WO2006067412A1 - Chemical processes for the preparation of a colchinol derivative and intermediates - Google Patents

Abstract

A process for the preparation of a colchinol derivative of the Formula (I): wherein each R, which may be the same or different, is selected from (1-6C)alkyl, benzyl and C(O)(1-6C)alkyl, or two RO groups together form a (1-4C)alkylenedioxy group and Ac is acetyl, by reduction of the corresponding enamide of formula (II): Colchinol derivatives with high enantiomeric purity are obtained by hydrogenation in the presence of a transition metal catalyst, particularly a catalyst selected from a rhodium complex, a ruthenium complex or an iridium complex. Novel compounds of formula (II'): wherein each R, which may be the same or different, is selected from (1-6C)alkyl, benzyl and C(O)(1-6C)alkyl, or two RO groups together form a (1-4C)alkylenedioxy group, and P is hydrogen or a suitable hydroxy protecting group are also described.

Description

CHEMICAL PROCESSES FOR THE PREPARATION OF A COLCHINOL DERIVATIVE AND INTERMEDIATES

This invention relates to a chemical process and particularly to a chemical process for the preparation of vascular damaging agents, more particularly to a process for the preparation of colchinol derivatives such as N- acetyl colchinol (ZD6126 Phenol) and to intermediates used in the preparation of such compounds.

Colchinol derivatives such as N-acetylcolchinol are useful in the treatment of diseases involving angiogenesis.

The use of colchinol and derivatives thereof as a vascular damaging agents are described in International Patent Application publication number WO 99/02166. Other colchinol derivatives are described in, International Patent Application publication numbers WO 00/40529, WO 02/04434 and WO 02/08213.

A particular colchinol derivative which is described in International Patent Application publication number WO 99/02166 (Example 1 therein) is (5S)-5-(acetylamino)- 9,10,1 l-trimethoxy-6,7-dihydro-5H-dibenzo[a,c]cyclohepten-3-yl dihydrogen phosphate, also known as N-acetylcolchinol-O-phosphate and ZD6126, and which is referred to herein as ZD6126:

ZD6126 is a potent vascular targeting agent. Colchinol and derivatives thereof such as those described above are generally prepared by chemical modification of compounds whose basic carbon framework may be derived from the natural products such as colchicine:

For example, Patent Applications WO 99/02166 and WO 99/62506 describe, inter alia, compounds of the formula (A), which, may in general be made in a number of steps which include a rearrangement of colchicine to give a compound of the formula (A):

(A) wherein R₃>, R₄-, R₅-, R₆- and R₇- have any of the values defined in WO 99/02166 and WO 99/62506.

WO 99/02166 describes a synthesis of colchinol from colchicine which comprises (a) an acid hydrolysis using hydrochloric acid at a temperature of at or near 100°C, followed by (b) treatment of the resulting hydroxy ketone intermediate with alkaline hydrogen peroxide to give colchinol. This is illustrated in Scheme A.

Scheme A

Santavy, F., in Collect. Czech. Chem. Commun., 1949, 14 532-535 reports yields for this synthesis of 79% for step (a) and 25% for step (b) leading to an overall yield of 19%. This is obviously a less than ideal synthesis for use on a large scale.

Colchicine has been known as a starting material for chemical synthesis of colchinol derivatives for a number of years, see for example, V. Fernholz Justus, Liebigs Ann., 1950, 568, 63-72. The functional groups present in colchicine provide useful means of interconversion or introduction of functional groups, and one chiral centre is also present. Colchicine occurs naturally in the lily Gloriosa Superba, which is a native flower of

Northern India, and comprises approximately 1 to 2 wt% of the seed. The use of colchicine as a starting material on a commercial scale would result in the requirement for extensive growth of Gloriosa Superba, incur significant cost and potentially be vulnerable to unpredictable supply factors such as natural disasters. Therefore there is an on-going need for the provision of chemical processes to obtain colchinol and derivatives thereof, such as those of formula (A) without the use of colchicine to provide the basic carbon framework and chiral centre (at the ring carbon carrying R₄' in formula (A)). Advantageously such processes would be suitable for providing all compounds of the formula A including those wherein the nature of a group such as R₃ would not be (easily) accessible from colchicine as a starting material.

The availability of a robust chemical synthesis, suitable for the manufacture of colchinol, would provide a more reliable long-term supply of the compound and its associated derivatives. We have found that N-acetylcolchinol and derivatives thereof can be prepared in high yield as the racemate or in an enantiomerically enriched form, by reduction, for example hydrogenation of an enamide of the formula (II):

wherein R is defined hereinafter.

The enamide (II) is readily prepared from commercially available starting materials and can be produced on an industrial scale, making the enamide of formula (II) a particularly useful intermediate for the preparation of colchinol and derivatives thereof on an industrial scale without the need to use colchicine. It will be appreciated by those skilled in the art that for a process to be suitable for industrial application it should be amenable to being used on large scale, have minimal environmental impact (for example in terms of amount of raw materials required and/or the amount of waste produced), be safe (for example use materials of low toxicity that do not produce toxic waste), and be as low in cost as possible (for example by being high yielding). Enantioselective hydrogenations of dehydroamino acids of the general structure

R(H)C=CNCOR' (CO₂R"), which contain an enamide unit, are known and have been described for a number of catalyst systems; for example as described in R. Noyori, Asymmetric Catalysis in Organic Synthesis, Wiley, New York 1994; J.M. Brown, Comprehensive Asymmetric Catalysis Vol. 1 Chapter. 5 (ed. Jacobsen, Pfaltz and Yamamoto) Springerl9991, 2; and MJ. Burk, F. Bienewald, Transition Metal for Organic Synthesis, Chp.

1.1.2, "Unnatural α- Amino Acids via Asymmetric Hydro genations of Enamides", Ed. M.

Beller, C. BoIm, WILEY-VCH 1998; MJ. Bmk, Ace. Chem. Res., 2000, 33, 363.).

However, there are significantly fewer references to the hydrogenation of simpler enamides, although high enantioselectivity has been demonstrated with a range of catalysts including Rhodium catalysed hydrogenations described in inter alia: a) MJ. Burk, Y.M.

Wang, J.R. Lee, J. Am. Chem. Soc, 1996, 118, 5142. b) MJ. Burk, G. Casy, N.B. Johnson, J.

Org. Chem., 1998, 63, 6084. c) F.-Y. Zhang, C-C. Pai, A.S.C. Chan, J. Am. Chem. Soc,

1998, 120, 5808. d) G. Zhu, A.L. Casalnuovo, X. Zhang, J. Org. Chem., 1998, 63, 8100. e) G. Zhu, X. Zhang, J. Org. Chem., 1998, 63, 9590. f) Z. Zhang, G. Zhu, Q. Jiang, D. Xiao, X.

Zhang, J. Org. Chem., 1999, 64, 111 A. g) D. Xiao, Z. Zhang, X. Zhang, Org. Lett, 1999, 1,

1679. h) LD. Gridnev, N. Higashi, T. hnamoto, J. Am. Chem. Soc, 2000, 122, 10486. i) Y.-

Y. Yan, T.V. RajanBabu, Org. Lett., 2000, 2, 4137; and

Ruthenium catalysed hydrogenations described in inter alia: a) M. Kitamura, Y. Hsiao, M. Ohto, M. Tsukamoto, T. Ohta, H. Takaya, R. Noyori, J. Org. Chem., 1994, 59, 297. b)

D.M. Tschaen, L. Abramson, D.W. Cai, R. Desmond, U.H. Dolling, L. Frey, S. Karady, YJ.

Shi, T.R. Verhoeven, J. Org. Chem., 1995, 60, 4324).

