The present invention relates to 3β,28-diacetoxy-18-oxo-19,20,21,29,30-pentanorlupan-22-oic acid methanol solvate, its use in medicine and processes for its preparation.

FIELD OF THE INVENTION

The present invention relates to 3β,28-diacetoxy-18-oxo-19,20,21,29,30-pentanorlupan-22-oic acid methanol solvate, its use in medicine and processes for its preparation.

BACKGROUND OF THE INVENTION

The compound 3β,28-diacetoxy-18-oxo-19,20,21,29,30-pentanorlupan-22-oic acid was first described in Chem. Listy 91, 1005 (1997), {hacek over (S)}arek J. et al. Its molecular formula may be represented as:

This compound has recently shown promise in the treatment of proliferative disorders such as cancers and leukaemias.

Accordingly there is a need for improved forms of this compound having improved properties as well as new processes for its manufacture and the manufacture of its process intermediates.

SUMMARY OF THE INVENTION

We have now surprisingly found that crystals of 3β,28-diacetoxy-18-oxo-19,20,21,29,30-pentanorlupan-22-oic acid grown from a CHCl3/EtOAc/MeOH solvent system affords a new and improved form of 3β,28-diacetoxy-18oxo-19,20,21,29,30-pentanorlupan-22-oic acid identified as 3β,28-diacetoxy-18-oxo-19,20,21,29,30-pentanorlupan-22-oic acid methanol solvate.

Thus, in a first aspect the present invention provides 3β,28-diacetoxy-18-oxo-19,20,21,29,30-pentanorlupan-22-oic acid methanol solvate. In particular, the present invention provides 3β,28-diacetoxy-18-oxo-19,20,21,29,30-pentanorlupan-22-oic acid•1.5MeOH.

3β,28-diacetoxy-18-oxo-19,20,21,29,30-pentanorlupan-22-oic acid•1.5MeOH may possess one or more of the following advantages as compared to the non-solvated precursor: improved aqueous solubility, uniform size distribution, filtration and drying characteristics, stability (thermal or long term storage), flowability, handling characteristics, isolation and purification characteristics, and physical properties advantageous to formulatory requirements e.g. compressibility.

DETAILED DESCRIPTION OF THE INVENTION

Thus in a further aspect the present invention provides 3β,28-diacetoxy-18-oxo-19,20,21,29,30-pentanorlupan-22-oic acid methanol solvate having at least X-ray diffraction peaks at 14.7 and 16.0. Preferably the powder X-ray diffraction pattern will have peaks at 14.7, 16.0, 16.7, 18.8, 8.3, 20.4, 22.7. More preferably, the powder X-ray diffraction pattern will have peaks at 14.7, 16.0, 16.7, 14.4, 18.8, 8.3, 20.4, 15.7, 22.7. Most preferably, the X-ray diffraction pattern will be substantially as described inFIG. 2.

The unit cell dimension for 3β,28-diacetoxy-18-oxo-19,20,21,29,30-pentanorlupan-22-oic acid•1.5MeOH were determined as described in the examples.

Thus in a further aspect the present invention provides 3β,28-diacetoxy-18-oxo-19,20,21,29,30-pentanorlupan-22-oic acid methanol solvate having unit cell dimensions a=(7).4459(9) Å, α=90°, b=11.0454(9) Å, β=94.002(11)°, c=36.178(4) Å, γ=90°.

The atomic co-ordinates for 3β,28-diacetoxy-18-oxo-19,20,21,29,30-pentanorlupan-22-oic acid•1.5MeOH were determined as described in the examples.

Thus in a further aspect the present invention provides 3β,28-diacetoxy-18-oxo-19,20,21,29,30-pentanorlupan-22-oic acid methanol solvate having atomic co-ordinates substantially as set down in Table 2.

Analysis of the 3β,28-diacetoxy-18-oxo-19,20,21,29,30-pentanorlupan-22-oic acid•1.5 MeOH revealed it to be a monoclinic crystalline form.

Thus, in a further aspect the present invention provides crystalline 3β,28-diacetoxy-18-oxo-19,20,21,29,30-pentanorlupan-22-oic acid methanol solvate wherein the crystalline form is monoclinic.

