CA2070230C

CA2070230C - Crystalline oxathiolane derivatives

Info

Publication number: CA2070230C
Application number: CA002070230A
Authority: CA
Inventors: Paul Ravenscroft; Tony Gordon Roberts; Paul Evans
Original assignee: Glaxo Group Ltd
Current assignee: ViiV Healthcare UK Ltd
Priority date: 1991-06-03
Filing date: 1992-06-02
Publication date: 2004-08-03
Anticipated expiration: 2012-06-02
Also published as: CA2070230A1; EP0517145A1; CA2311988A1; IE20020782A1; NO301713B1; JPH06211848A; GEP19991834B; NZ242981A; BG60914B1; AU1881092A; GB9111902D0; PT517145E; MX9202619A; IS1867B; DE69232387D1; SG52455A1; KR930000511A; IL102073A; AU656379B2; EP0517145B1

Abstract

(-)-cis-4-Amino-1-(2-hydroxymethyl-1,3-oxathiolan-5-yl)-(1H)-pyrimidin-2-one represented by the compound of Formula (I-1):

Description

r"y CRYSTALLINE OXATI-IIOIANE DERIVATIVES
The present invention relates to nucleoside analogues and their use in medicine. More specifically the invention is concerned with 1,3-oxathiolane nucleoside analogues, particular physical form thereof, pharmaceutical formulations thereof and the use thereof in the treatment of viral infections.
The compound of formula (I) NHZ
N~
O%eN ( (I) HOCI-Iz ~~ O
S
also known as BCH-1.89 or NtiPB-21 has been described as having antiviral activity in particular against the human immunodeficiency viruses (HIV's), the causative agents of AIDS (5th Anti-Aids Conference, Montreal, Canada 5th-9th June 1989:
Abstracts T.CØ1 and M.C.P. 63; European Patent Application Publication No.
0382562). The compound of formula (I) is a racemic mixture of the two enantiomers of formulae (I-1) and (I-2):-NHZ NHZ
f ~ (I-2) / / ~ (I-1) O~N O~_N
fIOCHZ O HOCH~ O
and was described and tested in the form of its racemate. The only compound currently approded for the treatment of conditions caused by HIV is 3'-azido-3'-deoxythymidine (AZT, zidovudine, I3W 509U). However, this compound has a _7_ significant side-effect liability and thus either canna>t be employed or, once employed, may have to be withdrawn in a significant number of patients. There is in consequence a continuing need to provide compounds which are effective against HIV but with a concomitant significantly better therapeutic. index.
Although the enantiomers of the compound of formula (I) are equipotent against HIV the(-)-enantiomer has considerably lower cytotoxicity than the other enantiomer and is thus the preferred compound as an antiviral agent.
The (-)-enantiomer has the chemical name (-)cis-4-Amino-1-(2 hydroxymethyl-1,3-oxathiolan-5-yl)-(1H)- pyrimidin-2-one. It has the absolute stereochemistry of the compound of formula (I-1) which has the name (2R,cis))-amino-1-(2-hydroxymethyl-1,3-oxathiolan-5-yl)-(1H)-pyrimidin-2-one. The .;_ compound is now known as 3TC.
Preferably 3TC will be substantially free of the corresponding (+)-enantiomer, that is to say no more than about S% w,'w of the (+)- e.nantiorner, preferably no more than about 2%, in particular less than about 1 % w/w is present.
International application PCT/GB91/00706, publication no W091/17159 describes the preparation of 3TC, its antiviral activity and its use in medicine. 3TC
is described and prepared in W091/17159 as a freeze dried powder.
We have now found that 3TC can be obtained in crystalline form and exhibits polymorphism.
There is thus provided in a first aspect of the, invention 3TC in crystalline form.
When crystallised from aqueous solution 3TC is obtained in the form of needle-shaped crystals (hereinafter Form I). In this form the crystals are not favoured for pharmaceutical formulation into solid dosage forms because of their physical properties, for example poor rlow characteristics. We have further found that under certain conditions 3TC may he obtained in the form of substantially bipyramidyl crystals (hereinafter Form Il). The crystal habit of Form II has improved flow characteristics and is thus preferred in the manufacture of solid dosage forms. In addition Form I crystals are a less stable polymorphic forms and certain pharmaceutical unit operations such as milling may cause conversion of "'Trademark --Form I to Form II, an undesirable characteristic for manufacture of solid dosage forms.
3TC in the form of bipyramidyl crystals has a melting point of greater than about 1700C, in particular 177-1780C when pure. 3TC in the form of needle-like crystals has a melting point of Less than about 1300C in particular about 124-in pure form.
3TC in Form II exhibits characteristic absorption bands in its infra red (i.r.) spectrum which are absent from the i.r. spectrum of Form I. In particular Form II
exhibits strong absorption bands at 920 and 850 wavenumbers. Further, a characteristic band of Form I at 1110 wavenumbers is absent from the spectrum of Form II.
Form II of 3TC further shows a characteristic endotherm with an onset temperature at 177-1780C in its differential scanning calorimetry (DSC) profile. By contrast Form I shows a characteristic endotherm in its DSC profile with an onset temperature at 124-1270C.
There is thus provided in a further aspect of the invention 3TC in the form of needle shaped crystals.
In a further aspect there is provided 3TC in the form of bipyramidal crystals.