The vast majority of the endocyclic enamide substrates described have five or six membered rings, and there are very few examples of asymmetric hydrogenations of enamide substrates with seven membered rings. One such reference is J.D. Armstrong, K.K. Eng, JL.

Keller, R.M. Purick, F.W. Hartner, W.B. Choi, D. Askin, R.P. Volante, Tetrahedron Lett.,

1994, 35, 3239. This paper describes, inter-alia, the hydrogenation of a capralactam precusor in 82 % enantiomeric excess.

We have surprisingly found that enamides of the formula (II) may be asymmetrically hydrogenated using certain catalysts to give an enantiomeric excess of the desired colchinol derivative. The present invention therefore also provides a robust means for preparing colchinol derivatives with high enantiomeric purity directly from an enamide of the formula

(II).

According to a first aspect of the present invention there is provided a process for the preparation of a colchinol derivative of the formula (I) :

which comprises the reduction of an enamide of the formula (II):

wherein each R, which may be the same or different, is selected from (l-6C)alkyl, benzyl and -C(0)(l-6C)alkyl, or two RO groups together form a (l-4C)alkylenedioxy group, and wherein any functional group in the compound of formula (II) is optionally protected, and whereafter any protecting group that is present is removed by conventional means. hi one embodiment, the R groups are all the same. hi another embodiment, each R, which may be the same or different, is selected from (l-4C)alkyl, benzyl and -C(O)(I -4C)alkyl. In a further embodiment, each R, which may be the same or different, is selected from (l-4C)alkyl and benzyl. In a further embodiment, each R, which may be the same or different is selected from (l-4C)alkyl. Particularly each R group is methyl.

The reduction is carried out by, for example hydrogenation of the enamide of the formula II. Hydrogenation may be by for example transfer hydrogenation or direct hydrogenation in the presence of a suitable catalyst.

When transfer hydrogenation is used a hydrogen donor in used in the presence of a suitable catalyst, such as a transition metal-ligand catalyst, particularly a rhodium, ruthenium or iridium metal-complex with a suitable ligand which may be a chiral ligand. Examples of hydrogen donors for transfer hydrogenation include, for example an alcohol or ammonium formate.

In one embodiment the hydrogenation is a catalytic hydrogenation wherein the enamide of formula II is reacted with hydrogen in the presence of a catalyst. A suitable catalyst includes, for example a transition metal catalyst, such as platinum, palladium, rhodium, ruthenium or iridium catalyst. The transition metal catalyst may for example, be used on a suitable substrate (for example a Pd/C catalyst), or the transition metal catalyst may be in the form of a complex of the transition metal with one or more ligands. A particular transition metal catalyst is selected from a rhodium, ruthenium and iridium catalyst and more particularly a catalyst selected from a rhodium complex, a ruthenium complex or an iridium complex. In a particular embodiment the catalyst is a rhodium complex or a ruthenium complex, because we have found that these catalysts provide a high yield of the colchinol or a derivative thereof of formula (I). hi an embodiment the reduction is effected by catalytic hydro genation of the enamide of formula II in the presence of a catalyst selected from a rhodium complex or a ruthenium complex, wherein the complex is formed with at least one ligand that contains one or more (for example one or two) phosphorus atoms.

When the transition metal catalyst is used as complex, a wide range of ligands may be used to form a complex with the transition metal.. Suitable ligands include, but are not limited to aryl, heteroaryl or heterocyclic containing moieties, which moieties may themselves be part of a complex, with for example another metal such as iron. Particular examples of ligands which may be used to form a complex with a transition metal such as rhodium, ruthenium or iridium include, but are not limited to, the ligands in Table 1.





In an embodiment the catalyst used in the process for the catalytic hydrogenation of the enamide of formula (II) is a rhodium, ruthenium or iridium complex, which complex comprises a primary bidentate ligand which contains two co-ordinating atoms, at least one of which is a phosphorus atom; and a secondary ligand or ligands comprising either (i) a second bidentate ligand or (ii) one or two mono-dentate ligands, which may be the same or different. For example the primary ligand of the catalyst contains one phosphorus co-ordinating atom and a second co-ordinating atom, for example a second co-ordinating atom selected from selected from phosphorus, oxygen and nitrogen, more particularly the second co-ordinating atom is phosphorus or nitrogen. Particular primary ligands include ligands which carry a chiral moiety, because, in general, the presence of a chiral moiety favours the asymmetric hydrogenation of the enamide of formula (II) and thereby provides an enantiomeric excess of one of the stereoisomers of the of the colchinol or a derivative thereof of formula (I). Examples of particular chiral ligands include, for example the chiral ligands shown in Table 1. The term "mono-dentate ligand" used herein refers to a ligand that forms one coordinate (dative) bond with the central metal ion in the complex. Similarly the term "bidentate ligand" refers to a ligand that forms two coordinate (dative) bonds with the central metal ion in the complex.

In a particular embodiment the catalyst used in the hydrogenation process is selected from a rhodium complex or a ruthenium complex of the formula (III), (IV), (V), (VI), (VII) or (VIII):

Is a chiral dentate in which P is phosphorous;

P-L³ is a chiral monodentate ligand in which P is phosphorous.

L is a neutral ligand; L is an anionic ligand; X is a coordinating atom; and Z^" is an anion. Suitably X is selected from phosphorus and nitrogen, particularly X is phosphorus.

Ligands L and L₂ are groups that are coordinated through π-bonds or through lone pair electrons.

Suitable neutral ligands represented by L are monodentate ligands derived from a neutral moiety, for example alkenes, alkynes, benzene or a phosphine; or two neutral ligands L together are incorporated into one bidentate species, for example a diene, such as 1,5- cyclooctadiene (hereinafter COD), or 2,5-norbornadiene.

Suitable anionic ligands represented by L₂ are ligands derived from anionic species, for example methallyl; acetato (O₂CCH₃), trifluoroacetato (O₂CCF₃) or halogeno (for example chloro). Examples of a suitable chiral bidentate ligand (P-X) include a bidentate ligand selected from one of the bidentate ligands shown in Table 1.

Examples of a suitable chiral monodentate ligand (L -P) include a monodentate e ligand selected from one of the monodentate ligands shown in Table 1 such as (R)- ETPhenylLANE, (R)-EtPhenylTANE, (S)-iPrPhenylTANE or (S)-MePhenylNANE or an alternative stereoisomer thereof.

Z^" may be any suitable anion, for example an anion selected from a halide (such as fluoride, chloride, bromide or iodide), a tetrahaloborate (such as BF₄ ^"), a phosphorushexahalide (such as PF₆ ^"), acetate (^"O₂CCH₃), trifluoroacetate (^"O₂CCF₃) and triflate (^"OSO₂CF₃). A particular catalyst which may be used in the process for the hydrogenation of an enamide of formula (II) includes, but is not limited to, a rhodium complex selected from Table 2, a ruthenium catalyst selected from Table 3 or an iridium complex selected from Table 4, or an alternative stereoisomer thereof:

Table 4. Iridium catalysts.

Foot notes to Table 2: * These catalysts were prepared by premixing the ligand shown with [Rh(COD)₂] BF₄, to provide the initial catalyst, used in the hydrogenation reaction.

Tables 2, 3 and 4 also illustrate the % conversion of ZD6126 enamide (R in formula (II) is methyl) to a colchinol of formula (I) in which R is methyl, by hydrogenating the ZD6126 enamide under a hydrogen atmosphere in the presence of the catalyst shown. In all cases the hydrogenation was performed in methanol with a molar ratio of enamide to catalyst of 100:1. The last column of Tables 2 to 4 marked "e.e" show the enantiomeric excess of the steroeisomers of formula (I) formed by the hydrogenation (a zero in this column indicating that a racemic mixture was formed). The abbreviations used in Tables 2 to 4 are defined in Table 1. Where reference is made to an alternative stereoisomer of a catalyst herein, for example one of the catalysts shown in Tables 2 to 4, it is meant an alternative stereochemical configuration of the specific catalyst listed, for example an alternative stereoisomer to (S)- iPrFerroTANE Ru(methallyl)₂ listed in Table 3 is (R)-iPrFerroTANE Ru(methallyl)₂.

