Description
Epinastine hydrochloride, an orally active antihistaminic agent, was marketed in
Japan for the treatment of bronchial asthma, allergic rhinitis, urticaria, eczema,
dermatitis, and psoriasis vulgaris.Epinastine is one of the most effective
peripherally acting histamine H
1-receptor antagonists without sedative effects.In
addition, it exhibits potent anti-PAF and anti-LT activity which may also contribute
significantly to its antiallergic activity. Chronic epinastine has been reported to
effectively inhibit airway hyper-responsiveness in rats. Potent inhibitory effects of
epinastine on bronchoconstriction induced by histamine and bradykinin, but not by
other chemical mediators, has also been reported. Studies have indicated that there
are no significant differences in pharmacological properties among D-, L-, and
racemic epinastine.
Originator
Boehringer
lngelheim (Germany)
Uses
Epinastine is antihistamine and mast cell stabilize that is used in eye drops for the treatment of allergic conjunctivitis.
Definition
ChEBI: A benzazepine that is 6,11-dihydro-5H-dibenzo[b,e]azepine in which the azepine ring is fused to the e side of 4,5-dihydro-1H-imidazol-2-amine.
Clinical Use
Epinastine is a potent, long-acting H1 antihistamine and an inhibitor of the release of
histamine and other transmitters from mast cells. It has some affinity for H2 receptors as well.
It is used as an eye drop for allergic conjunctivitis. It does not penetrate into the CNS and is
classified as a nonsedating antihistamine.
Synthesis
Several patents on the synthesis of
epinastin (VIII) have appeared in Europe and Japan.
The synthesis described below is taken partly from the US
patent and a Japanese patent. All the syntheses
utilized 6-aminomethyl-6,11-dihydro-5H-dibenzo[b.e]azepine
(80) as the key intermediate which was converted to the final
guanidine epinastine by reacting with cyanogen bromide.
The solution of 80 in ethanol was treated with a solution of
cyanogen bromide in THF at room temperature and stirred
overnight. The hydrobromide salt was collected in 79%
yield after adding ether to the reaction mixture. The salt was
free based with a solution of sodium hydroxide and then
treated with an ethereal solution of HCl to obtain the
epinastine hydrochloride salt VIII. For the preparation of the
key intermediate, chloroimine 78, presumably obtained from
ketone 77 via Beckmann rearrangement, was reacted
with sodium cyanide in DMSO to give the nitrile 79 in 70%
yield. Reduction of the imino nitrile was carried out in THF
in the presence of an acid with LAH to give the key
intermediate 80 in 67% yield.
An alternate approach to preparation of 80 is shown in
Scheme 8 as well. Reaction of the commercially available
chloride 81 with phthalimide in the presence of a
base gave the phthalimide 82. Reduction of the imine with
sodium borohydride gave 83, which was then reacted with
hydrazine hydrate to free up the amine in 90% yield. The
amine intermediate was isolated as the fumarate salt.