In a yet further aspect of the invention there is provided 3TC in crystalline form and having a melting point of greater than 1700C, in particular 177-1780C. In an alternative aspect there is provided 3TC in crystalline form and having in its DSC
profile an endotherm with an onset temperature of 177-1780C.
In a yet further alternative there is provided 3TC in crystalline form and having absorption bands at about 920 and about 850 wavenumbers in its infra red spectrum. In particular there is provided 3TC in which in addition to absorption bands at these wavenumbers a band at 1110 wavenumbers is substantially absent.
3TC may be obtained from its racemate by resolution by any method known in the art. for the separation of racemates into their constituent enantiomers. In particular 3TC may be obtained from the known racemate by chiral I-IPLC, by enzyme mediated enantioselective catabolism with a suitable enzyme such as cytidine deaminase or by selective enzymatic degradation of a suitable derivative _:~_ using a 5'-nucleotide. Suitable anethods for preparing 3TC are described in W091/17159.
3TC in the form of needle shaped crystals may be obtained by crystallisation of the compound from aqueous solution or by azeotropic distillation with propan-1-ol.
3TC in the form of the preferred bipyramidal shaped crystals may be obtained by recrystallisation from non-aqueous media, in particular a lower {C2_6) alcohol, for example ethanol, IMS (industrial methylated spirit) or propan-1-ol. In a preferred method 3TC in bipyramidal form may be obtained from 3TC in needle form by ageing the latter in Industrial Methylated Spirit (IMS) or ethanol at elevated temperature (e.g.
30-70°, particularly about 50°C) for an appropriate time (e.g.
0.5-3hrs, in particular about 1 hour or more).
Alternatively, 3TC in bipyramidal form may be obtained by heating the compound in needle form above its melting point of 124-127°, in particular above about 170°C, for example above about 177-178°C and allowing the melt to cool.
In a further alternative 3TC in bipyramidal form may be obtained by grinding or milling the compound in the form of needle shaped crystals.
Preferably 3TC is in the form of bipyramidal shaped crystals substantially free of needle crystals. Where these crystals are obtained by recrystallisation or ageing in liquid media the compound will normally be obtained entirely free of needle shaped crystals.
3TC in crystalline form may be used as an antiviral agent as described in WO
91/17159, published November 14, 1991.
3TC in crystalline form may be formulated as a pharmaceutical formulation for use as an antiviral agent as described in W091/17159.
In a further or alternative aspect there is provided a method for the treatment of a viral infection, in particular an infection caused by a retrovirus such as HIV, in a mammal including man comprising administration of an effective amount of (-)-cis-4-amino-1-(2-hydroxymethyl-1,3-oxathiolan-5-yl)-{1H)-pyrimidin-2-one in crystalline form or a pharmaceutically acceptable derivative thereof.
There is also provided in a further or alternative aspect use of the (-)-cis-4-Amino-1-(2-hydroxymethyl-1,3-oxathiolan-5-yi)-( 1 H)-pyrimidin-2-one in crystalline -4a-form or a pharmaceutically acceptable derivative thereof for the manufacture of a medicament for the treatment of a viral infection.
The(-)-cis-4-amino-1-(2-hydroxymethyl-1,3-oxathiolan-5-yl)-( 1 H)-pyrimidin-2-one in crystalline form or a pharmaceutically acceptable derivative thereof is useful in the treatment of AIDS related conditions such as AIDS-related complex (ARC), progressive generalised lymphadenopathy (PGL), AIDS-related neurological conditions (such as dementia or tropical paraperesis), anti-HIV antibody positive and HIV-positive conditions, Kapopsi's sarcoma, thrombocytopenia purpurea and associated opportunistic infections for example Pneumocystis carinii.
The(-)-cis-4-amino-1-(2-hydroxymethyl-1,3-oxathiolan-5-yl)-( 1 H)-pyrimidin-2-one in crystalline form or a pharmaceutically acceptable derivative thereof is also useful in the prevention of progression to clinical illness of individuals who are anti-HIV
antibody or HIV-antigen positive and in prophylaxis following exposure to HIV.
The(-)-cis-4-amino-1-(2-hydroxymethyl-1,3-oxathiolan-5-yl)-( 1 H)-pyrimidin-2-one in crystalline form or a pharmaceutically acceptable derivative thereof may also be used for the prevention of viral contamination of physiological fluids such as blood or semen in vitro.
It will be appreciated by those skilled in the art that reference herein to treatment extends to prophylaxis as well as the treatment of established infections or symptoms.
It will be further appreciated that the amount of the(-)-cis-4-amino-1-(2-hydroxymethyl-1,3-oxathiolan-5-yl)-(1H)-pyrimidin-2-one in crystalline form or a pharmaceutically acceptable derivative thereof required for use in treatment will vary not only with the particular compound selected but also with the route of administration, the nature of the condition being treated and the age and condition of the patient and will ultimately at the discretion of the attendant physician or veterinarian. In general however a suitable dose will be in the range of from about 0.1 to about 750mg/lcg of bodyweight per day preferably in the range of 0.5 to 60 mg/lcg/day, most preferably in the range of 1 to 20mg/kg/day.