3β,28-diacetoxy-18-oxo-19,20,21,29,30-pentanorlupan-22-oic acid methanol solvate may be presented as salts or esters, in particular pharmaceutically acceptable salts or esters.

Pharmaceutically acceptable salts of 3β,28-diacetoxy-18-oxo-19,20,21,29,30-pentanorlupan-22-oic acid methanol solvate include suitable acid addition or base salts thereof. A review of suitable pharmaceutical salts may be found in Berge et al, J Pharm Sci, 66, 1-19 (1977). Suitable salts according to the invention include those formed with both organic and inorganic acids and bases. Pharmaceutically acceptable acid addition salts include those formed from hydrochloric, hydrobromic, sulphuric, citric, tartaric, phosphoric, lactic, pyruvic, acetic, trifluoroacetic, succinic, oxalic, fumaric, maleic, oxaloacetic, methanesulphonic, ethanesulphonic, p-toluenesulphonic, benzenesulphonic and isethionic acids. Pharmaceutically acceptable base salts include ammonium salts, alkali metal salts such as those of sodium and potassium, alkaline earth metal salts such as those of calcium and magnesium and salts with organic bases such as dicyclohexyl amine and N-methyl-D-glucamine.

Esters are formed either using organic acids or alcohols/hydroxides, depending on the functional group being esterified. Organic acids include carboxylic acids, such as alkanecarboxylic acids of 1 to 12 carbon atoms which are unsubstituted or substituted (e.g., by halogen), such as acetic acid; with saturated or unsaturated dicarboxylic acid, for example oxalic, malonic, succinic, maleic, fumaric, phthalic or tetraphthalic; with hydroxycarboxylic acids, for example ascorbic, glycolic, lactic, malic, tartaric or citric acid; with aminoacids, for example aspartic or glutamic acid; with benzoic acid; or with organic sulfonic acids, such as (C1-C4)-alkyl- or aryl-sulfonic acids which are unsubstituted or substituted (for example, by a halogen) such as methane- or p-toluene sulfonic acid. Suitable hydroxides include inorganic hydroxides, such as sodium hydroxide, potassium hydroxide, calcium hydroxide, aluminium hydroxide. Alcohols include alkanealcohols of 1-12 carbon atoms which may be unsubstituted or substituted, e.g. by a halogen).

The invention includes all enantiomers and tautomers of 3β,28-diacetoxy-18-oxo-19,20,21,29,30-pentanorlupan-22-oic acid methanol solvate. The man skilled in the art will recognise that 3β,28-diacetoxy-18-oxo-19,20,21,29,30-pentanorlupan-22-oic acid methanol solvate possess optical properties (one or more chiral carbon atoms) and tautomeric characteristics. The corresponding enantiomers and/or tautomers may be isolated/prepared by methods known in the art.

The invention furthermore relates to 3β,28-diacetoxy-18-oxo-19,20,21,29,30-pentanorlupan-22-oic acid methanol solvate in its various crystalline and polymorphic and (an)hydrous forms.

Thus, the present invention further provides a pharmaceutical composition comprising 3β,28-diacetoxy-18-oxo-19,20,21,29,30-pentanorlupan-22-oic acid methanol solvate or pharmaceutically acceptable salt or esters thereof, together with at least one pharmaceutically acceptable excipient, diluent or carrier.

By way of example, in the pharmaceutical compositions of the present invention, 3β,28-diacetoxy-18-oxo-19,20,21,29,30-pentanorlupan-22-oic acid methanol solvate may be admixed with any suitable binder(s), lubricant(s), suspending agent(s), coating agent(s), and/or solubilising agent(s). Examples of such suitable excipients for the various different forms of pharmaceutical compositions described herein may be found in the “Handbook of Pharmaceutical Excipients, 2ndEdition, (1994), Edited by A Wade and P J Weller.

As mentioned previously, 3β,28-diacetoxy-18-oxo-19,20,21,29,30-pentanorlupan-22-oic acid has recently shown promise in the treatment of proliferative disorders such as cancers and leukaemias. Accordingly, in another aspect the present invention provides 3β,28-diacetoxy-18-oxo-19,20,21,29,30-pentanorlupan-22-oic acid methanol solvate for use in therapy, in particular for use in the manufacture of a medicament for the treatment of proliferative disorders such as cancers and leukaemias.