Further particular catalysts which may be used in the process for the hydrogenation of an enamide of formula (II) include, those catalysts listed in Table 2, 3 or 4 which are indicated in the tables as providing at least a 50% conversion of ZD6126 enamide to a colchinol derivative of formula (I), more particularly those catalysts listed which are shown provide at least 60% more particularly at least 80% and still more particularly at least 90% conversion of ZD6126 enamide to a colchinol derivative of formula (I), and alternative stereoisomers of such catalysts. In another embodiment there is provided a process for the preparation of a colchinol derivative of the formula (I) in racemic form comprising the achiral hydrogenation an enamide of the formula (II) in the presence of a suitable catalyst. Suitable catalysts for the achiral hydrogenation of an enamide of formula (II) are those catalysts which provide a racemic mixture of the colchinol derivative of formula (I). Examples of such catalysts include [(DiPFc)Rh(COD)]BF₄, and other homogeneous metal complex systems such as Wilkinson's catalyst- (PPh₃)₃PRhCl, or a heterogeneous catalyst, such as a palladium or platinum catalyst which may be used together with a suitable support, for example Pd/C, PtC or PtO₂. As will be understood, the term "achiral hydrogenation" refers to catalytic hydrogenation of an enamide of formula (II) that results in a racemic mixture of the colchinol derivative of formula (I).

In a particular embodiment there is provided a process for the preparation of a colchinol or a derivative thereof of the formula (I) in racemic form comprising the catalytic hydrogenation an enamide of the formula (II) in the presence of a [(DiPFc)Rh(COD)]BF₄ catalyst, wherein DiPFc is as defined in Table 1 herein and COD is 1,5-cyclooctadiene

In another embodiment there is provided a process for the preparation of a colchinol derivative of the formula (I) in enantiomerically enriched form which comprises the hydrogenation an enamide of the formula (II) in the presence of a transition metal catalyst, wherein said catalyst is a catalyst selected from Table 2, 3 or 4 which is listed as providing an enatiomeric excess of more than 0, or an alternative stereoisomer of such a catalyst.

This embodiment provides an enantiomerically enriched form of the colchinol derivative of formula (I). The term "enantiomerically enriched" used herein refers to colchinol derivatives of the formula (I) that contain an enantiomeric excess of one of the enantiomers of the compound of formula (I); namely a mixture containing an excess of either the R- or S- isomer of the colchinol derivative of formula (I):

wherein each R is as hereinbefore defined.

The degree of enantiomeric enrichment produced by the hydrogenation process is quantified as the enantiomeric excess (ee) of the colchinol derivative of formula (I). The (ee) of an enantiomerically enriched mixture is defined as the percentage excess of a pure enantiomer (R or S) over the racemate (see for example: EX. Eliel, S.H. Wilen, L.N. Mander, Stereochemistiy of Organic Compounds, Wiley, 1994):

ee = [(R) -(S)]/[(R) +($)]xlOO% = %Maj or isomer - % Minor isomer

Accordingly, a racemic mixture (containing 50% of each enantiomer) has 0% enantiomeric excess whilst an optically pure product of the hydrogenation would have an enantiomeric excess of 100%.

In one embodiment the enantiomerically enriched form of the colchinol derivative of the formula (I) has an enantiomeric excess of the (S)-isomer of formula (I). In another embodiment the enantiomerically enriched form of the colchinol derivative of the formula (I) has an enantiomeric excess of the (R)-isomer of formula (I).

Suitably the enantiomeric excess is at least 20%. It is preferred however that the enantiomeric excess is at least 50%, particularly at least 70%, more particulalrly at least 98% and still more particularly at least 99.9%. The relative quantities of each enantiomer resulting from the process can be determined by routine methods in the art. For example the enantiomers may be separated chromatographically using a suitable chiral column; using chiral reagents in combination with

NMR spectroscopy; or by derivatisation with a chiral reagent followed by standard achiral separation or spectroscopic techniques. A particular example of a rhodium complex or ruthenium complex suitable as a catalyst for use in the preparation of a colchinol or a derivative thereof of the formula (I) in enantiomerically enriched form includes a catalyst selected from Table 5 or an alternative stereoisomer of such a catalyst.: Table 5

wherein the abbreviations for the ligands are as shown in Table 1 We have found that use of a catalyst shown in Table 5, or an alternative stereoisomer thereof, in a process for the hydrogenation of an enamide of formula (II) gives an efficient conversion of the enamide of formula (II) and provide a high enantiomeric excess of the colchinol or a derivative thereof of formula (I). Table 5 also shows the enantiomeric excess and % conversion of ZD6126 enamide (R in formula (II) is methyl) to N-acetyl colchinol (R is methyl in formula (I)), by hydro genating the ZD6126 enamide under a hydrogen atmosphere in the presence of the catalyst shown, hi all cases the hydrogenation was performed in methanol with a molar ratio of enamide to catalyst of 100: 1. In a particular embodiment the catalyst used in the process for the hydrogenation of an enamide of formula (II) is a ruthenium or rhodium complex, wherein one ligand of the complex is an (l-6C)alkyl-ferroTANE of the formula (VIII):

wherein each R², which may be the same or different is (l-6C)alkyl.

A particular value for R² is (l-4C)alkyl, for example, methyl, ethyl, propyl, ωo-propyl, butyl and tert-butyl. More particularly R² is a branched (3-4C)alkyl group such as zsO-propyl or tert-butyl We have found that (1 -6C)alkyl-ferroTA]SlE-ruthenium/rhodium complexes are highly enantioselective in the hydrogenation process and provide a colchinol or derivative thereof of the formula (I) with particularly high enantiomeric excess.

A particular (l-6C)alkyl-ferroTANE-ruthenium/rhodium complex for use as a catalyst in the hydrogenation of an enamide of formula (II) is selected from [(<S)-iPrFerroTANE RIi(COD)]BF₄, [(S)-tBuFerroTANE Rh(COD)]BF₄, (5)-EtFerroTANE Ru(O₂CCF₃)₂ and (S)- iPrFerroTANE Ru(methallyl)₂, or an alternative stereoisomer thereof, wherein the abbreviations for the ligands are as shown in Table 1.

In a further embodiment the catalyst for use in the hydrogenation of an enamide of formula (II) is selected from [(5)-tBuFerroTANE Rh(COD)]BF₄, [(5)-iPrFerroTANE Rh(methallyl)₂ and (^)-(S)-FcPPh₂CHCH₃PBUt₂ [Rh(COD) ₂] BF₄, or an alternative stereoisomer thereof, wherein the abbreviations for the ligands are as shown in Table 1.

In a further embodiment the catalyst for use in the hydrogenation of an enamide of formula (II) is [(5)-tBuFerroTANE Rh(COD)]BF₄ or [(5)-iPrFerroTANE Rh(methallyl)₂ or an alternative stereoisomer thereof, wherein the abbreviations for the ligands are as shown in Table 1. In embodiments the molar ratio of the enamide of formula (II) to catalyst is at least 10:1, for example at least 500:1 such as 1000:1 or greater. We have found that the use of a high molar ratio of enamide to catalyst minimises the amount of catalyst required, whist providing good conversion to the desired colchinol or derivative thereof in high enantiomeric excess.