-4b-The desired dose may conveniently be presented in a single dose or as divided doses administered at appropriate intervals, for example as two, three, four or more sub-doses per day.
The compound is conveniently administered in unit dosage form; for example containing 10 to 1500mg, conveniently 20 to 1000mg, most conveniently 50 to 700 mg of active ingredient per unit dosage form.
Ideally the active ingredient should be administered to achieve peak plasma concentrations of the active compound of from about 1 to about 75 p.M, preferably about 2 to 50 ~M, more preferably about 3 to about 30 p,M. This may be achieved, for example, by the intravenous injection of a 0.1 to 5°/o solution of the active ingredient, optionally in saline, or orally administered as a bolus containing about 1 to about 100mg of the active ingredient. Desirable blood levels may be maintained by a continuous infusion to provide about 0.01 to about 5.0 mg/kg/hour or by intermittent infusions containing about 0.4 to about 15 mg/kg of the active ingredient.
While it is possible that, for use in therapy, the(-)-cis-4-amino-1-(2-hydroxymethyl-1,3-oxathiolan-5-yl)-(1H)-pyrimidin-2-one in crystalline form or a pharmaceutically acceptable derivative thereof may be administered as the raw chemical it is preferable to formulate it into a pharmaceutical formulation.
The invention thus further provides a pharmaceutical formulation comprising the(-)-cis-4-amino-1-(2-hydroxymethyl-1,3-oxathiolan-5-yl)-(1H)-pyrimidin-2-one in crystalline form or a pharmaceutically acceptable derivative thereof together with one or more pharmaceutically acceptable carriers therefor and, optionally, other therapeutic and/or prophylactic ingredients. The carriers) must be 'acceptable' in the sense of being compatible with the other ingredients of the Formulation and not deleterious to the recipient thereof.
Pharmaceutical formulations include those suitable for oral, rectal, nasal, topical (including buccal and sub-lingual), vaginal or parenteral (including intramuscular, sub-cutaneous and intravenous) administration or in a form suitable for administration by inhalation or insufflation. The formulations may, where appropriate, be conveniently presented in discrete dosage units and may be prepared by any of the methods well -4c-known in the art of pharmacy. All methods include the step of bringing into association the active compound with liquid carriers or finely divided solid carriers or both and the, if necessary, shaping the product into the desired formulation.
Pharmaceutical formulations suitable for oral administration may conveniently be presented as discrete units such as capsules, cachets or tablets each containing a predetermined amount of the active ingredient; as a powder or granules; as a solution, a suspension or as an emulsion. The active ingredient may also be presented as a bolus, electuary or paste. Tablets and capsules for oral administration may contain conventional excipients such as binding agents, fillers, lubricants, disintegrants, or wetting agents. The tablets may be coated according to methods well known in the art. Oral liquid preparations may be in the form of, for example, aqueous or oily suspensions, solutions, emulsions, syrups or elixirs, or may be presented as a dry product for constitution with water or other suitable vehicle before use. Such liquid preparations may contain conventional additives such as suspending agents, emulsifying agents, non-aqueous vehicles (which may include edible oils), or preservatives.
The(-)-cis-4-amino-1-(2-hydroxymethyl-1,3-oxathiolan-S-yl)-( 1 H)-pyrimidin-2-one in crystalline form or a pharmaceutically acceptable derivative thereof may also be formulated for parenteral administration (e.g. by injection, for example bolus injection or continuous infusion) and may be presented in unit dose form in ampoules, pre-filled syringes, small volume infusion or in mufti-dose containers with an added preservative.
The compositions may talce such forms as suspensions, solutions, or emulsions in oily or aqueous vehicles, and may contain formulatory agents such as suspending, stabilising and/or dispersing agents. Alternatively, the active ingredient may be in powder form, obtained by aseptic isolation of sterile solid or by lyophilisation from solution, for constitution with a suitable vehicle, e.g. sterile, pyrogen-free water, before use.
For topical administration to the epidermis the(-)-cis-4-amino-1-(2-hydroxymethyl-1,3-oxathiolan-5-yl)-(1H)-pyrimidin-2-one in crystalline form or a pharmaceutically acceptable derivative thereof may be formulated as ointments, creams or lotions, or as a transdermal patch. Ointments and creams may, for example, be formulated with an aqueous or oily base with the addition of suitable thickening and/or -4d-gelling agents. Lotions may be formulated with an aqueous or oily base and willl in general also contain one or more emulsifying agents, stabilising agents, dispersing agents, suspending agents, thickening agents, or colouring agents.
Formulations suitable for topical administration in the mouth include lozenges comprising active ingredient in a flavoured base, usually sucrose and acacia or tragacanth; pastilles comprising the active ingredient in an inert base such as gelatin and glycerin or sucrose and acacia; and mouthwashes comprising the active ingredient in a suitable liquid earner.
Pharmaceutical formulations suitable for rectal administration wherein the carrier is a solid are most preferably presented as unit dose suppositories. Suitable carriers include cocoa butter and other materials commonly used in the art, and the suppositories may be conveniently formed by admixture of the (-)-cis-4-amino-1-(2-hydroxymethyl-1,3-oxathiolan-5-yl)-(1H)-pyrimidin-2-one in crystalline form or a pharmaceutically acceptable derivative thereof with the softened or melted carriers) followed by chilling and shaping in moulds.
Formulations suitable for vaginal administration may be presented as pessaries, tampons, creams, gels, pastes, foams or sprays containing in addition to the active ingredient such carriers as are known in the art to be appropriate.
For intra-nasal administration the compounds of the invention may be used as a liquid spray or dispersible powder or in the form of drops.
Drops may be formulated with an aqueous or non-aqueous base also comprising one more dispersing agents, solubilishing agents or suspending agents. Liquid sprays are conveniently delivered from pressurized packs.
For administration by inhalation the(-)-cis-4-amino-1-(2-hydroxymethyl-1,3-oxathiolan-5-yl)-(1H)-pyrimidin-2-one in crystalline form or a pharmaceutically acceptable derivative thereof is conveniently delivered from an insufflator, nebuliser or a pressurized pack or other convenient means of delivering an aerosol spray.
Pressurised packs may comprise a suitable propellant such as dichlorodifluoromethane, trichlorofluoromethane, dichlorotetrafluoroethane, carbon dioxide or other suitable gas.

