BACKGROUND ART Morphine and its known derivatives are opiates which have pain relief properties, and are therefore useful in the treatment of chronic and acute pain encountered in various indications in humans and other warm blooded animals. Certain known derivatives may also be used as antidotes in situations of abuse or overdose.

Some morphine derivatives are described in PCT applications numbers GB 92/01449 and GB 93/02605, the disclosures of which are incorporated herein by way of reference. These references also disclose a particularly advantageous, new process for the preparation of morphine derivatives which avoids the use of heavy metal salts. A particularly preferred morphine derivative therein is morphine-6-glucuronide.

DISCLOSURE OF THE INVENTION It has now been found that a certain morphine-6-glucuronide analogue has particularly useful enhanced agonist opioid activity.

According to the present invention, there is provided a morphine-6- glucuronide analogue having the formula 1-(7, 8-dihydromorphine-6-yl)-ß-D- glucopyranosiduronic acid (I), and acid addition and metal salts thereof.

In the morphine structure (ici), a number of sites are capable of substitution and modification. For example the ester substituent at position 6 may be pyranose, furanose and uronic acid derivatives thereof ; the substituent at the cyclic nitrogen may be for example, hydrogen, lower alkyl (Cl to Cg), substituted lower alkyl in which the substituents may be aryl, such as for example phenyl, carboxylic acid and esters thereof, and cycloalkyl, for example, cyclopropyl, and N-oxide; the phenolic group may also be alkylated or esterified.

According to the present invention, it has been found that the morphine derivative, wherein the nitrogen substituent is methyl, the ether substituent at position 6 is derived from glucuronic acid, and the ethylenic bond bridging position 7-and 8-is hydrogenated, has enhanced opioid agonist activity compared to morphine in that it has a higher affinity for the opioid

analgesia receptor (, ut), and increased anti-nociceptive activity in an animal pain model, as detailed in table 1. Enhanced activity is also attainable when the ethylenic bond bridging position 7-and 8-is modified by other adducts, whereby instead of dihydro, the 7-8-position may be dihydro-, dihydroxy-, hydroxyhalo-, epoxy-, dihalo-, hydrohalo-, hydrohydroxy-, or CXY (X, Y is halogen or hydrogen) adducts.

The compound of the present invention may be in form of an acid addition salt, such as for example sulphate, hydrochloride, acetate, maleat, tartrate, citrate; and it may be in the form of an alkali metal or alkaline earth salt, such as for example sodium, potassium, lithium, calcium. The compound may also be in form of a hydrate or solvate.

The present invention includes the compound of the present invention in any crystalline form.

The compound of the present invention may conveniently be prepared by the following route starting from morphine sulphate.

1. Protection of the 3-phenolic group by acylation.

2. Protection of the hydroxyl and carboxylic acid groups of D-glucuronolactone.

3. Condensation of the products of 1 and 2 above.

4. Removal of the protecting groups of the condensation product 3 to yield morphine-6-glucuronide.

5. At any stage as appropriate hydrogenation of morphine-6-glucuronide

to yield the product of the present invention.

The compound of the present invention may be administered by any convenient parenteral route. The dose may be varied as required, but will generally, for example, be in the range 0.01 mg/kg to 0.30 mg/kg for patients starting on a strong analgesic, and may be administered continuously, for example, intravenously or subcutaneously.

DESCRIPTION OF THE PREFERRED EMBODIMENT The invention is illustrated with reference to the following examples.

Example 1 <BR> <BR> 1- (7, 8-Dihydromorphin-6-yl)-, (D-glucopyranosiduronic Acid. Morphine-6- glucuronide (2.00g, 4.02mol), prepared as described in PCT applications numbers GB 92/01449 and GB 93/02605, was suspended in 1: 1 aq. methanol (40mi) and hydrogenated in a Parr apparatus in the presence of 10% Pd-C (0.4g). After 2h, when uptake appeared complete, the mixture was filtered through celite and the precipitate washed well with the same solvent. The combined filtrate and washings were evaporated to a thick gum (2.1g) which was dissolved in warm water (10ml), diluted to 50ml with warm methanol and tittered. After cooling the colourless prisms were filtered off, washed with methanol and dried to give the product (1.86g, 93% in two crops), m. p. >260°C (dec) (Found : C, 55.7; H, 7.3; N 2.5.

C23H29NOg. CH3OH. H2O requires C, 56.1; H, 6.8; N 2.7%); 5 (D2O), interälia, 0.90 (1 H, s), 1.83 (1 H, m), 2.05, (1 H, dt), 2.35 (1 H, m), 2.82

(3 H, s), 3.57 (1 H, d), 3.80 (1 H, m), 4.12 (1 H, m), 4.47 (1 H, d), 4.86 1 H, d), 6.65 and 6.74 (2 H, 2 d) ; m/z (E. I.) 463 (M+). HPLC area purity 99.6%.

The compound of the invention was compared with some other similar morphine analogues.

Table 1

Substituents, Receptor t Invivo antinociceptive binding (A. U. C.) * Cmpd nitrogen C6 C7-C8 1mg 2mg 4mg 8mg 1 methyl OH unsat 1.0 197.3 241.4 738.3 2 methyl glucuronide unsat 1.88 209.6 618.1 3 methyl A*' unsat 1.73 205.0 168.5 175.5 glucuronide 4 methyl riburonide unsat 2.06 238.1 68.3 5 H glucuronide unsat 1.26 65.6 564.8 837.9 6 methyl glucuronide hydrogenated 0.32 277.4 720.4 753.3 t IC50 relative to morphine. The IC50 is the amount of compound which displaces 50% of a labelled competitive ligand from, u1 binding sites.

*A. U. C. = area under the time-effect curve.

In Table 1, compound 1 is morphine, compound 2 is morphine-6-

glucuronide, and compound 6 is the compound of the present invention.

Compounds 3 and 4 were prepared by a method analogous to that described above for compound 6; compound 5 required removal of the N-methyl group prior to hydrolysis of the protecting groups.

The results in Table 1 show that the compound of the present invention has the greatest binding affinity to the relevant receptor (, u1) (lowest tCgo value relative to morphine), and has the greatest potency in an in-vivo model system of antinociceptive activity.