In the alternative, the present invention provides a method of treating proliferative disorders, preferably cancer and/or leukaemia, in a mammal, including a human, which comprises administering an effective amount of 3β,28-diacetoxy-18-oxo-19,20,21,29,30-pentanorlupan-22-oic acid methanol solvate to said mammal.

The present invention also encompasses pharmaceutical compositions comprising 3β,28-diacetoxy-18-oxo-19,20,21,29,30-pentanorlupan-22-oic acid methanol solvate. In this regard, and in particular for human therapy, even though 3β,28-diacetoxy-18-oxo-19,20,21,29,30-pentanorlupan-22-oic acid methanol solvate (including its pharmaceutically acceptable salts, esters and pharmaceutically acceptable solvates) may be administered alone, it will generally be administered in admixture with a pharmaceutical carrier, excipient or diluent selected with regard to the intended route of administration and standard pharmaceutical practice.

For oral administration, particular use is made of compressed tablets, pills, tablets, gellules, drops, and capsules. Preferably, these compositions contain from 1 to 250 mg and more preferably from 10-100 mg, of active ingredient per dose.

Other forms of administration comprise solutions or emulsions which may be injected intravenously, intraarterially, intrathecally, subcutaneously, intradermally, intraperitoneally or intramuscularly, and which are prepared from sterile or sterilisable solutions. The pharmaceutical compositions of the present invention may also be in form of suppositories, pessaries, suspensions, emulsions, lotions, ointments, creams, gels, sprays, solutions or dusting powders.

An alternative means of transdermal administration is by use of a skin patch. For example, the active ingredient can be incorporated into a cream consisting of an aqueous emulsion of polyethylene glycols or liquid paraffin. The active ingredient can also be incorporated, at a concentration of between 1 and 10% by weight, into an ointment consisting of a white wax or white soft paraffin base together with such stabilisers and preservatives as may be required.

Injectable forms may contain between 10-1000 mg, preferably between 10-250 mg, of active ingredient per dose.

Compositions may be formulated in unit dosage form, i.e., in the form of discrete portions containing a unit dose, or a multiple or sub-unit of a unit dose.

A person of ordinary skill in the art can easily determine an appropriate dose of one of the instant compositions to administer to a subject without undue experimentation. Typically, a physician will determine the actual dosage which will be most suitable for an individual patient and it will vary with the age, weight and response of the particular patient. The dosages disclosed herein are exemplary of the average case. There can of course be individual instances where higher or lower dosage ranges are merited, and such are within the scope of this invention.

In an exemplary embodiment, one or more doses of 10 to 150 mg/day will be administered to the patient for the treatment of an antiproliferative disorder.

In a particularly preferred embodiment, the one or more compounds of the invention are administered in combination with one or more other anticancer agents, for example, existing anticancer drugs available on the market. In such cases, the compounds of the invention may be administered consecutively, simultaneously or sequentially with the one or more other anticancer agents.

Anticancer drugs in general are more effective when used in combination. In particular, combination therapy is desirable in order to avoid an overlap of major toxicities, mechanism of action and resistance mechanism(s). Furthermore, it is also desirable to administer most drugs at their maximum tolerated doses with minimum time intervals between such doses. The major advantages of combining chemotherapeutic drugs are that it may promote additive or possible synergistic effects through biochemical interactions and also may decrease the emergence of resistance in early tumor cells which would have been otherwise responsive to initial chemotherapy with a single agent. An example of the use of biochemical interactions in selecting drug combinations is demonstrated by the administration of leucovorin to increase the binding of an active intracellular metabolite of 5-fluorouracil to its target, thymidylate synthase, thus increasing its cytotoxic effects.

Numerous combinations are used in current treatments of cancer and leukemia. A more extensive review of medical practices may be found in “Oncologic Therapies” edited by E. E. Vokes and H. M. Golomb, published by Springer.

Beneficial combinations may be suggested by studying the growth inhibitory activity of the test compounds with agents known or suspected of being valuable in the treatment of a particular cancer initially or cell lines derived from that cancer. This procedure can also be used to determine the order of administration of the agents, i.e. before, simultaneously, or after delivery. Such scheduling may be a feature of all the cycle acting agents identified herein.