-4e-In the case of a pressurized aerosol the dosage unit may be determined by providing a valve to deliver a metered amount.
Alternatively, for administration by inhalation or insufflation, the(-)-cis-4-amino-1-(2-hydroxymethyl-1,3-oxathiolan-5-yl)-(1H)-pyrimidin-2-one in crystalline form or a pharmaceutically acceptable derivative thereof may take the form of a dry powder composition, for example a powder mix of the compound and a suitable powder base such as a lactose or starch. The powder composition may be presented in unit dosage form in, for example, capsules or cartridges or e.g. gelatin or blister packs from which the powder may be administered with the aid of an inhalator or insufflator.
When desired the above described formulations adapted to give sustained release of the active ingredient may be employed.
The pharmaceutical compositions according to the invention may also contain other active ingredients such as antimicrobial agents, or preservatives.
The compounds of the invention may also be used in combination with other therapeutic agents for example other antinfective agents. In particular the compounds of the invention may be employed together with known antiviral agents.
The invention thus provides, in a further aspect, a combination comprising the(-)-cis-4-amino-1-(2-hydroxymethyl-1,3-oxathiolan-5-yl)-(1H)-pyrimidin-2-one in crystalline form or a pharmaceutically acceptable derivative thereof.compound together with another therapeutically active agent, in particular an antiviral agent.
The combinations referred to above may conveniently be presented for use in the form of a pharmaceutical formulation and thus pharmaceutical formulations comprising a combination as defined above together with a pharmaceutically acceptable carrier therefor comprise a further aspect of the invention.
Suitable therapeutic agents for use in such combination include acyclic nucleosides such as acyclovir or ganciclovir, interferons such as oc, (3 or y-interferon, renal excretion inhibitors such as probenecid, nucleoside transport inhibitors such as dipyridamole, 2',3'-dideoxynucleosides such as AZT, 2',3'-dideoxycytidine, 2',3'-dideoxyadenosine, 2',3'-dideoxyinosine, 2',3'dideoxythymidine, 2',3'-dideoxy-2',3'-didehydrothymidine and 2',3'-dideoxy-2',3'-didehydrocytidine, immunomodulators such - 4f -as interleulcin II (IL2) and granulocyte macrophage colony stimulating factor (GM-CSF), erythropoetin, ampligen, thymomodulin, thymopentin, foscarnet, ribavirin and inhibitors of HIV binding to CD4 receptors e.g. soluble CD4, CD4 fragments, CD4 hybrid molecules, glycosylation inhibitors such as 2-deoxy-D-glucose, castanospermine and I-deoxynoj irimycin.
The individual components of such combinations may be administered either sequentially or simultaneously in separate or combined pharmaceutical formulations.
When the(-)-cis-4-amino-1-(2-hydroxymethyl-1,3-oxathiolan-5-yl)-(1H)-pyrimidin-2-one in crystalline form or a pharmaceutically acceptable derivative thereof is used in combination with a second therapeutic agent active against the same virus the dose of each compound may be either the same as or differ from that when the compound is used alone. Appropriate doses will be readily appreciated by those skilled in the art.
Figure 1 shows 3TC in the form of needle shaped crystals (Form I).
Figure 2 shows 3TC in the form of bipyramidyl shaped crystals (Form II).
Figure 3 is an infra-red spectmm of Form I crystals.
Figure 4 is an infra-red spectrum of Form II crystals.
Figure S is a DSC thermogram of Form I crystals.
Figure 6 is a DSC thermogram of Form II crystals.

_5_ The following examples illustrate Lhe invention but are not intended as a limitation thereof. All temperatures are in UC.

5-Methoxy-1,3-oxathiolane-2-methanol, benzoate.
A solution of zinc chloride (L.6g) in hot methanol (15m1) was added to a stirred solution of mercaptoacetaldehyde, dimethyl acetal (34.2g) and benzoyloxy acetaldehyde (48.3g) in toluene (130Umi) which was then heated to reflux under nitrogen for 50 min. The cooled mixture was concentrated, diluted with some toluene, then filtered through Kiesulguhr. The combined filtrates and toluene were washed with aqueous saturated sodium bicarbonate solution (x2) and brine, dried (MgS04) then evaporated to an oil which was subjECted to column chromatography X
on silica (2kg, Merck 9385 ) eluted with chloroform to give the title product as an oil (45.1g) a mixture of anomers (ca 1:1); 1H NMR (DMSO-d6) 3.1-3.3(4H), 3.42(6H), 4.4-4.6 (4H), 5.41(1H), 5.46 {1H), 5.54 (1H), 5.63 (1I-I;l, 7.46 (4H;), 7.58 (2H), 8.07 (4H);ymax (CHBr3)1717.6cm-1.

