Secobarbital

IUPAC nomenclature

5-(pentan-2-yl)-5-(prop-2-en-1-yl)-1,3-diazinane-2,4,6-trione

Classification 

Secobarbital is a barbiturate sedative-hypnotic.

Physiochemical Properties

Mechanism of Action

i. Drug binds with different binding sites associated with chloride ionopore at the GABA_A

ii. This results in increase in the duration of time for the opening of the chloride ionopore.

iii. As a result, the post synaptic inhibitory effect of GABA in the thalamus is prolonged.

Structure Activity Relationship

• Tri-keto form is most stable in aqueous solution.
• 4,6-dialcoholic tautomeric forms are least stable in aqueous solution.
• 5,5-disubstituted barbituric acid is the prime requirement for the barbiturates to be sedative hypnotics.
• Esterification of either of the 1,3-diazine nitrogens decreases hypnotic activity.
• Substitution of either of the 1,3-diazine nitrogens with aliphatic carbons retains the anticonvulsive properties.
• Esterification of the 5^th-position substituents yields agents with analgesic activity but with weak hypnotic properties.
• Introduction of the polar functional group at the 5^th– position yields compounds which are fully devoid of sedative-hypnotic or anticonvulsive activity.
• As the number of carbons at R₂ carbon increases, the lipophillicity of the drug increases.
• Modification of the 2^nd-position oxygen of the barbiturate backbone with sulfur atom yields thiobarbiturate derivatives with increased lipophillicity, shorter duration of action, faster time of onset compared to oxy-derivative. [1]

Method of synthesis

Secobarbital can be synthesized by reaction of α-allyl-α-(1-methylbutyl)-malonic ester with urea.[2]

Therapeutic Uses

Secobarbital is used for:

• Treatment of seizures
• For producing sedation during the time of anxiety.

Side Effects

Side effects of Secobarbital are:

• Insomnia
• Dizziness
• Drowsiness
• Loss of coordination
• Nausea
• Vomiting
• Constipation
• Restlessness
• Headache
• Loss of appetite
• Pale skin
• Shallow breathing

MCQ

 Q.1 Choose the correct statements related to the physicochemical properties of drug secobarbital-

I. Molecular weight is 238.28 gm/mol

II. White amorphous crystalline powder

III. It is very soluble in water

IV. Melting point is 325K 

a) I, II

b) I, II, III

c) III, IV

d) I, III, IV

Q.2 Match the following of the drugs with their correct Trade names.

 a) i-B, ii-C, iii-D, iv-A

b) i-B, ii-C, iii-A, iv-D

c) i-C, ii-A, iii-D, iv-B

d) i-A, ii-D, iii-B, iv-C

Q.3 Effect produced due to binding of secobarbital with GABA_A receptor??

a) Increase in GABA affinity for GABA receptor

b) Decrease in GABA affinity for GABA receptor

c) Blocking of GABA receptor for GABA

d) None of the above

Q.4 Correct sequence for True/false for the classification of the drug can be?

• Secobarbital: Neuraminidase inhibitor analogue
• Phenobarbital: Non-nucleoside reverse transcriptase inhibitor
• Ribavirin: Conventional nucleoside analogue
• Tipranavir: HIV protease inhibitor

a) FFTT

b) TTTF

c) FTTT

d) TFTT

Q.5 Esterification of either of the 1,3-diazine nitrogens of secobarbital results in?

a) Decrease in hypnotic activity

b) Increase in hypnotic activity

c) Bioavailability increases

d) Bioavailability decreases

Q.6 Type/s of ring present in the structure of secobarbital?

I. Pyrimidine

II. Indole

III. Benzene

a) II, III

b) I, II

c) I

d) I, II, III 

Q.7 Side effect of drug Secobarbital?

a) Insomnia

b) Dizziness

c) Loss of coordination

d) All of the above

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ANSWERS

1-c

2-c

3-a

4-a

5-a

6-c

7-d

REFERENCES