We have surprisingly found that certain catalysts provide particularly high enantiomeric selectivity in larger scale manufacture (0.7g scale) when a high molar ratio of enamide to catalyst (typically from about 500:1 to about 1000:1) is used.

Accordingly, in another embodiment there is provided a process for the preparation of a colchinol or derivative thereof of the formula (I) as hereinbefore defined in an enantiomerically enriched form which comprises hydrogenation of an enamide of the formula (II) as hereinbefore defined in the presence of a catalyst selected from (<S)-iPrFerroTANE Ru(methallyl)₂ and [(5)-tBuFerroTANE Rh(COD)]BF₄, or an alternative stereoisomer thereof, and wherein the molar ratio of enamide to catalyst is from about 500:1 to about 1000:1 and wherein the abbreviations for the catalyst ligands are as defined in Table 1. The effect of a high molar ratio of enamide to catalyst is illustrated in Table 6. Table 6: Selected Catalysts at High Enamide to Catalyst ratios

For each catalysts shown in Tables 2 to 6 only one of the possible stereoisomers is of the ligands is shown. Those skilled in the art will understand that use of an alternative stereoisomer of the catalyst (for example (R)- instead of (S)-) will give the alternative enantiomer of the colchinol or derivative thereof of formula (I) to that shown in the tables, but with the same level of enantiomeric excess.

Those skilled in the art of asymmetric chemistry will understand that in the catalysts described herein (such as those in Tables 2 to 6) it is the 'primary' chiral ligand (generally the chiral ligand containing at least one phosphorus atom) which is primarily responsible for controlling the asymmetric induction of the hydrogenation reaction to thereby give an enantiomeric excess of the colchinol of formula (I). During the hydrogenation reaction other ligand(s) on the catalyst (for example cyclooctadiene) may be displaced by other groups as the catalytic cycle proceeds, for example by displacement in the presence of hydrogen, to produce an active form of the catalyst. The present invention encompasses both the specific catalysts mentioned herein and any active forms of said catalysts which may form in-situ as the hydrogenation reaction proceeds, for example as a result of ligand displacement in the presence of hydrogen and subsequent reaction with a solvent present, such as methanol to give the active form of the catalyst. The process according to this aspect of the invention is conveniently carried out in a suitable or diluent. Examples of suitable solvents include a (1-6C) alkyl alcohol such as methanol or ethanol, an ether such as tetrahydrofuran, a halogenated solvent such as methylene chloride or an aromatic hydrocarbon such as toluene or a mixture thereof. A particular solvent for use with a rhodium catalyst includes, for example, methanol, ethanol, tetrahydrofuran, toluene, methylene chloride or a mixture of methanol and toluene. A particular solvent for use with a ruthenium catalyst include for example methanol and mixture comprising methanol an one or more additional solvents, for example a mixture of methanol and toluene.

The hydrogenation reaction is carried out under a hydrogen atmosphere, which is optionally pressurised. For example the reaction may be performed at a pressure of from 1 to 5 bar of hydrogen.

The process is suitably carried out at ambient or at elevated temperature, for example a temperature from ambient to 100°C, more particularly from 20 to 8O°C.

A particularly preferred embodiment of the invention provides a process for the preparation of a colchinol derivative of the formula (IA) in an enantiomerically enriched form:

which comprises catalytic hydrogenation of an enamide of the formula (HA):

wherein the catalyst is selected from Table 2, 3 or 4 above which is listed as providing an enatiomeric excess of more than O, or an alternative stereoisomer of such a catalyst. A particular catalyst for use in this embodiment is a catalyst selected from [(S)- tBuFerroTANE Rh(COD)]BF₄, [(S)-iPrFerroTANE Rh(methallyl)₂ and the catalyst obtained by the reaction of (^)-(S)-FcPPh₂CHCH₃PBUt₂ and [RIi(COD) ₂] BF₄, or an alternative stereoisomer thereof, wherein the abbreviations for the ligands are as shown in Table 1.

The enantiomeric excess of the colchinol derivative of the formula (IA) in this embodiment is at least 70%, more preferably at least 80%, still more preferably at least 90% and especially at least 98%.

It is particularly preferred that this embodiment provides an enantiomeric excess of the (S)-isomer of the colchinol derivative of formula (IA) (of the formula (IA'); namely N- acetylcolchinol), because this can be used to prepare the vascular damaging agent ZD6126:

A particular catalyst that provides a high enantiomeric excess of the (S)- isomer of the compound of formula (IA) when used in the process for the catalytic hydrogenation of the enamide of the formula (II A) is a rhodium or ruthenium catalyst selected from Table 7: Table 7:

wherein the abbreviations for the ligands are as shown in Table 1

As in Table 2 the catalysts in Table 7 above marked with a * were prepared by premixing the ligands shown. Another particular catalyst that provides a high enantiomeric excess of the (S)- isomer of the compound of formula (IA) when used in the process for the catalytic hydrogenation of the enamide of the formula (HA) is (S)-iPrFerroTANE Ru(methallyl)₂ or [(i?)-tBuFerroTANE Rh(COD)]BF₄, wherein the abbreviations for the ligands are as shown in Table 1.

Suitable reaction conditions and molar ratios of enamide to catalyst for use in this embodiment are as hereinbefore defined.

If required, the colchinol derivative of formula (I) prepared using the process of the invention may be separated into substantially pure enantiomers using conventional methods, for example by: direct re-crystallisation of a mixture of colchinol derivatives of formula(I), that has an enantiomeric excess above that of the eutectic point for the compound; by for example simulated moving bed chromatography (SMB chromatograph); or by separation of diastereomeric salts or other derivatives, by re-crystallisation or chromatography. Preparation of Starting Materials The catalysts used in the process according to the invention are commercially available or can be prepared using known methods, for. example as described in Comprehensive Organometallic Chemistry, Pergamon 1982 and Comprehensive Organometallic Chemistry II, ed. Abel, Pergamon 1995.

Conveniently, the rhodium and ruthenium catalysts described herein which have a phosphorus containing ligand may be prepared by mixing a rhodium or ruthenium complex, for example [Rh(COD)₂]⁴BF₄ ^" with the required phosphorus containing ligand. A rhodium catalyst may be generated by mixing the ligand (i?)-(<S)-FcPPh₂CHCH₃PBut₂ with the rhodium complex [Rh(COD) ₂] BF₄ to give the initial catalyst for use in the reaction. As described hereinbefore, it is to be understood that the catalysts described herein may undergo further reaction in-situ in the reaction mixture, to generate the active form of the catalyst as part of the reaction cycle.

The catalyst starting materials and ligands described herein are commercially available or can be prepared using known methods or analogous methods thereto. For example, ferrocene ligands and catalysts are described in Berens et al ,Angewandte Chemie, International Edition (2000), 39(11), 1981-1984; Marinetti et al, European Journal of Inorganic Chemistry (2003), (14), 2583-2590; WO 2000/027855; and WO 99/24444;

PhenylLANE ligands and catalysts are described in Vedejs et al, Journal of Organic Chemistry (1996), 61(2), 430-1; and Burk et al, Tetrahedron: Asymmetry (1991), 2(7), 569-92; and PhenylTANE ligands and catalysts are described in WO 98/02445 and US5,936,109.