( t )-cis-1-(2-Benzoyloxymethy 1-1, 3-oxath iolan-5-yl)-( 1 H)-pyrirnidin-2-4-dione A mixture of finely ground uracil(9.62g) hexamethyl disilazane (50 ml) and ammonium sulphate (30 mg) was heated at reflux under nitrogen until a clear solution was obtained. This was cooled and then evaporated to a colourless oil, which was dissolved, under nitrogen atmosphere, in acetonitrile (100m1). The solution was added to a stirred ice cooled solution of 5-methoxy-1.,3-oxathiolane-2-methanol, benzoate (intermediate 1) (19.43g), in acetonitrile (600m1) and trimethyl silyl trifluoromethanesulphonate (14.7m1) was added. The ice bath was removed, and the solution was heated at refiux under nitrogen for 45 rains. After cooling and evaporation, the residue was purified by column chromatography over lkg of silica gel (Merck 9385) eluting with chloroform/methanol 9:1. Appropriate fractions were cooled and evaporated to afford a crude residue. This was fractionally crystallized from the minimum of hot methanol (c.1200m1) to afford the title compound (6.32g) *Trademark __ as white crystals. 1H NMR( d6DMS0) d 11.36 (lH,bs). 7.50-8.00 (6I-I,m), 6.20 (lH,t), 5.46 (2I-I,m), 4,62 (2H, m), 3.48 (1H, m), 3.25 (lI-I, m).

(t)-(cis -Amino-1- 2-benzoylox~rmethyl-1,3-oxathiolan-5-yl)-(1H)-pyrimidin-2-one Method a A suspension of cytosine (20.705g) and ammanium sulphate (few mgs) in hexamethyldisilazane (110m1) was stirred and heated at reflux for 2lhh, under nitrogen. Solvent was removed by evaporation, and the residual solid was dissolved in dry acetonitrile (350m1). This solution was transferred using flexible needle techniques into a stirred, ice-chilled solution of 5-methoxy-1,3-oxathiolane-2-methanol, benzoate (Intermediate I) (43.57g) in acetonitrile (650m1) under nitrogen.
Trimethylsilyl trifluoromethanesulphonate (33m1) was added, the solution was allowed to warm to ambient temperature (li/zh) then heated to refiux for an overnight period. The residue mixture was concentrated, diluked with saturated aqueous sodium bicarbonate solution (500m1),'then extracted with ethyl acetate (3x500m1). The combined extracts were washed with water (2x250m1) and brine (250m1) dried (MgS04) then evaporated to a foam which was subjected to column chromatography on silica (600g, merck 7734), eluted with ethyl acetate-methanol mixtures to give a mixture of anomers (ca 1:1 31.59g). The mixture was crystallised from water (45m1) and ethanol (9.0m1) to give a solid (10.23g) which was recrystallised from ethanol (120m1) and water (30m1) to give the title product as a white solid (9.26g);amax (MeOH) 229.4mm (E1% 610); 272.4mm (E1%
1cm lcm 293); lI-I NMR (DMSO d6) 8 3.14 (1H), 3.50 (1H), 4.07 (2H), 5.52 (1H), 5.66 (1H), 6.28 (1H), 7.22 (2H), 7.56 (2H), 7.72 (2H), 8.10 (2H).
Method b _7-Phosphorus oxychloride (7.Uml) was added dropwise to a stirred , ice-cooled suspension of 1,2,4-triazole (11.65g) in acetonitrile (120m1) then, keeping the internal temperature below 150C, triethylamine (22.7m1) was added dropwise.
After min a solution of (~)-cis -1-{2-benxoyloxymethyi-1,3-oxathiolan-S-yl)-(1H)-pyrimidin-2,4-dione (Intermediate 2) {6.27g) in acetonitrile (330m1)was slowly added. Stirring was then continued at room temperature overnight. The mixture was cooled by means of an ice bath and triethylamine (30m1) was slowly added followed by water (21m!). The resultant solution was evaporated, and the residue was partitioned between saturated sodium bicarbonate solution (400m1) and chloroform (3x200m1). The combined chloroform extracts were dried and magnesium sulphate, filtered and evaporated to give a crude residue (9.7g).
The residue was dissolved in 1,4-dioxan (240m1) and concentrated aqueous ammonia solution (s.g 0.880, SOmI) was added. After 1'/ztt the solution was evaporated and the residue dissolved in methanol. This caused precipitation of a solid, which was filtered off. The mother liquors were purified by column chromatography over silica gel (Merck 9385, 600g). Appropriate fractions were pooled and evaporated to give the title compound as a fawn solid (2.18g), identical to that obtained by Method (a).

( t )-(cis)-4-Am ino-1-(2-hydroxymethyl-1,3-oxathiolan-5-yi)-( 1 H) _ pyrimidin-2-one A suspension of (cis)-4-amino-1-(2-benzoyloxymethyl-1,3-oxathiolan-S-yl)-(1H)-pyrimidin-2-one (Intermediate 3) (8.19g) and Amberlite IRA-400 (OH) resin (8.24g) in methanol (250m1) was stirred and heated to reflux for 11/ah. Solids were removed by filtration then washed with methanol. The combined filtrates were evaporated. The residue was triturated with ethyl acetate (80m1). The resulting white solid was collected by filtration to give the title product (5.09g), 1H
NMR
(DMSO-d6) 3.04 (1H), 3.40 (1H), 3.73 (2H), 5.18 (iH), 5.29 (1H), 5.73 (1H), 6.21 {1H), 7.19 (2H), 7,81 (1H).

