Crystalline form III of agomelatine, a process for its preparation and pharmaceutical compositions containing it

The present invention relates to a new crystalline form III of agomelatine, or N-[2-(7-methoxy-1-naphthyl)ethyl]acetamide, of formula (I):

a process for its preparation and pharmaceutical compositions containing it.

Agomelatine, or N-[2-(7-methoxy-1-naphthyl)ethyl]acetamide, has valuable pharmacological properties.

Indeed it has the double feature of being, on the one hand, an agonist of melatoninergic system receptors and, on the other hand, an antagonist of the 5-HT 2C receptor. Those properties confer activity in the central nervous system and, more especially, in the treatment of severe depression, seasonal affective disorders, sleep disorders, cardiovascular pathologies, pathologies of the digestive system, insomnia and fatigue resulting from jetlag, appetite disorders and obesity.

Agomelatine, its preparation and its therapeutic use have been described in European Patent Specification EP 0 447 285.

In view of the pharmaceutical value of this compound, it has been important to be able to obtain it with excellent purity, with well defined crystalline form, perfectly reproducible, which as a result exhibits valuable characteristics in terms of formulation and sufficiently stable to allow its storage for long periods without particular requirements for temperature, light, humidity or oxygen level.

Patent Specification EP 0 447 285 describes the preparation of agomelatine in eight steps, starting from 7-methoxy-1-tetralone. However, that document does not specify the conditions for obtaining agomelatine in a form that exhibits those characteristics in a reproducible manner.

The Applicant has now developed a new synthesis process that allows agomelatine to be obtained in a well defined, perfectly reproducible crystalline form that especially exhibits valuable characteristics for formulation.

More specifically, the present invention relates to the crystalline form III of the compound of formula (I), characterised by the following powder X-ray diffraction diagram, measured using a Siemens D5005 diffractometer (copper anticathode) and expressed in terms of inter-planar distance d, Bragg's angle 2 theta, intensity and relative intensity (expressed as a percentage of the most intense ray):

The invention relates also to a process for the preparation of the crystalline form III of the compound of formula (I), which process is characterised in that agomelatine is heated at 110° C. until the melting be completed, and is then slowly cooled until crystallisation.

An advantage of obtaining that crystalline form is that it allows the preparation of pharmaceutical formulations having a consistent and reproducible composition, which is especially advantageous when the formulations are to be used for oral administration.

A pharmacological study of the form III so obtained has demonstrated that it has substantial activity in respect of the central nervous system and in respect of microcirculation, enabling it to be established that the crystalline form III of agomelatine is useful in the treatment of stress, sleep disorders, anxiety, severe depression, seasonal affective disorders, cardiovascular pathologies, pathologies of the digestive system, insomnia and fatigue due to jetlag, schizophrenia, panic attacks, melancholia, appetite disorders, obesity, insomnia, pain, psychotic disorders, epilepsy, diabetes, Parkinson's disease, senile dementia, various disorders associated with normal or pathological ageing, migraine, memory loss, Alzheimer's disease, and in cerebral circulation disorders. In another field of activity, it appears that the crystalline III form of agomelatine can be used in the treatment of sexual dysfunction, that it has ovulation-inhibiting and immunomodulating properties and that it lends itself to use in the treatment of cancers. The crystalline form III of agomelatine will preferably be used in the treatment of severe depression, seasonal affective disorders, sleep disorders, cardiovascular pathologies, insomnia and fatigue due to jetlag, appetite disorders and obesity.

The invention relates also to pharmaceutical compositions comprising as active ingredient the crystalline form III of agomelatine together with one or more appropriate inert, non-toxic excipients. Among the pharmaceutical compositions according to the invention there may be mentioned, more especially, those which are suitable for oral, parenteral (intravenous or subcutaneous) or nasal administration, tablets or dragées, granules, sublingual tablets, gelatin capsules, lozenges, suppositories, creams, ointments, dermal gels, injectable preparations, drinkable suspensions and disintegrable pastes.

The useful dosage can be adapted according to the nature and the severity of the disorder, the administration route and the age and weight of the patient. The dosage varies from 0.1 mg to 1 g per day in one or more administrations.

The Examples below illustrate the invention but do not limit it in any way.