pf3002 lab manual

COLÁISTE NA hOLLSCOILE CORCAIGH UNIVERSITY COLLEGE CORK

PF3002

Pharmaceutical Chemistry III

Practical Manual

School of Pharmacy

Contents

Health Warning 3

Introduction and general information 4

Safety 6

Practical reports 9

Laboratory sessions

1. Synthesis of 5,5-diphenylhydantoin (Phenytoin) 10

2. Preparation of Nitrazepam 12

Chemistry Practical Health Warning Checklist Read the manual before stepping inside the laboratory

Read the safety precautions and emergency procedures before using any

chemical

Always wear protective measures appropriate to the risk situation

Read data sheet before initiating any work and complete risk assessment

Assess the situation in front of you before starting your procedure

The laboratory is a shared facility – be aware of your own and your

neighbours safety

Communicate, communicate, communicate

Consult your demonstrator if unsure of anything

Remember you will be marked on laboratory efficiency not speed

This list is intended to ensure your safety. It is not a comprehensive list of the safety aspects required for this series

Introduction Pharmaceutical chemistry seeks to examine the synthetic methodology used in order to

produce pure biologically active molecules to be formulated as medicines.

An in depth understanding of organic chemistry is core to the study of this subject as it

plays a key role in many of the processes utilised in the formation of medicines. PF3002

builds on the core knowledge attained in PF1001, PF2001 and PF2002 and applies this to

the pharmaceutical process. Key to this is the manipulation and transformation of

functional groups in a structured manner to produce a suitable end product. With this

knowledge, known functional group chemistry will be applied to the formation of new

medicines.

An important factor in pharmaceutical chemistry is the adaptability of the chemistry in

the initial stages of a project in order to achieve analogues and derivatives of a lead

compound, and in the final stages the ability to take a laboratory scale process (medicinal

chemistry route producing milligrams of product for biological testing) and reproduce the

same compound on a plant scale (producing kilos of product for formulation and market).

This course will give an insight into the problems faced by all pharmaceutical companies

producing compounds for use as medicines and the industrialisation of chemistry. As will

be seen the medicinal chemistry route to most products is usually adapted and changed

completely as the project progresses.

In this series of labs we will learn about the issues concerning pharmaceutical production

from drug discovery to plant scale manufacture. This practical series on the design and

synthesis of compounds for medical use requires familiarity with the practical aspects of

organic chemistry and for this it is important you revise the practical issues learned in

PF1001 and PF2001, at least for safety reasons if not for academic. It must also be noted

that most of the compounds and chemicals used will be bio-active to some degree (as that

is the purpose of the chemistry) and so must be handled with caution and care.

There are two practical experiments to be completed over four weeks that are designed to

enhance your chemical skills to the level required to manipulate organic compounds in

the very first process of pharmaceutical production. The initial chemistry involved will be

familiar from lectures however it is essential to read thoroughly the experimental

instructions involved in each laboratory session.

The following experiments will be carried out:

• Experiment 1: Synthesis of 5,5-diphenylhydantoin (Phenytoin)

• Experiment 2: Preparation of Nitrazepam

GENERAL INFORMATION

It is essential that you familiarise yourself with each practical before attending a laboratory session.

The following MUST be brought to ALL pharmaceutical chemistry laboratory practicals:

• Laboratory coat and safety glasses

• Laboratory manual (this book)

• Small hardback notebook labelled with your name, course and student ID number. This

will be used as your own record of the experiment

• Calculator

• J-Cloth or tissues to clean the bench

Each laboratory session begins with a brief talk from the laboratory instructor in which

the experiment will be described and advice on the correct procedure given.

You must be on time for all laboratory sessions. An attendance record is taken. GENERAL RULES: 1. Admission to the laboratory is not permitted without safety glasses or laboratory

coat.

2. Bags should not be brought into the laboratory or left in the corridor outside the

labs. Use your locker.

3. No food or drink is to be brought into the laboratory

4. Always read all the safety notes for each experiment.

5. Do not take off your safety spectacles or laboratory coat at any time.

6. Keep your bench tidy and avoid spilling chemicals.

7. Do not swallow or touch any chemicals.

8. Consult your Demonstrator before attempting any technique which is unfamiliar.

Remember: There are many potential hazards in the laboratory.

It is you and your colleagues that are at risk.

Be careful and insist that your co-workers are just as careful.