'Trademark _g--)-cis-4-Amino-1-(2-hvdroxvmethvl-1, ~-oxathiolan-S-vll-( 1 H) pvrimidin-2-one (i) Three SOmI flasks of nutrient broth (Oxoid Ltd) were. inoculated with a loopful 7v each of Escherichia coli (ATCC 23~i48) scraped from a Nutrient Agar plate. The flasks were incubated overnight at 3700 with shaking at 2S0 rev/min and then each flask was used to inoculate 41 of CDD medium (glutamic acid, 3811; MgS04, U.2g/1: K2S04, 2.5g/1; NaCl, 2.'3g/1, Na2HP0421-~t20, 1.1g/1, NaH2P042H20 0.6g/1 cytidine, 1.2g/1) in a seven litre fermenter. The cultures were fermented at 750 rev/min, 370C with aeration at 41/min. After growth for 24hrs the cells were collected by centrifugation (SOOOg, 30 minutes) to yield ?2g wet weight. The cell pellet was resuspended in 300m1 of 20mM Tris HCi buffer (pH 7.5) and disrupted by sonication (4 x 45 seconds). The cell debris was removed by centrifugation (30,000 g, 30 minutes) and the protein in the supernatant was precipitated by addition of ammonium sulphate to 75% saturation. The precipitate was collected by centrifugation (30,000g. 30 minutes) and the pellet was resuspended in 25m1 of HEPES buffer (100mM, pH 7.0) containing ammonium sulphate (75% saturation).
Enzyme solution was prepared by centrifugation at 1.2,UU0 rpm for 30 mins. The supernatant was discarded and the pellet dissolved in Tris HCl buffer (pH 7.0;
100mM) to the original volume.
(ii) Intermediate 4 (115mg was dissolved in water (100m1), and stirred. Enzyme solution (O.SmI) was added, and the mixture was maintained at a constant pH by the continual addition of HCl (25mM). The conversion was monitored by chiral HPLC, which showed that the (+) enantiomer of the substrate was preferentially deaminated. After 22hr the (+) enantiomer of the substrate (RT l2.Smin) had been completely removed, and the solution was adjusted to pH 10.5 by the addition of conc. sodium hydroxide.
The solution produced above was eluted through a column of QAE Sephadex (A25; Pharmacia; 30X l.6cm), pre-equilibrated to pHl 1. The column was washed with water (200m1) and then with HCl (0.1M). Fractions (40m1) were taken , and *Trademark 2~3"~~~~~

analysed by reversed phase HPLC. Fractions 5-13, containing the unreacted (-) enantiomer of the substrate, were combined and adjusted to pH 7.5 with HCI.
Fraction 47, containing deaminated product, was adjusted to pH7.5 with dil.
NaOH.
Analysis by chiral HPLC showed that this material was a mixture, consisting of one enantiomer (RT 10.2min) as the major component with the other enantiomer (RT
8.5min) as a minor component (e.e ca 90%).
(iii) Stage (ii) above was repeated on a larger scale . The compound of Example 1 (363rng) in 250m1 of water was incubated with enzyme solution (0.5m1), prepared as in Stage (i). Further aliquots (0.5m1) of enzyme were added after 18 and 47 hrs.
The reaction mixture was stirred for 70hr., then left standing for a further 64hr.
Analysis by chiral hplc indicated that the (+) enantiomer of the substrate had been completely deaminated, and the resulting solution was adjusted to pH10.5 with Na01-1.
The solution above was loaded onto the.same QAE column, and eluted as in stage (i). Fractions 2-6, containing a mixture of the residual substrate and deaminated product, were bulked. Fractions 7-13, containing the residual substrate ((-) ,nantiomer), were bulked and adjusted to pH7.5. Fractions 25-26, containing deaminated product, were bulked and neutralised Fractions 2-6 above were re-eluted through the same QAE column. Fractions 3-11 from this second column contained unrected substrate ((-) enantiomer).
Fraction 70 contained the deaminated product.
(.iv) The resolved substrate fractions from stage (ii) and (iii) were combined and adjusted to pH7.5. This solution was eluted through a column .of XAD-16 (40x2.4cm), packed iW eater. The column was washed with water, and then eluted with acetone: water (1:4 v/v). Fractions containing the desired (-) enantiomer were bulked and freeze-dried to give a white powder (190mg).
The HPLC methods used above were as follows:-1. Reversed Phase analytical HPLC

Column . Capital Cartridge Spherisorb ODS-2 (SuM) 150x4.6mm Eluant . Ammonium dihydrogen phosphate (SOmM)+

5% MeCN

Flow . l.Sm1/min Detection . UV, 270nm Retention Times . BCH 189 S.Smin deaminated BCH -189 8.lmin 2. Chiral analytical HPLC

Column . Cyclobond I Acetyl 250x4.6mm Eluant . 0.2% Triethylammonium acetate (pH7.2) Flow . l.Omlimin Detection . UV, 270nm Retention . BCH 189 11.0 and l2.Smin Times deaminated BCH-189 8.5 and 10.2 min (The:
bioconversion was followed by monitoring the loss of the peak at l2.Smin., and accumulated of product at 10.2min).

