Quinazoline Alkaloids

2.2.1 Quinazoline Alkaloids

Vasicine is a quinazoline alkaloid which will be described below.

A. Vasicine

Synonym Peganine

Biological Sources It is obtained from the leaves of Adhatoda vasica (L.) Nees (Acanthaceae) (Malabar Nut, Adotodai, Paveltia); and the seeds of Peganum harmala L. (Rutaceae) (Harmel, Syrian Rue, African Rue).

Chemical Structure

1, 2, 3, 9-Tetrahydropyrrolo [2, 1-b] quinazoline-3-ol; (C₁₁H₁₂N₂O).

Isolation It is isolated from the leaves of Adhatoda vasica* and also from the seeds of Peganum harmala** by adopting the standard methods of isolation described earlier in this chapter.

Characteristic Features

dl-Form: 1. It is obtained as needles from ethanol having mp 210°C.

2. It sublimes on being subjected to high vacuum.

3. It is soluble in acetone, alcohol, chloroform; and slightly soluble in water, ether and

benzene.

l-Form: 1. It is obtained as needles from ethanol with mp 212°C.

2. Its specific rotation [α ]_D¹⁴ -254⁰ (C = 2.4 in CHCl₃); [α ]_D¹⁴–14  62° (C = 2.4 in ethanol).

Note: In dilute HCl it is obtained as its dextrorotatory form.

Identification Tests

1. Hydrochloride dihydrate derivative is obtained as needles having mp 208°C (dry).

2. Hydroiodide dihydrate derivative is formed as needles with mp 195°C (dry).

3. Methiodide derivative is obtained as needles from methanol having mp 187°C.

4. Acetyl vasicine derivative (C₁₁H₁₁N₂O COCH₃) is formed as crystals having mp 123°C and bp0.01 230-240°C.

Uses

1. It is mostly used as an expectorant and bronchodilator.

2. It also shows oxytocic properties very similar to those exhibited by oxytocin and methyl ergometrine.

3. Vasicine also shows abortifacient action which is due to the release of prostaglandins.

Biosynthesis of Vasicine Various studies in Peganum harmala have evidently revealed vasicine (peganine) to be derived from the anthranilic acid, while the remaining portion of the structure comprising of a pyrrolidine ring provided by ornithine. The probable mechanism of vasicine skeleton may be explained by virtue of the nucleophilic attack from the N-atom present in anthranilate upon the pyrrolidinium cation, ultimately followed by amide formation. However, interestingly this pathway is not being adopted in Justicia adhatoda. Thus, a comparatively less predictable sequence from Nacetylanthranilic acid and aspartic acid is observed as shown below:

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* Sen, Ghosh, J. Indian Chem. Soe., 1, 315 (1924);

** Späth, Nikawitz, Ber. 67, 45, (1934);

B. Vasicinone

Biological Source The plant source remain the same as described under vasicine.

Chemical Structure

1, 2, 3, 9-Tetrahydropyrrolo [2, 1-b] quinazoline-6-one-3 ol (C₁₁H₁₀N₂O₂).

Uses It is used mainly as an expectorant which action is solely due to stimulation of the bronchial glands.
Source:Pharmacognosy And Pharmacobiotechnology By Ashutosh Kar