Safety in Laboratory Classes

When in the laboratory it is essential that you observe all the regulations for your own

safety and for that of your colleagues.

SAFETY SPECTACLES MUST BE WORN AT ALL TIMES, FAILURE TO DO SO WILL RESULT IN YOUR REMOVAL FROM THE LABORATORY. EATING, DRINKING and SMOKING ARE ALL FORBIDDEN.

You should only carry out practical work when a demonstrator is present. No bench

work is permitted outside the set laboratory periods for safety reasons.

Some of the products that you will be making are bio-active, and therefore MUST be

handled with care to avoid contact either by inhalation, ingestion or through skin contact.

Bio-active compounds will cause varying effects on people and it must be stressed that on

no circumstances should any product or reagent come in contact with your person. Treat

all compounds with respect, and ensure spillages are dealt with by either a technician or

demonstrator.

Most organic solvents are highly flammable (especially diethyl ether), and the use of

naked flames (bunsen burners) nearby or in the same fume cupboard is forbidden.

ALWAYS check what your neighbour is doing. All chemicals should be handled with

care, but some are particularly hazardous. These should be handled in the fume cupboard

and the appropriate glove/additional protective clothing should be worn. Avoid breathing

vapours of any volatile organic compound. Check the data sheets before using any

organic material and know the emergency procedures involved.

The laboratory is a communal area and so benches must be left clean and tidy and

apparatus such as balances and rotary evaporators must not be left in a dirty condition.

Always clean up your own mess before you move on to the next stage of any procedure.

It is not fair to expect someone else to clear up your mess. Not only is this good practice

but it is an essential safety requirement.

Before you start any practical you are required to carry out a risk assessment of ALL the

compounds, reagents and solvents you will be using listing their hazards. This should be

written at the start of each experiment (incorporated into the data sheets). A typical

assessment is given below. Remember, that safety should always come first and if you

are in any doubt, ASK a demonstrator. They are there to help you.

Sample Assessment: Chemical Approx. amount Assessment Hazards Spillage

Acetylacetone

Sodium

hydroxide

Toluene

Petroleum

6g

5M soln

20 ml

75 ml

standard

standard

fume

cupboard

standard

toxic

corrosive

toxic

corrosive

flammable

flammable

wash with

water

wash with

water

see

demonstrator

see

demonstrator

IN THE EVENT OF AN ACCIDENT IN THE LABORATORY, NOTIFY THE DEMONSTRATORS, TECHNICIANS OR ACADEMIC STAFF IMMEDIATELY

Data Sheets, Notebook, Practical Reports and Seminars

This practical series contains 4 component marks: a laboratory efficiency mark, a data

sheet mark, a practical report mark and a seminar mark.

The hardback notebook you are required to have is for your own records. It is important

that you keep a detailed laboratory notebook in which you should write down exactly

what you have done and record any observations. This will be vital for future use and

revision. It is also good laboratory practice and should be updated as the reaction

proceeds, not completed when finished. All observations and results should be entered

directly into your laboratory notebook.

The efficiency mark is given for competency and cleanliness. Please note this mark is not

time dependent – faster does not mean better. The mark is based on the quality of your

work. A well completed laboratory notebook is a good indicator of efficiency.

A complete data sheet is required for each experiment. Details on the data sheet will

include overall reaction equations, melting points, yields, relevant analysis, etc. This

sheet must be signed by your demonstrator before you leave the laboratory.

On completion of the practical, a practical report must be drawn up and handed to your

demonstrator by the deadline given (usually 1 week after the practical has been

completed). The report should consist of the following sections:

Title of Experiment Date Introduction Detail briefly the objectives of the experiment (max half page A4)

Safety Assessment Assessment of all reagents and solvents

Experimental Procedure Insert reference to manual. Do not transcribe from the manual. Include details of any

procedures that are different from those given in the laboratory manual only.

Reaction details If not on data sheet: weights, equivalents and number of moles of starting materials and

reaction equation.

Results If not on data sheet, report the results clearly and in tabular form when appropriate.

Weights and percentage yield(s) of product(s) along with their melting point and spectra

required. No need to copy from data sheet.

Discussion Outline the significance of your results. Provide concluding remarks and answer

all questions given in the manual (max 2 page A4). Include mechanisms for the reactions in the experiments where appropriate, along with

the interpretation of NMR/IR spectra and the answers to any questions that are required.