The enamide of formula (II) may be prepared form commercially available stating materials for example by a process comprising steps 1) to 5): 1) formation of a keto-aldehyde compound (IX)

wherein each R is as defined hereinbefore and wherein P is selected from (l-6C)alkyl, -SiL₃ (wherein each group L is independently selected from (l-6C)alkyl and aryl), benzyl and -C(O)(I -6C)alkyl; by transition metal mediated coupling of a compound of the formula (X) with a compound of the formula (XI) followed by conversion of any carbonyl group derivative into its parent carbonyl group;

wherein either a) R₁ is an imine; X₁ is halide; X₂ is halide; R₂ is an acetal or thioacetal; the transition metal is copper; P and R are as hereinbefore defined; or b) R₁ is an acetal; one OfX₁ and X₂ is halide and the other is -B(OH)₂ or B(OR₃)₂ (wherein each R₃ is independently (1 -4C)alkyl or wherein the two -OR₃ groups may be joined in a cycloalkyl ring, and wherein such a ring may contain methyl substituents on the carbons); R₂ is a ketone; the transition metal is palladium; P and R are as hereinbefore defined;

2) intramolecular cyclisation of the keto-aldehyde compound (IX) to form an enone (XI);

3) reduction and deprotection of the enone (XI) to form a cyclic ketone (XII);

4) formation of the oxime derivative (XIII) of the cyclic ketone (XII); and

5) reductive acylation to form the enamide (II).

As mentioned hereinbefore, the colchinol derivatives of formula (I) are useful as vascular damaging agents. Alternatively they can be further chemically modified to give other colchinol derivatives.

As mentioned hereinbefore, functional groups in the enamide of the formula (II) may be protected during the reaction. Protecting groups may in general be chosen from any of the groups described in the literature or known to the skilled chemist as appropriate for the protection of the group in question and may be introduced by conventional methods. Protecting groups may be removed by any convenient method as described in the literature or known to the skilled chemist as appropriate for the removal of the protecting group in question, such methods being chosen so as to effect removal of the protecting group with minimum disturbance of groups elsewhere in the molecule.

Specific examples of protecting groups are given below for the sake of convenience, in which "lower", as in, for example, lower alkyl, signifies that the group to which it is applied preferably has 1-4 carbon atoms. It will be understood that these examples are not exhaustive. Where specific examples of methods for the removal of protecting groups are given below these are similarly not exhaustive. The use of protecting groups and methods of deprotection not specifically mentioned are, of course, within the scope of the invention. For example the hydroxy group in the enamide of formula (II) may be protected during the reduction. Examples of hydroxy protecting groups include lower alkyl groups (for example tert-butyl), lower alkenyl groups (for example allyl); lower alkanoyl groups (for example acetyl); lower alkoxycarbonyl groups (for example tert-butoxycarbonyl); lower alkenyloxycarbonyl groups (for example allyloxycarbonyl); aryl-lower alkoxycarbonyl groups (for example benzyloxycarbonyl, 4-methoxybenzyloxycarbonyl, 2-nitrobenzyloxycarbonyl and 4-nitrobenzyloxycarbonyl); tri(lower alkyl)silyl (for example trimethylsilyl and tert-butyldimethylsilyl) and aryl-lower alkyl (for example benzyl) groups. Particular hydroxy protecting groups include, for example a group selected from (l-6C)alkyl, -SiL₃ (wherein each group L is independently selected from (l-όC)alkyl and aryl), benzyl, - CO(l-6C)alkyl and -CO₂(I -6C)alkyl. More particularly the hydroxy protecting group is selected from (l-όC)alkyl, -SiL₃ (wherein each group L is independently selected from (1- 6C)alkyl and aryl), benzyl and -CO₂(l-6C)alkyl. Still more particularly the hydroxy protecting group is selected from (l-4C)alkyl and -SiL₃ (wherein each group L is independently selected from (l-όC)alkyl and aryl). Suitable values for -SiL₃ include -SiMe₃, -SiEt₃, -SiPhMe₂, -Si¹Pr₃, -Si¹¹BuMe₂ and -Si¹BuPh₂. Conveniently, the hydroxyl protecting group is selected from benzyl, -SiMe₃, -SiPhMe₂, and -CO₂Me. Preferably, hydroxyl protecting group is benzyl.

Any protecting groups present may be removed at any convenient stage of the reaction. Methods appropriate for removal of, for example, hydroxy protecting groups are well known and include, for example, acid-, base-, metal- or enzymically-catalysed hydrolysis for groups such as 2-nitrobenzyloxycarbonyl, hydrogenation for groups such as benzyl and photolytically for groups such as 2-nitrobenzyloxycarbonyl.

The reader is referred to Advanced Organic Chemistry, 4th Edition, by J. March, published by John Wiley & Sons 1992, for general guidance on reaction conditions and reagents and to Protective Groups in Organic Synthesis, 2^nd Edition, by T. Green et ah, also published by John Wiley & Son, for general guidance on protecting groups. There follows particular and suitable values for certain substituents and groups referred to in this specification. These values may be used where appropriate with any of the definitions and embodiments disclosed hereinbefore, or hereinafter. For the avoidance of doubt each stated species represents a particular and independent aspect of this invention.

Suitable values for (l-4C)alkyl include methyl, ethyl, isopropyl, propyl, butyl, isobutyl and tertiarybutyl; suitable values for (l-6C)alkyl include (l-4C)alkyl, pentyl, cyclopentyl, hexyl and cyclohexyl; suitable values for -CO₂(I -4C)alkyl include -CO₂CH₃, - CO₂CH₂CH₃ and -CO₂tBu; suitable values for -CO₂(l-6C)alkyl include -CO₂(I -4C)alkyl and -C0₂ρentyl, suitable values for -C(O)(I -4C)alkyl include -C(O)CH₃, and - C(O)CH₂CH₃; suitable values for -C(O)(I -6C)alkyl include -C(O)(I -4C)alkyl and - C0₂ρentyl. The term 'aryl' means an aromatic carbocyclic ring, optionally substituted by 1, 2, or 3 substituents independently selected from (l-4C)alkyl, halo.

When two RO groups together form a (l-4C)alkylenedioxy group, the (1- 4C)alkylenedioxy group is, for example, methylenedioxy -(0CH₂O)- or ethylenedioxy - (OCH₂CH₂O)-. For example, when two adjacent RO groups form an ethylenedioxy group the enamide of formula (II) is of the formula (Ha) or (lib):

The enamide of formula (II) as hereinbefore defined which is used as the starting material in the process according to the invention is novel and provides a further independent aspect of the invention. According to a further aspect of the invention there is provided an enamide of the formula (H'):

wherein each R is as hereinbefore defined and P is hydrogen or a suitable hydroxy protecting group.

In an embodiment each R, which may be the same or different, is selected from (1- 4C)alkyl and benzyl. In a further embodiment, each R, which may be the same or different is selected from (l-4C)alkyl. Particularly each R group is methyl.

Suitable hydroxy protecting groups represented by P are as hereinbefore defined. For example P is hydrogen or a hydroxy protecting group selected from (l-6C)alkyl, -SiL₃ (wherein each group L is as defined hereinbefore), benzyl and -CO₂(I -6C)alkyl. Particularly P is hydrogen. A particular vascular damaging agent is ZD6126. This compound may be prepared by phosphorylation of N-acetylcolchinol to give ZD6126.

