PHG 461. King Saud University Pharmacy Collage Pharmacognosy Depaartment LAB#3 Spectrophotometric determination Of Aminopenicillins by using sorbitol.

PHG 461

King Saud UniversityPharmacy Collage Pharmacognosy Depaartment

LAB#3

Spectrophotometric determination Of Aminopenicillins by using

sorbitol method.

Aminopenicillins-:

The 3 clinically useful aminopenicillins are:

• Ampicillin

• amoxicillin

• cyclacillin

S

N

O

R-CONH

CH3

CH3

COOH

R=

CHCH3

NH2

R=

HCCH3

NH2

HO

R= NH2

Reaction of Penicillins with amines or alcohol:

AminesAlcohol- Polyhydric alcohol

Glucose-sorbitol

1) Nucleophilic attack of B-lactam Penicilloyl derv.(A&B)

2) Piperazine 2,5-dione

Spectrophotometric determination of amino penicillins

S

N

O

R-CONH

CH3

CH3

COOH

HN

S

O

R-CONH

CH3

CH3

COOHNH-R'

(A)

HN

S

O

R-CONH

CH3

CH3

COOHO-R'

R’NH2

Amine

R’OH

Alcohol

(A) (B)

Imidazole

Principle of assay:

Aminopenicillin +polyhydric alcohol

( sorbitol contain zn ion as catalyst)

60c0/10 minWB

Piperazine 2,5-dione derivative

By reaction with 1M

NaOH

Adrevative of ɻ MAX

@322nm which can be assayed

spectrophotometrically

Requirement for reaction occure-:

Two requirement

1-intact amino side chain

2-intact B-lactam ring are required for piperazine dione formation

So, the method is highly specific for determinig the purity of aminopenicillins as their decomposition products do not interfere with its accuracy also ampicillin polymers & dimers if polymerization or dimerization occur due to bad storage it will not interfere with the accuracy of assay

WHY.?

Amoxicillin Dimer

The presence of ampicillin dimers or polymers does not interfere with the accuracy of this assay this is due to the fact that an intact amino side-chain & intact B-lactam ring are required for the dione formation which is not available in polymers or dimers.

N.B-:

1)Attachment to B-lactam ring is facilitated by metal ions (ZN++ OR CU++ as catalyst )

2 )This method can not be use for determination of benzyl penicillin & flucloxacillin Because it does NOT have free amino in side-chain.

3 )Although the B-lactam ring opening can be achieved with any polyhydric compound (e.g.,glucose, or fructose ) sorbitol is preferred as it gives lower blank reading, this is because it has no function (carbonyl ) group.

Benzylpenicillin flucloxacillin

4)Sorbitol reagent consist of ;(sorbitol+zn ion+ carbonat)

a- sorbitol is polyhydric alcohol opens B- lactam ring to yield ester (penicilloic acid)

b- Zn ion act as catalyst for such reaction

c- Carbonate adjust PH at 9.5 it keep the medium alkaline so that the amino group kept in unionized free form

it is found that formation rate of penicilloyl ester increase with increasing pH & it max.@ pH 10.5

Once,this ester is formed it yield piperazine 2,5 dione which decompose quickly @ high pH(about pH=9.6)

So, @pH=9.5(alkaline)

1-free un ionized amino gp

2-ester formed @reasonable rate

3-piperazine dione formed is stable for hour

Procedure-:

1)2 volumetric flask 10 ml (A&B) put in each one 1ml of sample by pippet

2)Add 7 ml sorbitol reagent only to A

3)Add 7 ml distelled water to B

4) Stopper the flask & heating them in W.B 60c0 for 10 min

5)Complet the volume with sorbitol to 10 ml in flask A

Procedure :- cont.

6 )Complet the volume with distelled water to 10 ml in flask B

7 )From these solutions transfer 1 ml into test tube by pippet

8 )Add 5 ml 1M NaOH by mesure for both test tube A&B

9 )Mix well &mesure the absorbance @322nm by using spectrophotometer

10 )Reading should be taken within 3-5 min

Blank:

Mixture of 1ml H2O and 5 ml 1M NaOH

Calculation-:

A`- B`

Conc. Of sample=

A - B x standard conc.

A`- B`

A - B Sample conc .

Standard conc .

Mg/ml

A`- B`

A - B

Standard absorbance

Sample absorbance

Standard conc.=1mg/ml

A`=0.46

B`=0.06

Data given-:


LAB#4

Use of Imidazole in Spectrophotometric assay of Penicillins

LAB#4


Reaction of Penicillins with amines: Amine

s

1) Nucleophilic attack of B-lactam Penicilloyl derv.(A)

2) Mercaptane

S

N

O

R-CONH

CH3

CH3

COOH

HN

S

O

R-CONH

CH3

CH3

COOHNH-R'

(A)

R’NH2

Amine

(A)

Imidazole


• Imidazole can be used in spectrophotometric assay of all Penicillins e.g.Benzylpenicillin, Amoxycillin and Flucloxacillin.

• Aminopenicillins such as, ampicillin and amoxicillin have free amino group which is responsible for the instability of the mercaptide derivative formed.

• Acetic anhydride-dioxan reagent is used in the assay of such compounds to block the free amino group by acetylation so that the mercaptane formed is stable and piperazine 2,5-dione not formed.

Comment:


• The mercaptane is measured spectrophotometrically at 325nm.

• Benzylpenicillin has no free amino group so the formed mercaptane is stable.