3β,28-diacetoxy-18-oxo-19,20,21,29,30-pentanorlupan-22-oic acid methanol solvate may be prepared by crystallising 3β,28-diacetoxy-18-oxo-19,20,21,29,30-pentanorlupan-22-oic acid from a CHCl3/EtOAc/MeOH solvent system.

Thus in a further aspect the present invention provides a process for preparing 3β,28-diacetoxy-18-oxo-19,20,21,29,30-pentanorlupan-22-oic acid methanol solvate which comprises crystallising 3β,28-diacetoxy-18-oxo-19,20,21,29,30-pentanorlupan-22-oic acid from a CHCl3/EtOAc/MeOH solvent system. 3β,28-diacetoxy-18-oxo-19,20,21,29,30-pentanorlupan-22-oic acid (7) may be prepared from betulin (1) according to Scheme 1 set out below.

Essentially the process entails oxidative degradation of the lupane cyclopentane ring is such a way as to install the requisite β-ketoacid group in (7). After acetylation of the betulin hydroxyl groups, the olefin function of diacetate (2) is shifted to the thermodynamically more favourable position in (3) by rearrangement of carbocation intermediates. Subsequent oxidations then yield mono- and di-ketones (4) and (5). Finally, Baeyer-Villiger oxy-insertion of diketone (5) furnishes anhydride (6), whose olefin function is cleaved oxidatively with concomitant hydrolysis of the anhydride group to afford ketoacid (7). The chemical yields of the isolated products (2)-(7) were 96, 64, 100, 94, 95, and 51%, respectively. The cumulative yield for the overall transformation from (1) to (7) was thus ca. 28%. Only a single chromatographic step is required during the reaction sequence, i.e. purification of the final product (7).

The oxidative cleavage of anhydride (6) to ketoacid (7) has been reported, although no details were provided (Sarek, J.; Klinot, J.; Klinotova, E.; Sejbal, J.Chemicke Listy1997, 11, 1005-1006): apparently, an ethyl acetate/water two-phase system with ruthenium (VIII) tetroxide (RuO4), generated in situ from ruthenium(IV) oxide (RuO2) with sodium periodate (NaIO4), was adopted. Oxidative olefin cleavage with the aid of RuO4has been known for some time (Lee, D. G.; van den Engh, M. InOxidation in Organic Chemistry. Trahanovsky, W. S., Ed. Academic Press: New York, 1973. Part B, Chapter 4). These reactions are usually carried out using a catalytic amount of Ru2O, which is oxidised in the aqueous phase by IO4−to RuO4. The latter species is soluble in organic solvents and thus passes into the organic phase, where it oxidises the substrate and itself is reduced back to Ru2O. Providing excess IO4−in the aqueous phase thus ensures continuous regeneration of the reactive ruthenium species. However, we have observed this catalyst re-cycling reaction with (6) failing using various different commercial preparations of anhydrous RuO2or hydrates (RuO2.xH2O) and adopting aqueous two-phase systems with halogenated solvents or ethyl acetate. Exploratory experiments using homogeneous reaction in carbon tetrachloride with freshly prepared solutions of RuO4(preparation as described in: Fieser, L. F.; Fieser, M.Reagents for Organic Synthesis. John Wiley & Sons: New York, 1967. Vol. 1, p 986) have demonstrated that the oxidative olefin cleavage is feasible in principle but is difficult to drive to completion and various by-products were formed. Catalyst inactivation is frequently encountered in this reaction and incorporation of the water-miscible organic solvent acetonitrile into the standard carbon tetrachloride/water system in the ratio 2:2:3 MeCN/CCl4/H2O) has been shown to alleviate this problem in many cases (Carlsen, P. H. J.; Katsuki, T.; Martin, V. S.; Sharpless, K. B.J Org Chem. 1981, 46, 3936-8). Using this system we have now observed the desired reaction on substrate (6) but conversion was still very sluggish and complex reaction mixtures were obtained. Substituting ethyl acetate for carbon tetrachloride and ruthenium (III) chloride (RuCl3) for RuO2has resulted in both a more rapid and cleaner reaction; in particular, fewer polar impurities were formed under these conditions.