The invention will now be illustrated in the following non limiting examples, in which standard techniques known to the skilled chemist and techniques analogous to those described in these examples may be used where appropriate, and in which, unless otherwise stated: (i) evaporations were carried out by rotary evaporation in vacuo and work up procedures were carried out after removal of residual solids such as drying agents by filtration; (ii) all reactions were carried out under an inert atmosphere at ambient temperature, typically in the range 18-25°C, with solvents technical grade under anhydrous conditions, unless otherwise stated; (iii) the structures of the end products of the formula (I) were generally confirmed by nuclear (generally proton) magnetic resonance (NMR) and mass spectral techniques; magnetic resonance chemical shift values were measured in deuterated dimethyl sulphoxide (unless otherwise stated) on the delta scale (ppm downfield from tetramethylsilane); proton data is quoted unless otherwise stated; spectra were recorded on a on a Bruker DRX500 spectrometer; and peak multiplicities are shown as follows: s, singlet; d, doublet; dd, double doublet; t, triplet; tt, triple triplet; q, quartet; tq, triple quartet; m, multiplet; br, broad; LCMS were recorded on a Waters ZQ Mass Spec Detector, LC column was a SB C8 150mm x 3.0 mm 3.5um (Agilent Zorbax), detection with a HPl 100 with a Diode Array Detector; unless otherwise stated the mass ion quoted is [M + H]⁺; (iv) the following abbreviations may be used hereinbefore or hereinafter:- THF tetrahydrofuran; (v) the term ReI. VoIs (or VoIs) refers to the relative amount of solvent used in millilitres, relative to the amount of the main reaction substrate in grams

Reference Example 1:

JV-(3-Hydroxy-9,l 0,1 l-trimethoxy-7IZ-dibenzo [a,c] cyclohepten-S-yty-acetamide

Step l

Compound 2: 4'-Benzyloxy-2'-fU-(ethyIendioxy)ethyll-4.,5.ι6-trimethoxy-biphenyl-2- carbaldehyde

"Butyllithium (2.39M, 5.17 ml, 0.0123 mol) was added to a stirred solution of 2-(5- benzyloxy-2-bromophenyl)-2-methyl-[l,3]dioxolane (Intermediate 4, 4.12g, 0.0118 mol) in toluene (50 ml) and tetrahydrofuran (5 ml) at -78°C under dry nitrogen over 15 min. After 15 min, CuBr-P(OEt)₃ complex (5.25g, 0.0168 mol) in THF (5 ml) was added over 15 min. After a further 15 min, a solution of (2-bromo-3,4,5-trimethoxy-benzylidene)- cyclohexylamine (Intermediate 3, 4.Og, 0.0112 mol) in THF (15 ml) was added over 15 min. The mixture was then allowed to warm to room temperature over 16 h, then heated to 45°C for 48 h. Heating was then discontinued, aqueous acetic acid (10%, 50 ml) was added, and the mixture was stirred for 1 h. The organic layer was washed with aqueous acetic acid (10%, 50 ml), and brine (2 x 50 ml). The mixture was then filtered through a bed of celite and the resultant solution was evaporated under reduced pressure. The residue was dissolved in warm ethanol (20 ml) and the resultant solution was covered and left at room temperature overnight. Filtration, followed by drying in a vacuum oven at 4O°C, gave the title product (4.Og, 77% yield [90% strength by NMR] as a pale yellow crystalline solid.

¹H-NMR (400 MHz, CDCh) δ- 1.45 (3H, s), 3.48-3.54 (1H, m), 3.68 (3H, s), 3.73-3.80 (2H, m),

3.84-3.92 (1H, m), 3.95 (3H, s), 3.96 (3H, s), 5.13 (1H, s), 6.93 (1H, dd), 7.07 (1H, d), 7.32 (1H, s), 7.34-7.44 (3H, m), 7.37 (1H, d), 7.46-7.51 (2H, m), 9.47 (1H, s).

Step 2

Compound 6: 3-Benzyloxy-9,10.,ll-trimethoxy-dibenzofa,clcvcloheptan-5-one

A stirred mixture of 4'-benzyloxy-2'-[l,l-(ethylendioxy)ethyl]-4,5,6-trimethoxy-biphenyl-2- carbaldehyde (Compound 2, 4.0 g, 0.0078 mol) in ethanol (25 ml) was warmed to 65°C and treated with concentrated hydrochloric acid (~10M, 0.39 ml, 0.0039 mol). Water (18 ml) was then added and the clear solution was stirred for 2 h. Potassium carbonate (anhydrous) (1.59 g, 0.0116 mol) was then added and the temperature was raised to 9O°C. After 5 h the mixture was cooled in an ice bath for 30 min. then filtered under reduced pressure. The enone was collected as a yellow solid and washed with aqueous HCl (IM, 100 ml), then water (100 ml). It was then dried in a vacuum oven at 42°C overnight to give the title compound (3.16g, 91% yield).

¹H NMR (400 MHz, CDCh) δ: 3.44 (3H, s), 3.95 (3H, s), 4.00 (3H, s), 5.17 (2H, s ), 6.53 (1H, d), 6.78 (1H, s), 7.17 (1H, dd), 7.19 (1H, d), 7.30-7.50 (6H, m), 8.00 (1H, d).

Step 3

Compound 7: 3-Hydroxy-9,10,ll-trimethoxy-dibenzo[a,clcycloheptan-5-one

3-Benzyloxy-9,10,ll-trimethoxy-dibenzo[a,c]cycloheptan-5-one (Compound 6, 1.0 g, 0.0025 mol) and palladium hydroxide on carbon catalyst (0.1 g) were charged to a 200 ml hydrogenation vessel. THF (25 ml) and acetic acid (200 μL) were added and the flask was set-up on the hydrogenator. The vessel was purged with nitrogen (3 times), then with hydrogen (3 times), then left to react at 0.2 bar hydrogen pressure with stirring at lOOOrpm. After 19 h the mixture was filtered through celite and the solids were washed with dichloromethane (100 ml). The solvents were then evaporated from the filtrate and the residue crystallised from methanol (25 ml). The product was collected by filtration under reduced pressure and dried at 42°C in a vacuum oven, to provide, 0.62 g. 79% yield,

¹H NMR (400 MHz, CDCh) δ: 2.50-3.50 (4H, m), 3.50 (3H, s), 3.89 (3H, s), 3.90 (3H, s), 6.24 (1H, s), 6.60 (1H, s), 7.03 (1H, dd), 7.09 (1H, d), 7.47 (1H, d); m/z (Electrospray) 315 ([M + H]⁺, 100%);Found [M + H]⁺ 315.1242 Ci₈Hi₉O₅ requires 315.1232.

Step 4 Compound 8: 34Ivdroxy-94041-trimethoxy-dibenzora.,clcvcloheptan-5-one oxime

Pyridine (6.43 ml, 0.079 mol) was added in one portion to a stirred slurry of 3-hydroxy- 9,10,1 l-trimethoxy-dibenzo[a,c]cycloheptan-5-one (Compound 7, 10.70 g, 0.032 mol) and hydroxylamine hydrochloride (3.56 g, 0.054 mol) in absolute ethanol (100 ml) at room temperature. The resulting mixture was heated under reflux for 3 h. Water (250 ml) was then added at a constant rate over 10 min with continued heating. Heating was continued until the mixture had reached reflux and was then allowed to cool slowly to room temperature overnight. The mixture was cooled to 0-5°C for 2 h and filtered. The filter cake was washed with aqueous ethanol (1:3, EtOH, H₂0, 1 x 20 ml) and then dried in a vacuum oven (4O°C) overnight. The product was obtained as an off white solid (major isomer >90%) (10.72 g, 93%).

¹H-NMR (400 MHz, (UDMSOl (major isomer): δ 2.41-2.73 (3H, m), 3.03 (1H, ddd), 3.45 (3H, s), 3.73 (3H, s), 3.81 (3H, s), 6.75 (1H, s), 6.76 (1H, d), 6.83 (1H, dd), 7.22 (1H, d), 9.54 (1H, s), 10.95 (1H, s).

