this

type generally proceed in moderate yield and, unlike many of the

aforementioned syntheses, do not require harsh conditions or the

removal of sulfur.

.

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halosuccinimides

This reaction can be achieved by a number of reagents, including

fluoromethyl hypofluorite (FCH2OF) cesium fluoroxysulfat (CsSO4F)

fluoroxytrifluoromethane (CF3OF) and acetyl hypofluorite

(CH3COOF).

5-Nitrouracil is most often synthesized by the direct C5-nitration

of uracil. This can be accomplished using reagents such as nitric acid

and sulfuric acid palladium(II) acetate and sodium nitrite copper(II)

nitrate and acetic anhydride and nitronium tetrafluoroborate

(NO2BF4).

Lastly, 5-(trifluoromethyl)uracil can be prepared by several methods,

including the direct C5-trifluoromethylation of uracil with aqueous

bis(trifluoromethyl) mercury in the presence of azoisobutyronitril

(AIBN). Unfortunately, this synthesis suffers from multiple

disadvantages such as low yields and the use of highly toxic

reagents. The superior synthesis of 5-(trifluoromethyl)uracil involves

the chlorination of thymine, first with phosphorus oxychloride in the

presence of a tertiary amine and then with elemental chlorine,

followed by fluorination with hydrogen fluoride and subsequent

hydrolysis using aqueous potassium or sodium fluoride. This method

is quite high yielding and used prominently in industry:

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The Synthesis of N-Substituted Uracils

The synthesis of N-substituted uracil analogues can also be

carried out through various methods of uracil ring formation if

appropriate starting materials, such as N-substituted urea or thiourea,

are used. However, it is difficult to achieve regioselectivity in this

fashion.

A more practical approach to N-substituted uracil analogue synthesis

is the direct N1 and/or N3-alkylation of uracils. It is believed that N1-H

of uracil is more acidic than N3-H, indicating that substitutions

involving the use of base and various alkyl halides should proceed

more readily at N1. While this is true in some cases, a mixture of N1

and N3 mono- and di substituted uracil products is often obtained.

The ratio between these three products is highly dependent on the

reaction conditions, the #####alents of substituting reagents used,

and the substituents already present on the starting uracil N1- or N3-

specific substitutions can be made more favorable by employing

uracil protecting groups (UPGs). An ideal UPG would be one that

directs alkylation completely to either N1 or N3, is stable enough to

withstand the substitution reaction conditions, and is labile enough to

be removed without difficulty after reaction completion. Many existing

UPGs are limited due to poor N-selectivity or harsh deprotection

steps, but an acceptable level of success has been achieved through

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the methods reviewed below.

N1-Directed Uracil Substitution:

The substitution of uracils at N1 can be facilitated by the direct

protection of N3, although UPGs that exclusively react with N3 are

uncommon. However, the N3- protection of some uracils can be

achieved indirectly. For example, when uracil is reacted with excess

benzoyl chloride, the N1,N3-dibenzoylated products initially obtained

can be quickly decomposed to their monosubstituted 3-benzoyl

derivatives via mildly basic conditions or chromatography on alumina

Alternatively, N1-substitution can be made more favorable through

the steric hindrance of N3-substitution. This can be accomplished by

protecting the uracil oxygen with bulky functionalities, such as the

trimethylsilyl group (figure 15). Bis(trimethylsilyl) acetamide (BSA) or

hexamethyldisilazane (HMDS) and trimethylsilyl chloride (TMSCl) can

be used for the trimethylsilylation of uracils.

N3-Directed Uracil Substitution:

N3-substitution is primarily facilitated through the direct

protection of N1, A number of UPGs have been successfully used for

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the N1-protection of uracils, including the benzhydryl, 2-(trimethylsilyl)

ethoxymethyl (SEM), benzyl, benzyloxymethyl (BOM),

methylthiomethyl (MTM), and p-methoxybenzyl (PMB)

groups

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