Accordingly, in a further aspect the present invention provides a process for the preparation of 3β,28-diacetoxy-18-oxo-19,20,21,29,30-pentanorlupan-22-oic acid (7) which comprises reacting the anhydride of 3β,28-diacetoxy-21,22-secolup-18-ene-21,22-dioic acid (6) with ruthenium (III) chloride and NaIO4in a MeCN/EtOAc/H2O solvent system and optionally converting the resultant 3β,0,28-diacetoxy-18-oxo-19,20,21,29,30-pentanorlupan-22-oic acid to 3β,28-diacetoxy-18-oxo-19,20,21,29,30-pentanorlupan-22-oic acid methanol solvate as described above.

Furthermore, a new purification regimen for the material obtained from the above process comprising: chromatographic separation (SiO2/CH2Cl2MeCN); washing with MeCN; and/or treatment with acetone has resulted in 3β,28-diacetoxy-18-oxo-19,20,21,29,30-pentanorlupan-22-oic acid (7) of >90% purity.

Accordingly, in a further aspect the present invention provides 3β,28-diacetoxy-18-oxo-19,20,21,29,30-pentanorlupan-22-oic acid in substantially pure form.

The term “substantially pure” as used herein in the context of 3β,28-diacetoxy-18-oxo-19,20,21,29,30-pentanorlupan-22-oic acid means material of >90% purity, preferably of >95% purity, more preferably of >97% purity, even more preferably of >99% purity.

Furthermore, material isolated from the new purification regimen may provide 3β,28-diacetoxy-18-oxo-19,20,21,29,30-pentanorlupan-22-oic acid acetonitrile solvate or 3β,28-diacetoxy-18-oxo-19,20,21,29,30-pentanorlupan-22-oic acid acetone solvate or a combination of solvates.

Accordingly, in a further aspect the present invention provides 3β,28-diacetoxy-18-oxo-19,20,21,29,30-pentanorlupan-22-oic acid acetonitrile solvate or 3β,28-diacetoxy-18-oxo-19,20,21,29,30-pentanorlupan-22-oic acid acetone solvate or a mixture thereof.

Furthermore, where the solvent used in the preparation of 3β,28-diacetoxy-18-oxo-19,20,21,29,30-pentanorlupan-22-oic acid is ethanol or iso-propanol or the like the corresponding solvates may be formed.

New solvates of 3β,28-diacetoxy-18-oxo-19,20,21,29,30-pentanorlupan-22-oic acid disclosed herein may possess one or more of the following advantages as compared to the non-solvated precursor: improved aqueous solubility, uniform size distribution, filtration and drying characteristics, stability (thermal or long term storage), flowability, handling characteristics, isolation and purification characteristics, physical properties advantageous to formulatory requirements e.g. compressibility.

Oxidation of (3) with chromium (VI) oxide (chromic anhydride, CrO3) in aqueous acetic acid at room temperature for 12 h was reported (Sejbal, J.; Klinot, J.; Budesinsky, M.; Protiva, J.Collect. Czech Chem. Commun. 1991, 56, 2936-2949). A mixture of products was obtained from which ketone (4) was isolated in 30% yield after chromatography. We have found that superior results are obtained if the oxidation is carried out with a slight molar excess of sodium dichromate (Na2Cr2O7) in a toluene/acetic acid/acetic anhydride solvent system containing sodium acetate at 60° C. Under these conditions crude ketone (4), suitable for further transformation, is obtained in quantitative yield after partitioning of the reaction mixture between water and ethyl acetate, followed by further washing of the organic fraction, drying, and evaporating. Furthermore, pure (4) could readily be obtained without recourse to chromatography simply by crystallisation from methanol. This procedure yields (4) of higher purity than previously reported (m.p. 207-208 versus 198-201° C. in Seijbal et al. cited above).

Thus, in a further aspect the present invention provides a process for the preparation of 21-oxo-lup-18-ene-3β,28-diyl diacetate (4) which comprises reacting lup-18-ene-3β,28-diyl diacetate (3) with sodium dichromate (Na2Cr2O7) and sodium acetate wherein the sodium dichromate (Na2Cr2O7) is present in a slight molar excess. Preferably the reaction is carried out in a toluene/acetic acid/acetic anhydride solvent system. Preferably the reaction is carried out at elevated temperature, more preferably at about 60° C.