Accurate Mass : 330.1351 (C₁₈H₂₀NO₅ = 330.1341)

Step 5

Compound 9: iV-(3-Hydroxy-9,10.,ll-trimethoxy-7fl-dibenzofa,c1cvclohepten-5-vI)- acetamide

Acetic anhydride (10.74ml, 0.114 mol) was added in one portion to a stirred slurry of 3- hydroxy-9,10,l l-trimethoxy-dibenzo[a,c]cycloheptan-5-one oxime (Compound 8, 15.35g, 0.046 mol) in glacial acetic acid (150ml) at room temperature and the resulting mixture was stirred for 40 minutes. Iron powder (3.09g, 0.054 mol) was then added in one portion and stirring was continued for a further 4 hours. The solvents were removed in vacuo and the brown solid residue was partitioned between ethyl acetate (1000ml) and saturated aqueous sodium bicarbonate solution (300ml) (caution: effervescence!) and the mixture stirred vigorously for 10 min. The separated organic layer was washed with saturated aqueous sodium bicarbonate solution (300ml) and saturated brine (200ml) and dried (Na₂SO₄). The organic layer was concentrated by distillation under atmospheric pressure until 800ml of distillate had been collected. The resulting slurry was allowed to cool slowly to room temperature and then cooled to 0-5 °C for 3 hours. The product was isolated by filtration and the filter cake washed with cold ethyl acetate (2 x 15ml) and then dried in a vacuum oven (40°C). The enamide was obtained as a white solid (11.17g, 64%). ¹H-NMR (400 MHz, dfiPMSO): δ 1.91 (3H, s), 2.45 (1H, dd), 2.99 (1H, dd), 3.41 (3H, s), 3.73 (3H, s), 3.80 (3H, s), 6.37 (1H, dd), 6.72 (1H, s), 6.76 (1H, dd), 6.88 (1H, d), 7.43 (1H, d), 9.25 (1H, s), 9.52 (1H, br. s). Accurate Mass : 356.1517 (C₂₀H₂₂NO₅ = 356.1498) 2-(5-Benzyloxy-2-broinophenyl)-2-methyl-[l.,31dioxoIane

Ethylene glycol (23.8 g, 379.3 mmol) and para-toluenesulfonic acid monohydrate (2.44 g, 12.6 mmol) were added to a solution of 2-bromo-5-benzyloxy-acetophenone (40.0 g, 126.4 mmol) in toluene (500 ml). The solution was heated under reflux with stirring in a 3 -neck round-bottomed flask fitted with a Dean-Stark receiver for 3 hours. The reaction mixture was then cooled to room temperature. The mixture was transferred to a separating funnel and sodium carbonate solution (IM, 500 ml) was added. The mixture was agitated and two phases formed. The organic layer was separated and washed with water (2 x 500 ml). The organic layer was separated, dried (MgSO₄) and concentrated in a rotavapor to afford a white solid. This was dried in a vacuum oven at 40°C to give the desired product (42.34g). ¹H-NMR (200 MHz, CDClO: δ 1.80 (3 H, s), 3.65-4.10 (4 H, m), 5.05 (2 H, s) and 6.60-7.5 (8 H, m). [MH+] C₁₇H₁₈BrO₃ calcd = 349.0439, found 349.0468

Z-Bromo-S-benzyloxyacetophenone

N-Bromosuccinimide (69.8 g, 0.39 mol) was added to a solution of 3-benzyloxyacetophenone (80 g, 0.35 mol) in acetonitrile (300 ml) under nitrogen. The initial slurry was warmed to 6O°C with stirring, slowly becoming a homogeneous black solution. After 4 hours the acetonitrile was distilled off, the residue diluted with toluene (50 ml) and the solvent again distilled off. The mixture was then diluted with toluene (200 ml) and washed with IM sodium thiosulfate (2 x 300 ml). The organic layer was then separated, dried (MgSO₄) and concentrated under vacuum (40°C, ~5mm Hg). The residue was then dissolved in toluene (100 ml) and washed with IM potassium carbonate (2 x 100ml). The organic layer was then separated, dried (MgSO₄) and concentrated. This produced the crude product (112.6g, 76% strength by HPLC area %) from which 20 g was purified by flash column chromatography (hexane: ethyl acetate 95:5) and 20 g was recrystallised from heptane. This gave the pure product [(16.6 g, 80% yield, 92 % strength; by column chromatography) or (13.8g, 70% yield, 97% strength; by crystallisation)] as white crystals.

¹H-NMR (200 MHz, CDClO δ: 2.62 (3 H, s, CH₃), 5.06 (2 H, s, PhCH₂) and 6.86-7.52 (8 H, m, 5 x PhC-H & 3 x ArC-H).

3-Benzyloxyacetophenone

Potassium carbonate (151.2 g, 1094 mmol) was added to a solution of 3- hydroxyacetophenone (99.8g, 729.3 mmol) in DMF (400 ml). The solution was heated to 90°C with stirring. Benzyl chloride (96.9 g, 765.8 mmol) was then added from a syringe pump over 5 hours. After 6 hours, the reaction mixture was cooled to ambient temperature. The mixture was transferred to a round-bottomed flask and ~300 ml of DMF removed by evaporation under reduced pressure. Ethyl acetate (450 ml) was then added followed by water (600 ml). The organic layer was separated and washed with water (5 x 100ml). The organic layer was separated, dried (MgSO₄) and was concentrated to give the desired product (148.9 g)- ¹H-NMR (200 MHz, CDClQ δ: 2.59 (3 H, s), 5.11 (2 H, s) and 7.13-7.52 (9 H, m). [MH+] C₁₅H₁₅O₂ calcd = 227.1072, found 227.1087

Intermediate 2 2-(2-Bromo-3,4,5-trimethoxyphenyl)-fl,31dioxoIane

p-Toluenesulfonic acid (3.5 g, 0.018 mol) was added to a solution of 2-bromo-3,4,5- trimethoxybenzaldehyde (Intermediate 7, 50 g, 0.18 mol) and ethylene glycol (40 ml, 0.73 mol) in toluene (500 ml). The reaction mixture was heated to reflux for 6 hours then cooled and left at ambient temperature for 16 hours. The reaction was again heated to reflux for 5 hours, then potassium carbonate (5 g, 0.036 mol) followed by water (50 ml) were added. The mixture was separated and the organic layer washed with water (7 x 100 ml). The organic layer was t dried (MgSO₄) and concentrated under vacuum to give the product [98% yield, 96% strength (by HPLC area %)] as a tan coloured oil. ¹H-NMR (200 MHz, CDCM: δ 3.87 (6H, s), 3.88 (3H, s), 4.05-4.19 (4H, m), 6.04 (1H, s) and 6.99 (1H, s).

Intermediate s (2-Bromo-3,4,5-trimethoxybenzyIidene)-cvclohexylainine

A stirred solution of 2-bromo-3,4,5-trimethoxy benzaldehyde (Intermediate 7, 35 g, 0.127 mol) and cyclohexylamine, in toluene (175 ml) was heated at reflux under a Dean-Stark trap for 2 h. The solution was concentrated under vacuum and the residue was dissolved in isopropanol (70 ml) and cooled in an ice bath to induce crystallisation. Filtration, followed by drying in a vacuum oven at 4O°C, gave the product (39.7 g, 88% yield) as a white crystalline solid.

¹H NMR (400 MHz. CDClO δ : 1.19-1.45 (3H, m), 1.51-1.63 (2H, m), 1.64-1.79 (3H, m), 1.79- 1.88 (2H, m), 3.23-3.33 (1H, m), 3.89 (3H, s), 3.91 (3H, s), 3.92 (3H, s), 7.41 (1H, s), 8.63 (1H, s). Intermediate 7: 2-Bromo-3,4,5-trimethoxybenzaIdehyde

N-Bromosuccinimide (143 g, 0.80mol) was added to a solution of 3,4,5- trimethoxybenzaldehyde (150 g, 0.76 mol), in acetonitrile (750 ml). The reaction mixture was heated to 5O°C for 1 hour cooled and left at ambient temperature for 54 hours. On completion, sodium thiosulfate solution [24 g, 0.152 mol; in water (115 ml)] was added. The reaction mixture was then concentrated, diluted with dichloromethane (400 ml) and washed with water (2x 200 ml). The organic layer was then separated, dried (MgSO₄), concentrated and recrystallised from iso-propanol (50 ml). The title compound was produced as white crystals [96% yield, 100% strength (by HPLC area %)] . δ_H (200 MHz, CDCl₃) 3.89 (6 H, s), 4.96 (3 H, s), 7.27 (1 H, s) and 10.30 (1 H, s).