• Flucloxacillin has no free amino group so the formed mercaptane is stable, but it is mesured at =346nm bec. It has more chromophore groups that responsible for absorption in UV i.e. more conjugated double bond.

Comment:


• This method of assay requires only the presence of intact B-lactam ring.

• It is sensitive method with strong absorption at 325nm can be used to detect a conc. as little as 0.5Mg/ml.

• Can be used specifically for assaying amoxicillin in presence of its acid or alkali degradation products.

• Dimers & polymers can interfere with such determination since they have intact B-lactam ring

• Mercury act as catalyst.

Comment:

Amoxicillin Dimer


Procedure:

100ml

10ml of sample by pipette+10 ml boric buffer + 1ml acetic anhydride-dioxan reagent

Stand

5’

Complete the volume e’distilled water (1)

Pipette 2ml of (1)

25ml 10ml Imidazole-

mercury reagent

Mix heat on W.B. at 60C for 25min.

Cool rapidly to 20C

(A)

25ml + 10ml

H2O

Mix (B)

Measure ab. rapidly


Procedure:

- 2ml H2O+10ml Imidazole-mercury reagent for A

- water for B

Measure abs. of A&B at 325nm

Blank:


Calculation:

Absorbance of Standard (A) = 0.456

Absorbance of Standard (B) = 0.016

Conc. of standard= 5mg/ml

Conc.5mg/ml Abs.of st. (A-B)

Conc. of unknown ?

Abs. of unk. (A-B)


LAB#5

The maltol method for the assay of streptomycin

*Streptomycin is a bactericidal antibiotic belong aminoglycoside class

*It kills sensitive microbes by inhibiting protein synthesis

*An adverse effect of this medicine is ototoxicity, which can lead in temporary hearing loss.

streptomycin

ß

ą

streptidine

L-streptose

N-methylglucosamine

streptomycin sulphate

streptobiosamine}

streptomycin

Principle:

Hydrolysis by alkali

aglycone (genin) striptidine+

glycone (disaccharide sugar) streptobiosamine

streptobiosamine

Principle:

Hydrolysis by alkali

N-methylglucosamine +L-streptose

Cont.

maltol ferric ion in

acidic media

Purple color

decomposed

purpel color that can be measured quantitatively @

540nm (visible region)?????N.B:

(** UV region )200-380nm

(** visible region)380-800nm

ß

ą

streptomycin sulphate

HydrolysisBy alkali lead to break

Glycosidic linkage

streptobiosamine

H

streptobiosamine

o

o

OH

CH32-cyclization of L-streptose

maltol

Fe+++

Purple color

H 1-Hydrolysis by alkali &break disaccharide linkage

Procedure:* aquous solution of sample is prepared to

contain 1mg of streptomycin base per ml of solution

1-take 10ml of the provided solution into 25ml

volumetric flask (pippet)

2-add 2ml of 1N sodium hydroxide (measure)& must

be stoppered lossely

3-immerse the flask in boiling water bath(100c0) for 3-4 min.

Procedure:

4-cool for 3min, then add 4ml of ferric ammonium sulfate (2%ferric ammonium sulfate in 1N H2SO4) (mesure)

5-dilute to volume with water, & allow to stand for

10min.

6-measure absorbance @540nm versus blank

Cont.

Procedure cont:.

1-take 10ml of the water into 25ml volumetric flask

2-add 2ml of 1N sodium hydroxide (measure) )&

must be Stoppard lossely

3-immerse the flask in boiling water bath for 3-4 min.

4-cool for 3min, then add 4ml of ferric ammonium sulfate (mesure)

5-dilute to volume with water, & allow to stand for

10min.

Blank

Comment:1-the amount of streptomycin contained in sample

can be found by doing comparison with standard solution of pure streptomycin which subjected for same procedure

2-alkali (NaOH) act on the glycosidic linkage then on the disaccharide (i.e alkaly cleave genin & sugar part)

3-boiling period 3-4min. After addition alkaly to ensure complete hydrolysis

4-stoppering & cooling are essential since maltol is steam volatile

5- cooling is essential to avoid turbidity due to Fe(OH)3 formation, turbidity is make difficulty to mesure absorbance because absorbance here depend on color

6- acid (ferric ammonium sulfate) over come alkalinity so, ferric hydroximate is not formed

Cooling

Due to maltol is steam volatil

To avoid ferric hydroximate formation

ferric hydroximate is inhibit it formation by

cooling addition of acid( ferric ammonium sulfat)

7-this method is very sensitive & can be use for analysis of streptomycin in biological fluid

8- dihydrostreptomycin does not yield maltol under this condition thus, if present it will not interfere with analysis of streptomycin

(dihydrostreptomycin has CH2OH instead of CHO so,it is unable to give maltol it will not interfere with such assay)

9-color is stable for 24 hr

10-maltol is steam volatile so, use Stoppard volumetric flask &cool

Calculation: %conc. Of streptomycin=

absorbance of sample x conc. Of sample

absorbance of standard

X 100

Absorbance for standard =0.611

Conc. Of sample: 1 mg 1ml

x 10ml

x=10mg=0.01g

Using Stoppard volumetric flask

Lab#6

Practical exam1

PHG 461. King Saud University Pharmacy Collage Pharmacognosy Depaartment LAB#3 Spectrophotometric determination Of Aminopenicillins by using sorbitol.

Documents

b imidazole slide

catalyst slide

naoh slide

hour slide

flask b

b lactam ring

amoxicillin dimer slide

blactam ring opening