The present invention also provides a process for the preparation of 3β,28-diacetoxy-18-oxo-19,20,21,29,30-pentanorlupan-22-oic acid (7) which comprises oxidising lup-18-ene-3β,28-diyl diacetate (3) with a slight molar excess of sodium dichromate (Na2Cr2O7) as described above and converting the resultant 21-oxo-lup-18-ene-3β,28-diyl diacetate (4) to 3β,28-diacetoxy-18-oxo-19,20,21,29,30-pentanorlupan-22-oic acid (7) as described above and optionally converting the 3β,28-diacetoxy-18-oxo-19,20,21,29,30-pentanorlupan-22-oic acid to 3β,28-diacetoxy-18-oxo-19,20,21,29,30-pentanorlupan-22-oic acid methanol solvate.

Acid-catalysed isomerisation of (2) to (3) has been described (Suokas, E.; Hase, T.Acta Chem. Scand. B1975, 29, 139-140). A system consisting of hydrobromic acid, acetic acid, and acetic anhydride in benzene was employed and a correlation in terms of formation of (3) between reaction time and HBr concentration was noted. Performing the reactions at ambient temperature, optimal yields (70-87%) of (3) were reported with reaction times of 18 h to (2) weeks, depending on acid strength (1.1-1.6 M HBr). Similar results were reported elsewhere (Sejbal, J.; Klinot, J.; Vystrcil, A. Collect.Czech Chem. Commun. 1987, 52, 487-492). We have found that elevated reaction temperatures permit shortening of the reaction time. Thus at 90° C., the optimal temperature found, reaction times of 2-4 h are sufficient to achieve complete conversion of (2) with >70% content of (3) in the product (by NMR analysis of crude reaction product after evaporation of solvents). At this temperature, an HBr concentration of 0.9 M was found optimal (using 2.6 M Ac2O and ca. 4 M AcOH in toluene); small deviations in HBr concentration in either direction led to significantly lower yields. In this system a substrate (2) concentration of ca. 0.24 M can be achieved while maintaining a homogeneous reaction. The most effective solvent for the crystallisation from evaporation residues and recrystallisation of (3) was found to be ethyl acetate; employment of this isolation solvent obviates chromatographic purification.

Thus, in a further aspect the present invention provides a process for the preparation of lup-18-ene-3β,28-diyl diacetate (3) which comprises isomerizing lup-20(29)-ene-3β,28-diyl diacetate (2) in a benzene/acetic acid/acetic anhydride solvent system at elevated temperature wherein the concentration of HBr is between about 0.8 and about 1.0M, preferably between about 0.85 and about 0.95M, most preferably about 0.9M. Preferably the reaction is carried out at about 90° C.

In a further aspect the present invention also provides a process for isolating and/or purifying lup-18-ene-3β,28-diyl diacetate (3) which comprises crystallising or recrystallising crude lup-18-ene-3β,28-diyl diacetate (3) from ethyl acetate.

Betulin (1) is a pentacyclic triterpene isolated from birch bark (for review, see, e.g., Hayek, E. W. H.; Jordis, U.; Moche, W.; Sauter, F.Phytochem. 1989, 28, 2229-2242). It can be acetylated to afford the diacetate (2) as described (see, e.g., Tietze, L. F.; Heinzen, H.; Moyna, P.; Rischer, M.; Neunaber, H.Liebigs Ann. Chem. 1991, 1245-1249). We have found that the reaction yield of (2) is highly dependent on the quality of betulin (1) employed. Thus material of >97% purity permits practically quantitative yields of (2), while application of lower grade (1), e.g. commercial materials with purity of <95%, results in <75% yields of (2). Betulin (1) can be purified chromatographically or by recrystallisation from various solvent systems (see, e.g., Eckerman, C.; Ekman, R.Paperi ja Puu1985, 67(3), 100-106). We have found that diacetate (2) can be isolated by precipitation from methanol after evaporation of the acetylation reaction mixture. Material thus isolated is suitable for direct application in the next reaction step.

Thus in a further aspect the present invention provides a (commercial) process for the preparation of lup-20(29)-ene-3β,28-diyl diacetate (2) which comprises reacting substantially pure betulin with acetic anhydride and a base, preferably pyridine, and isolating the crude product by precipitation from methanol.