ALL your products should be handed in, in a clearly labelled sample tube (Your

name, experiment number and structure).

Report should be submitted in a plastic A4 sheet including the signed data sheet. These

reports will be returned for review and feedback after marking but will be recollected at

end of practical series. Final practical mark will be determined by return of reports.

If you are unsure about any technique or instruction given in the experimental script,

ASK THE DEMONSTRATOR. A number of videos are available in the laboratory,

which show the basic techniques you will need to use. Work should be presented for

marking as soon as the experiment is completed.

Seminar marks will be determined on presentation, content and delivery. Seminars will

take place during laboratory time and topics will be assigned in the first week of

practicals.

Experiment 1 Synthesis of 5,5-diphenylhydantoin (Phenytoin)

Introduction Phenytoin has been widely prescribed for the control of epilepsy since its introduction as

a pharmaceutical agent during 1950’s, and although superseded by a number of newer

drugs, it remains in use today in this role. The main structural challenge for the synthesis

of this compound is the construction of the hydantoin ring. This hydantoin ring can be

formed in a one-pot procedure starting from benzil. The procedure for this reaction is a

base catalysed addition of urea to benzil that is an interesting example of a benzilic acid

re-arrangement where the phenyl groups undergoes a 1,2-migration during formation of

the hydantoin ring (Scheme 1).

O

O KOH, NH2CONH2

Ethanol HNNH

O

O Scheme 1 Synthesis of phenytoin from benzil

Objectives Synthesis and purification of a pharmaceutical product and confirmation of purity by

melting point, TLC and IR analysis.

Materials Benzil 2g Irritant

Urea 780 mg Irritant

Potassium Hydroxide 2 g Harmful / Corrosive

Hydrochloric Acid Harmful / Corrosive

Ethanol 80 ml Harmful

Procedure

Benzil (2.00 g, 10 mmol), potassium hydroxide (2.00 g, 17.82 mmol) and urea (780 mg,

13 mmol) were dissolved in dry ethanol (80 ml) and heated gently to reflux on a steam

bath until TLC analysis [ethyl acetate:hexane (20:80)] indicated complete consumption

of starting material. The reaction mixture is then poured onto an ice/water mixture (100

ml) and the solution filtered to remove a small quantity of 4,5-diphenyl-4.5-dihydroxy-2-

imidazolone. The remaining red solution is acidified by the drop wise addition of

concentrated hydrochloric acid (CARE) to precipitate the product as a white solid, which

was removed by filtration, washed with water and dried to give the product that is

recrystallised from ethanol. You should calculate the yield of recrystallised material, and

record the IR and melting point of your product.

Questions The most common method for the synthesis of phenytoin analogues is the Bergs

synthesis which has been previously been used to prepare a large number of analogues

for pharmacological screening studies (Scheme2).

(i) Why do we not use this method today?

(ii) Derive a mechanism for this reaction.

OKCN, (NH4)2CO3

EtOH, ∆ HNNH

O

O Scheme 2 Bergs synthesis of phenytoin

Experiment 2 Preparation of Nitrazepam Introduction

The discovery in 1957 by L. O. Randell of the tranquillising and sedative properties of

chlorodiazepoxide (Librium) (1), prepared two years earlier by L. H. Sternbach at

Hoffman La Roche laboratories, was the starting point for much pharmacological and

chemical research leading to the important class of anxiolytic drugs known as

benzodiazepines. Many substances of this group are used in anxiolytic, hypnotic and

anticonvulsant therapy. The original Sternbach procedure is difficult to implement in

teaching laboratories and we will use a modified procedure to prepare nitrazepam (2) a

nitrated benzodiazepine derivative.

N

N

ClO

NHCH3

N

HN

O2N

O

(1) (2) NOTE: This product is pharmacologically active and should be handled with extreme

care.

Objectives Synthesis and purification of Nitrazepam and analysis of the purity of intermediates and

product by TLC, IR and melting point. Application of a three step synthetic process to

form a pharmaceutical product.

