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`Petition for Inter Partes Review of US 8,242,158
`Amneal Pharmaceuticals LLC – Exhibit 1005 – Page 1
`
`

`

`4,910,214
`
`1
`
`OPTICAL ISOMER OF AN IMIDAZOLE
`DERIVATIVE MEDETOMIDINE AS AN
`ALPHA-2-RECEPTOR AGONIST
`
`This invention relates to optical isomers of imidazole
`derivatives and to their preparation.
`Medetomidine which has the formula:
`
`CH;
`|cH
`
`|
`
`CH;
`
`‘CH;
`
`«
`
`N
`
`*
`H
`
`is knownas a selective and potent a2-receptor agonist.
`It has been described, e.g. in European Patent Publica-
`tion No. 72615, as an antihypertensive agent and in the
`European Patent Publication No. 187471 as a veterinary
`sedative-analgesic agent.
`The present invention provides, as new compounds,
`the optically active d- and l-enantiomers of medetomi-
`dine, and their non-toxic pharmaceutically acceptable
`acid addition salts. These compounds may be repre-
`sented by the formulae:
`
`5
`
`10
`
`15
`
`20
`
`30
`
`35
`
`45
`
`2
`nates, formates, tartrates, maleates, citrates, benzoates,
`salicylates, ascorbates and the like.
`The d- and |-enantiomers of medetomidine are selec-
`tive and potent a2-receptor agonists.
`Adrenergic receptors are physiologically important
`binding sites which are specific to noradrenaline and
`adrenaline and located on the surface of the cell mem-
`brane. The adrenoceptors of the sympathetic nervous
`system have beenclassified into two different subtypes,
`alpha-(a) and beta-(8) receptors, which can be further
`divided into two subgroups, viz a; and azand 8) and £2.
`Of these receptor types, 8), 62 and a, are mainly lo-
`cated post-synaptically on the surface of, e.g., smooth
`muscle and thus mediate, e.g., smooth muscle contrac-
`tion or relaxation; whereas a2 receptors are mainly
`located presynaptically on the terminals of noradrener-
`gic nerves. If a2-receptors are stimulated by noradrena-
`line under physiological conditions noradrenaline re-
`lease is blocked, i.e. there is a negative feed-back phe-
`nomenon. This negative feed-back phenomenon may
`also be induced by certain synthetic a2-agonists like
`medetomidine and someofits near derivatives.
`In animal experiments, the d- and I- enantiomers of
`the present invention and especially the d-enantiomer,
`have proved to possess highly enhanced az-selectivity
`and potency compared to the racemic mixture (i.e.
`medetomidine). The d-enantiomercan be expected to be
`ofvalue,e.g., as a sedative-analgesic, anxiolytic or anti-
`hypertensive agent. Furthermore, it can be used as a
`pharmacological tool in the study of the physiology and
`pharmacology of a2-adrenoceptors.
`The pharmacological activity of the compounds of
`the invention was determined as follows:
`
`1. ALPHA-2 AGONISM IN VITRO
`
`@2-agonism was determined by means of isolated,
`electrically stimulated mouse was deferens preparation
`(Marshall et al., Br. J. Pharmac. 62, 147-151, 1978). In
`this model, an a2-agonist is able to block electrically
`induced muscular contractions by activating the presy-
`naptic a2-adrenoceptors and thus diminishing the secre-
`tion on the motortransmitter. Known a-agonists like
`detomidine, medetomidine and clonidine were used as
`reference substances. Results are shown in Table 1,
`where the a2-agonist effect is presented as the pD2-
`value (negative logarith of the molar concentration of
`the compoundproducing 50 percent of maximalinhibi-
`tion.)
`
`TABLE |
`@2-agonism in vitro (mouse
`vas deferens). pD2
`9.3
`6.0 (partial agonist)
`9.0
`8.5
`8.5
`
`Compound
`d-enantiomer
`l-enantiomer
`medetomidine
`detomidine
`clonidine
`
`Ty
`
`CH;
`
`=e
`
`H
`
`CH3
`
`CH3
`
`N
`
`N
`i
`
`H
`
`ach;
`
`¢
`
`NOmeCH;
`
`CH3
`
`N
`I
`
`According to a feature of the invention, racemic
`medetomidine is separated into the enantiomers II and
`III by conversion of the racemate into a mixture of
`diastereoisomers and separating the latter by fractional
`crystallization. Since medetomidineis a base, it may be
`converted into a diastereoisomersalt mixture by reac-
`tion with an optically active acid such as (+)-tartaric
`acid. Other useful optically active acids are, e.g., (—)-
`malic acid, (—)-mandelic acid and (+)-camphor-10-sul-
`fonic acid. (+)-Tartaric acid is especially useful for the
`resolution. The separation of the diastereisomers is per-
`formed by repeated crystallizing from an alcohol such
`as methanol or ethanol or a mixture of them.
`Once the diastereoisomers have been separated the
`acid addition salts can be converted back to the free
`bases by making their aqueous solutions alkaline with
`sodium hydroxide and by extracting the liberated base
`in an appropriate organic solvent such as methylene
`chloride.
`The d- and |-enantiomers of medetomidine react with
`organic and inorganic acids to form the corresponding
`acid addition salts, which have the same therapeutic
`activities as the bases. They can thus form many phar-
`maceutically usable acid addition salts, as, for instance,
`chlorides, bromides, sulfates, nitrates, phosphates, sulfo-
`
`60
`
`65
`
`the a2-agonist activity of
`These results show that
`medetomidine is limited to the d-enantiomer. The d-
`enantiomer showsan enhanced a2-agonist activity com-
`pared to the outer agents studied.
`2. a2/a,;-SELECTIVITY IN VITRO
`
`Theselectivity of the d-enantiomer as an a2-agonist
`was studied in receptor binding experiments using rat
`brain membranes. The ability of the d-isomer and the
`reference compounds to compete with H-clonidine
`
`Petition for Inter Partes Review of US 8,242,158
`Amneal Pharmaceuticals LLC — Exhibit 1005 — Page 2
`
`

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`Petition for Inter Partes Review of US 8,242,158
`Amneal Pharmaceuticals LLC – Exhibit 1005 – Page 3
`
`

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`Petition for Inter Partes Review of US 8,242,158
`Amneal Pharmaceuticals LLC – Exhibit 1005 – Page 4
`
`