In a further aspect the present invention also provides the use of substantially pure betulin for the (commercial) manufacture of 3β,28-diacetoxy-18-oxo-19,20,21,29,30-pentanorlupan-22-oic acid (7) and/or 3β,28-diacetoxy-18-oxo-19,20,21,29,30-pentanorlupan-22-oic acid methanol solvate.

The term “substantially pure betulin” as used herein means material of >95% purity, preferably of >97%, more preferably of >99% purity i.e. betulin having respectively less than 5%, preferably less than 3%, more preferably less than 1% of non-betulin material present.

The present invention is further described by way of example.

EXAMPLES

Nomenclature

The compounds are named as derivatives of the natural product lupane and the numbering convention for the C atoms is as follows:

General

3β,28-diacetoxy-18-oxo-19,20,21,29,30-pentanorlupan-22-oic acid (7) (ca. 20 mg) was dissolved in 2 mL of CHCl3/EtOAc (1:1, v/v). The solution was filtered and the filtrate was concentrated to half the original volume. An open-top vial containing this solution was then placed into a larger container charged with a mixture of petroleum spirit (40-60° C. fraction) and methanol (ca. 5:1, v/v). The outer container was sealed and allowed to stand at ambient temperature (ca. 23° C.). After 3 days crystals had formed as colourless needles of 3β,28-diacetoxy-18-oxo-19,20,21,29,30-pentanorlupan-22-oic acid•1.5 MeOH. These were used for X-ray crystal structure analysis.

Crystal structure determination of 3β,28-diacetoxy-18-oxo-19,20,21,29,30-pentanorlupan-22-oic Acid•1.5MeOH

Single crystals of 3β,28-diacetoxy-18-oxo-19,20,21,29,30-pentanorlupan-22-oic acid•1.5MeOH were prepared as described above. Diffraction data were collected on a Stoe Stadi-4 diffractometer equipped with an Oxford Cryosystems low-temperature device operating at 150 K. An absorption correction was applied by Gaussian integration following optimisation of the crystal shape and dimensions against Ψ-scan data. The six most enantiosensitive reflections were 120; 146; 22,10; 14,15; 150 and 224. These, their Laue equivalents and their Friedel opposites were re-measured at opposing values of 2θ extremely carefully and included in the data set used for refinement. A set of crystal data is shown in Table 1. The structure was solved by direct methods and refined by full-matrix least-squares against F2(SHELXTL), to reveal an asymmetric unit consisting of two molecules of (7) and three molecules of methanol of solvation. One carboxylic acid group is disordered via a two-fold rotation about the C—C bond. H-atoms were placed in ideal positions and allowed to ride on their parent atoms. All non-H atoms were refined with anisotropic displacement parameters to yield a final conventional R-factor of 3.63%. Refinement with statistical weights [w=1/σ2(F2)] gave a final Flack parameter of −0.05(9). The signs of the observed and calculated Bijvoet differences were the same for all six sensitive reflections. Taken with the known chiral purity of the sample (refer chromatographic and spectroscopic data above), these data confirm the absolute structure of (7) as shown. The chemical connectivity of (7) was clearly established to be as proposed. The structures of the two independent molecules (FIG. 1) do not differ, except for the disorder in one of the carboxyl groups. In addition to (7) there are three crystallographically independent molecules of methanol of solvation; packing is dominated by H-bond formation between these and the carboxyl groups of the (7) molecules. Bond lengths and angles adopt normal values Table 3; H-bond parameters are listed in Table 6; atomic coordinates are given in Table 2; anisotropic displacement parameters are listed in Table 4; and hydrogen coordinates (×104) and isotropic displacement parameters are set out in Table 5. The powder diffraction pattern for (7) was calculated from the cell parameters and intensity data collected during this single crystal study. A plot of this is shown inFIG. 2.