Procedure

Step 1. Preparation of 2-bromoacetamido-5-nitrobenzophenone

NH2

O2NO

NH

O2NO

O

Br

Toluene, ∆

Br Br

O

Materials Bromoacetyl bromide 3.23 g, 16 mmol Irritant

2-amino-5-nitrobenzophenone 3 g, 12.4 mmol Irritant

Toluene 20 ml Irritant

Bromoacetyl bromide (3.23 g, 1.4 ml, 16 mmol) is added dropwise to a stirred solution of

2-amino-5-nitrobenzophenone (3 g, 12.4 mmol) in toluene (20 ml) at room temperature

and then heated to reflux on a steam bath for 30 minutes. (NOTE: CARE hydrogen bromide gas is evolved. Carry out all procedures in a fume hood). On cooling, the

product crystallises out from the reaction mixture and is isolated by filtration to yield a

yellow solid. Record the yield of your product and its IR spectrum and melting point.

Step 2. Preparation of 2-Azidoacetamido-5-nitrobenzophenone

NH

O2NO

O

Br NaN3

Ethanol, ∆

NH

O2NO

O

N3

Materials 2-bromoacetamido-5-nitrobenzophenone 2.0g, 5.5 mmol Irritant

Sodium azide 0.45 g, 6.9 mmol Toxic / Explosive

Ethanol 30 ml Irritant

Acetone 20 ml Irritant

NOTE: Sodium azide is toxic and is potentially explosive. Pre-weighed samples will be provided for you, and this compound should not be handled directly by undergraduate student.

2-Bromoacetamido-5-nitrobenzophenone (2.0 g, 5.5 mmol) and sodium azide (0.45g, 6.9

mmol) in ethanol (30 ml) are refluxed for 30 minutes and then acetone (20 ml) is added

carefully to redissolve the crude azide. The mixture is then filtered while hot to remove

any residual sodium azide before concentrating to approximately 40 ml to precipitate the

azide product that is collected by filtration to yield the product as a white solid used

directly in the next reaction.

Step 3. Preparation of Nitrazepam

NH

O2NO

O

N3 Ph3P

Toluene, ∆

( - N2)

N

HN

O2N

O

Materials 2-azidoacetamido-5-nitrobenzophenone 1.5 g, 4.6 mmol Irritant

Triphenylphosphine 1.82 g, 5 mmol Irritant

Toluene 20 ml Irritant

2-Azidoacetamido-5-nitrobenzophenone (1.5 g, 4.6 mmol) and triphenylphosphine (1.82

g, 5 mmol) in toluene (20 ml) are stirred at room temperature until no more nitrogen is

evolved and all solids completely dissolve to give a yellow solution. The mixture is then

refluxed for one hour with occasional stirring. The toluene is then removed on a rotary

evaporator, the residue can be crystallised by the addition of ethanol (10 ml) to give the

product as a yellow solid that is isolated by filtration. Recrystallisation from

approximately 30-40 ml of ethanol gives the product as a light yellow solid.

Questions

(i) Describe the stereochemistry of the benzodiazepines.

SOME HAZARDS ASSOCIATED WITH MATERIALS USED ON THIS PRACTICAL COURSE

Acetone b.p 56°C

Highly Flammable

2-Amino-5-nitrobenzophenone Irritating to eyes, skin and respiratory

system

Benzil Irritating to eyes, skin and respiratory

system

Bromoacetyl Bromide Causes burns. Irritating to eyes and

respiratory system.

Ethanol b.p. 78°C

Highly flammable. Irritating to eyes,

respiratory system and skin.

Ethyl Acetate b.p. 77°C

Highly flammable

Hexane b.p. 68°C

Highly flammable. Possible serious

damage to health by prolonged exposure

through inhalation.

Hydrochloric Acid Causes burns. Irritating to eyes, skin and

respiratory system.

If contact with eyes flush with copious

amounts of water for 15 minutes while

keeping eyelids separated. Wash skin with

soap. If inhaled remove to fresh air.




soap.




soap.




















soap.

Methanol b.p. 65°C

Highly flammable. Toxic by inhalation and

if swallowed.

Potassium Hydoxide Causes severe burns

Sodium Azide Very toxic if swallowed. Contact with

acids liberates toxic gas.

Toluene Highly flammable. Harmful by inhalation.

Triphenyl Phosphine Harmful if swallowed.

Urea Toxic by inhalation, by contact with skin

and if swallowed. Irritating to eyes, skin

and respiratory system.








soap.




soap.








soap.




soap.

pf3002 lab manual

Documents

keeping eyelids separated

irritant irritant irritant

fume cupboard

data sheet

organic chemistry

yellow solid

sodium azide

data sheets