Example 1 A suspension of Intermediate 5 (64.8g) in water (20(1mL) was heated to 450 to give a solution. The solution was cooled to 300.
The product crystallised as an unstirrable mass. This was broken up and the suspension stirred at ca. 100 for 1h.
The product was isolated by filtration and washed with ethanol (IMS; 2 x 30mL) then dried in vacuo at 450 for 24h to give 3TC as Form I (fine needle crystals).
*Trademark The compound had an i.r. spectrum and DSC thermograph identical to Figures 3 and 5 respectively.
Example 2 A suspension of the compound of Example 1 (10.0g) in industrial methylated spirits (IMS; 200mL; 20 volumes) was heated to reflux to give a clear solution. The solution was filtered hot and the filtrate was distilled at atmospheric pressure until 100mL (10 volumes) of solution remained. The solution was seeded with authentic material2 and allowed to cool from 800 to 25a over 1h. Crystallis_ation began at 790. The suspension was stirred at I50 for 1h. The product was isolated by filtration and washed with IMS (lOmL; 1 volume). Drying in vacuo at 500 gave the title compound as aggregates of bipyeamides (8.42g) m.p. 179-1810. (-)-cis-4-amino-1-(2-hydroxymethyl-1,3-oxathiolan-5-yl)-(1H)-pyrimidin-2-one.
Assay Found : C,41.9; H,4.85; N,18.35 C8H11N303S requires : C,41.9; H,4.8; N,18.3%
The compound had an i.r. spectrum and DSC thermograph identical to Figures 4 and 6 respectively.
Example 3 A suspension of the product of Example 1 (20.0g) in Industrial Methylated Spirits (IMS; 100mL; S volumes) was stirred slowly at 500 for 1h.
A small sample (ca 100mg) was removed, dried in vacuo at 500 and examined by microscopy and differential scanning calorimetry (DSC).
The sample was 100% Form II (bipyramidal habit).
The suspension was stirred at 500 for a further 2h and a sample removed, Microscopy showed no change.
The suspension was stirred at 500 for 22h, then cooled to 200 and stirred for 1h.
The suspension was filtered, the product washed with iMS (20mL; lvol) and dried in vacuo to give as a white crystalline solid (17.13g) (-)-cis-4-amino-1-(2-hydroxymethyl-1,3-oxathiolan-S-yl)-(1H)-pyramidin-2-one m.p. 180-1810.

Assay Found : C,41.85; H,4.85; N,18.3 C8H11N303S Requires : 0,41.9; H,4.8; N,18.3%
The product had an i.r. spectrum and DSC thermogram identical to those of Figures 4 and 6 respectively.
Example 4 X-Ray Crystallography data for Form II
Crystal Data C8H11N303S, M = 229.26.
Tetragonal, a = b = 8.749(3), c = 26.523(9)A, V= 2030(2)A3 (by least-squares refinement on diffractometer angles for 14 automatically centred reflections, 1 = 1.54184A).
Space group P43212 (No. 96), z = 8, Dc = 1.50g cm-3 F(000) = 960, m(Cu-Ka) = 27.5 cm-1.
Dimensions of data crystal 0.48 x 0.32 x 0.30 mm.
Single crystals of Form II (colourless bipyramids) were examined by X-ray diffraction. A total of 1651 reflections were measured (3 < 2,7 < 1150) on a Siemens R3mN diffractometer with monochromatised Cu-Ka radiation and using 2J/w scans. The structure was solved by direct methods and the non-hydrogen atoms refined anisotropically. The hydrogen atoms attached to carbon were idealised (C-H
= 0.96A) and allowed to ride on their parent carbon atoms. Three Hs on -NH2 and -OH groups were located from a difference Fourier map. All H atoms were refined isotropically. Refinement converged to give R = 0.068, RW = 0.069, W 1 =
[s2(F) +
0.005[F~2). Maximum residual electron density was ().45 eA-3. The absolute chirality was confirmed using Rogers' eta test [h = 0.99 (9)J.
*Trademark Example 5 Pharmaceutical Formulations a 100m~ Tablets Ingredients per tablet 3TC (Form II) 100.Omg Microcrystalline Cellulose NF 189.5mg Sodium Starch Glycolate NF 9.Omg Magnesium Stearate NF 1.5m~
Total Weight 300.Omg The 3TC (Form II), microcrystalline cellulose and sodium starch glycolate were sieved and blended in a V-blender for about 15 minutes. Sieved magnesium stearate was then added and blending continued for a further 2 minutes.
The blend was compressed in standard tabletting equipment and then film coated with an aqueous suspension of grey Opadry to produce aesthetically acceptable tablets.
bbl 300mg Tablets Ingredients per tablet 3TC (Form II) 300.Omg Microcrystalline Cellulose NF 279.Omg Sodium Starch Glycolate NF l8.Orrig Magnesium Stearate NF 1.5m~
Total Weight 600.Omg Tablets were prepared as described in (a) above.

Claims

1. (-)-cis-4-Amino-1-(2-hydroxymethyl-1,3-oxathiolan-5-yl)-(IH)-pyrimidin-2-one in crystalline form.