TABLE 2Atomic coordinates (×104), equivalent isotropic displacementparameters (Å2× 103) and site occupancies. U(eq) isdefined as one third of the trace of the orthogonalizedUij tensor.AtomxyzU(eq)OccO115250(2)1190(2)−1514(1)48(1)1C116696(3)1412(2)−1356(1)33(1)1C2118952(3)2392(2)−1719(1)46(1)1O22110561(2)2195(2)−1913(1)48(1)1O23110804(3)4195(2)−1991(1)58(1)1C23111371(3)3183(2)−2038(1)42(1)1C24113009(3)2848(3)−2231(1)53(1)1C218442(3)1186(2)−1553(1)35(1)1C2518000(5)66(7)−1820(2)36(1)0.67(2)O2617639(5)431(7)−2162(1)52(2)0.67(2)O2717952(5)−967(5)−1718(2)55(1)0.67(2)C25′17869(11)585(11)−1923(3)29(2)0.33(2)O26′17977(9)−590(10)−1874(4)39(2)0.33(2)O27′17362(11)1098(12)−2210(2)58(2)0.33(2)C319967(2)696(2)−1283(1)30(1)1C4110054(2)1313(2)−905(1)26(1)1C518259(2)1248(2)−718(1)21(1)1C5117677(2)−96(2)−705(1)28(1)1C618406(2)1846(1)−318(1)21(1)1C6119263(2)3110(2)−340(1)29(1)1C719628(2)1064(2)−55(1)25(1)1C819595(2)1417(2)353(1)26(1)1C917677(2)1318(2)477(1)21(1)1C1017582(2)1263(2)907(1)25(1)1C10118596(3)137(2)1057(1)35(1)1C10218394(2)2366(2)1115(1)32(1)1C1115587(2)1076(2)978(1)26(1)1O11115393(2)1160(1)1374(1)30(1)1O11213315(3)−310(2)1339(1)63(1)1C11214163(3)449(2)1516(1)37(1)1C11313923(4)752(3)1913(1)57(1)1C1214322(2)1989(2)788(1)28(1)1C1314472(2)1974(2)368(1)26(1)1C1416407(2)2224(1)257(1)21(1)1C14116825(2)3569(2)344(1)29(1)1C1516488(2)1907(1)−164(1)21(1)1C1615208(2)2649(2)−427(1)30(1)1C1715024(2)2085(2)−812(1)31(1)1C1816858(2)1966(2)−973(1)26(1)1O124532(2)622(2)6504(1)52(1)1C123111(2)895(2)6342(1)32(1)1C221326(2)684(2)6528(1)30(1)1C212829(3)1916(2)6689(1)36(1)1O222−916(2)1790(1)6831(1)47(1)1O232−485(3)3521(2)7128(1)91(1)1C232−1458(3)2697(2)7037(1)46(1)1C242−3338(4)2521(3)7142(1)72(1)1C2521718(3)−292(2)6828(1)37(1)1O2622044(2)156(2)7163(1)52(1)1O2721751(2)−1350(1)6758(1)52(1)1C32−164(2)202(2)6248(1)28(1)1C42−191(2)835(2)5872(1)25(1)1C521637(2)765(1)5697(1)21(1)1C5122207(2)−580(2)5684(1)25(1)1C621551(2)1371(2)5298(1)21(1)1C612699(2)2633(2)5317(1)30(1)1C72355(2)598(2)5028(1)25(1)1C82433(2)948(2)4622(1)25(1)1C922369(2)852(2)4506(1)22(1)1C1022510(2)804(2)4078(1)26(1)1C10121518(3)−322(2)3922(1)37(1)1C10221733(2)1921(2)3869(1)32(1)1C1124515(2)622(2)4018(1)26(1)1O11124748(2)713(1)3623(1)32(1)1O11226863(2)−741(2)3667(1)61(1)1C11226029(3)23(2)3487(1)40(1)1C11326317(4)362(3)3096(1)61(1)1C1225755(2)1531(2)4215(1)27(1)1C1325569(2)1502(2)4633(1)25(1)1C1423624(2)1758(1)4735(1)22(1)1C14123214(2)3107(2)4650(1)28(1)1C1523491(2)1423(1)5155(1)21(1)1C1624753(2)2152(2)5427(1)28(1)1C1724871(2)1579(2)5812(1)30(1)1C1823011(2)1465(2)5962(1)25(1)1O(1S)3045(2)−1552(2)7659(1)49(1)1C(1S)3003(4)−1056(2)8022(1)53(1)1O(2S)11395(3)6318(2)−2383(1)65(1)1C(2S)9812(4)6433(3)−2616(1)75(1)1O(3S)6530(3)−1480(2)−2551(1)81(1)1C(3S)6678(4)−1336(4)−2937(1)85(1)1