2. (-)-cis-4-Amino-1-(2-hydroxymethyl-1,3-oxathiolan-5-yl)-(IH)-pyrimidin-2-one in the form of bipyramidal crystals.

3. The crystalline form as claimed in claim 2 having a melting point of greater than 170°C.

4. The crystalline form as claimed in claim 2 or 3, having a melting point of 178°C.

5. The crystalline form as claimed in any one of claims 2 to 4 having absorption bands in its infra-red spectrum of 920 and 850 wave numbers.

6. The crystalline form as claimed in any one of claims 2 to 5 having no absorption band in its infra-red spectrum at 1110 wave numbers.

7. The crystalline form as claimed in any one of claims 2 to 6 having an endotherm with an onset temperature at 177-178°C in its differential scanning calorimetry profile.

8. (-)-cis-4-Amino-1-(2-hydroxymethyl-1,3-oxathiolan-5-yl)-(IH)-pyrimidin-2-one in the form of needle shaped crystals.

9. The crystalline form as claimed in claim 8 having a melting point of less than about 130°C.

10. The crystalline form as claimed in claim 8 or 9 having a melting point of 127°C.

11. The crystalline form as claimed in any one of claims 8 to 10 having an endotherm with an onset temperature of 124-127°C in its differential scanning calorimetry profile.

12. The crystalline form as claimed in any one of claims 8 to 11 having an absorption brand in its infra-red spectrum at about 1110 wave numbers.

13. A method for the preparation of (-)-cis-4-Amino-1-(2-hydroxymethyl-1,3-oxathiolan-5-yl)-(IH)-pyrimidin-2-one in the form of needle shaped crystals which comprises crystallisation of the compound from aqueous solution.

14. A method for the preparation of (-)-cis-4-Amino-1-(2-hydroxymethyl-1,3-oxathiolan-5-yl)-(IH)-pyrimidin-2-one in the form of needle shaped crystals which comprises azeotropic distillation of an aqueous solution of the compound with propan-1-ol.

15. A method for the preparation of (-)-cis-4-Amino-1-(2-hydroxymethyl-1,3-oxathiolan-5-yl)-(IH)-pyrimidin-2-one in the form of bipyramidal shaped crystals which comprises recrystallisation from non-aqueous medium.

16. A method as claimed in claim 15 wherein the non-aqueous medium is a C2-6 alcohol.

17. A method as claimed in either claim 15 or claim 16 wherein the non-aqueous medium is selected from ethanol and industrial methylated spirit.

18. A method for the preparation of (-)-cis-4-Amino-1-(2-hydroxymethyl-1,3-oxathiolan-5-yl)-(IH)-pyrimidin-2-one in the form of bipyramidal crystals which comprises aging the compound in the form of needle shaped crystals in ethanol or industrial methylated spirits at elevated temperature.

19. A pharmaceutical formulation comprising (-)-cis-4-Amino-1-(2-hydroxymethyl-1, 3-oxathiolan-5-yl)-(IH)-pyrimidin-2-one in bipyramidal crystalline form and a pharmaceutically acceptable carrier therefore.

20. A pharmaceutical formulation as claimed in claim 19 in a form suitable for oral administration.

21. A pharmaceutical formulation as claimed in claim 19 or claim 20 in the form of a tablet or capsule.

22. A pharmaceutical composition in solid dosage unit form comprising a therapeutically effective amount of (-)-cis-4-Amino-1-(2-hydroxymethyl-1,3-oxathiolan-5-yl)-(IH)-pyrimidin-2-one in bipyramidal crystalline form as the only active ingredient in combination with a pharmaceutically acceptable carrier therefor.

23. A pharmaceutical composition in solid dosage unit form comprising a therapeutically effective amount of (-)-cis-4-Amino-1-(2-hydroxymethyl-1,3-oxathiolan-5-yl)-(IH)-pyrimidin-2-one in bipyramidal crystalline form in combination with a pharmaceutically acceptable carrier therefor.

24. A pharmaceutical composition according to claim 22 or 23 wherein (-)-cis-4-Amino-1-(2-hydroxymethyl-1,3-oxathiolan-5-yl)-(IH)-pyrimidin-2-one in bipyramidal crystalline form is substantially free of non-crystalline (-)-cis-4-Amino-1-(2-hydroxymethyl-1,3-oxathiolan-5-yl)-(IH)-pyrimidin-2-one.

25. A pharmaceutical composition according to claim 22 or 23 wherein the (-)-cis-4-Amino-1-(2-hydroxymethyl-1,3-oxathiolan-5-yl)-(IH)-pyrimidin-2-one in bipyramidal crystalline form is substantially free of needle crystals of (-)-cis-4-Amino-1-(2-hydroxymethyl-1,3-oxathiolan-5-yl)-(IH)-pyrimidin-2-one.

26. A pharmaceutical composition according to any one of claims 22 to 25 in oral administration form.

27. A method as claimed in claim 18 wherein said elevated temperature is 30°C to 70°C.

28. A method as claimed in claim 18 or 27 wherein the needle shaped crystals are prepared by a method which comprises crystallisation of the compound from aqueous solution.

29. A method as claimed in claim 18 or 27 wherein the needle shaped crystals are prepared by a method which comprises azeotropic distillation of an aqueous solution of the compound with propan-1-ol.