Copper (I) bromide - triethyl phosphite complex

Triethyl phosphite (183g, 1.1 mol) was added to a suspension of copper(I) bromide (164.5 g, 1.15 mol) in toluene (500 ml). The mixture was heated at 80°C for 3 h with stirring, then left to cool and settle. The clear solution was decanted from the solid residue and the solvent evaporated on a rotary evaporator at 60°C, to provide copper(I) bromide triethyl phosphite complex as a clear colourless oil, 336g (94% crude yield).

Example 1 Racemic N-Acetylcolchinol (R is methyl in formula (T))

A glass liner was charged with ZD6126 Enamide (enamide of the formula (II) wherein R is methyl) (0.1 g), [(DiPFc)Rh(COD)]BF₄ (1.9 mg) and a Teflon coated stir bar, the liner was placed in a pressure vessel which was assembled and purged with nitrogen. A hydrogen atmosphere was established by charging the reactor to 9 bar and venting three times. Methanol (3 ml) was added via syringe to the vessel. The vessel was purged with hydrogen a further six times then charged to 100 psi of hydrogen. The vessel was stirred at room temperature overnight and the pressure was released. The vessel was flushed with nitrogen prior to disassembly. Solvent was removed in vacuo to give a glassy solid. The ¹H NMR spectrum obtained in d -methanol was identical to an authentic sample of N- acetylcolchinol; ¹H NMR (400MHz DMSO-d_fi): δ 1.82-1.91 (1H, m, CH₂), 1-87 (3H, s, NHCOCH₅), 2.01-2.19 (2Η, m, CH₂), 2.43-2.53 (1Η, m, CH₂), 3.46 (3Η, s, OCH₃), 3.77 (3Η, s, OCH₃), 3.82 (3Η, s, OCH₃), 4.42-4.51 (1Η, m, CHNHCOCH₃), 6.68 (1H, dd, J 8, 2.5, 2'H), 6.74 (1H, s, 8'H), 6.76 (1H, d, J2.5, 4'H), 7.11 (1H, d, J8.3, l'H), 8.30 (1H, d, J8.5, NH), 9.35 (1Η, s, OH); Mass Spec: [M+Η⁺] 358.

Example 2

Preparation of N-Acetylcolchinol (R is methyl in the colchinol derivative of formula (I)) by Catalytic Hydrogenation of ZD6126 Enamide (formula II wherein R is methyl) in a Multicell Reactor

A glass liner was charged with ZD6126 Enamide (~0.53g, 0.15 mmol), the catalyst (-1.5 μmol) and a Teflon coated stir bar and purged with nitrogen. The liners were placed in a multi-well vessel. The vessel was flushed with nitrogen and a hydrogen atmosphere was established by charging the reactor to 9 bar and venting three times. Methanol (3 ml) was added via syringe to each well of the vessel. The vessel was purged with hydrogen a further six times then charged to 120 psi of hydrogen. The wells of the vessel were heated to the appropriate temperature and the wells were stirred via a stirrer hotplate. The reactions were allowed to stir overnight, the vessel was allowed to cool to room temperature and the pressure was released. The vessel was again flushed with nitrogen prior to disassembly. A further 8 ml of methanol was added to give a homogenous solution and a 1 ml sample of each reaction mixture (approximately 5 mg of product) was evaporated to dryness and ¹H NMR spectrum obtained in d⁴ methanol. The NMR samples were diluted to 5 ml total volume with methanol and submitted for HPLC analysis. The N-acetylcolchinol produced was identical to authentic material by spectroscopic (e.g. ¹H NMR, ¹³C NMR, IR, MS) and chromatographic (HPLC) methods of analysis.

The % conversion to colchinol and any enantiomeric excess is shown in Tables 2, 3 and 4 in the description above Example 3: N-acetylcolchinol in Enantiomeric Excess Prepared by Catalytic Hydrogenation of ZD6126 Enamide with Selected Catalysts at High Molar Ratio of Enamide to Catalyst

A glass liner was charged with ZD6126 Enamide (0.7g, 1.97mmol), (S)- iPrFerroTANE Ru(methallyl)₂ (1.4mg, 2 μmol) and a Teflon coated stir bar, the liner was placed in a pressure vessel which was assembled and purged with nitrogen. A hydrogen atmosphere was established by charging the reactor to 9 bar and venting three times. Methanol (20 ml) was added via syringe to the vessel. The vessel was purged with hydrogen a further six times then charged to 110 psi of hydrogen. The vessel was placed in an oil bath at 70 °C and stirred overnight, the vessel was allowed to cool to room temperature and the pressure was released. The vessel was flushed with nitrogen prior to disassembly and the solvent was then removed from the in vacuo to give a glassy solid. This was dissolved in ethyl acetate (50 ml), heptane (20 ml) was added and solvent was removed in vacuo. A dark residue from the catalyst precipitated and some of the product also precipitated. The bulk of the product was removed and further treatment with ethyl acetate and heptane was provided further material. The solvent was removed in vacuo (approximately 0.2 mrn/Hg, room temperature, 4 hours), yield 0.695 g, 99 % crude yield; 91.6 % enantiomeric excess of the (S) isomer. The N-acetylcolchinol produced was identical to authentic material by spectroscopic

(e.g. ¹H NMR, ¹³C NMR, IR₅ MS) and chromatographic (HPLC) methods of analysis.

Using an analogous procedure enantiomeric excesses of N-acetylcolchinol were prepared using the catalysts and enamide: catalyst molar ratios shown in Table 6 in the description.

Claims

1. A process for the preparation of a colchinol derivative of the formula (I) :

wherein each R, which may be the same or different, is selected from (l-6C)alkyl, benzyl and -C(O)(I -6C)alkyl, or two RO groups together form a (l-4C)alkylenedioxy group and Ac is acetyl, which comprises the reduction of an enamide of the formula (II):

wherein R is as defined for formula (I) and wherein any functional group in the compound of formula (II) is optionally protected; and thereafter, if necessary, removal of any protecting group.

2. A process according to claiml wherein the reduction is carried out by hydrogenation.

3. A process according to claim 2 wherein the hydrogenation is performed in the presence of a transition metal catalyst selected from a platinum, palladium, rhodium, ruthenium or iridium catalyst.

4. A process according to claim 3 wherein the catalyst is selected from a complex of rhodium, ruthenium or iridium with one or more ligands.

5. A process according to claim 4 wherein the at least one ligand is selected from:





6. A process according to any of claims 3 to 5 wherein the catalyst is selected from a rhodium complex or a ruthenium complex of the formula (III), (IV), (V), (VI), (VII) or (VIII):

is a chiral bidentate ligand in which P is phosophrous;

P-L³ is a chiral monodentate ligand in which P is phosphorus;

L is a neutral ligand; L² is an anionic ligand;

X is a coordinating atom selected from phosphorus and nitrogen; and Z^" is an anion.

7. A process according to any of claims 3 to 6 wherein the catalyst is selected from a rhodium complex of formula:

[DiPFc Rh(COD)]BF₄; [(R)-MeDuPHOS RJh(COD)]BF₄; [(S)-MeBPE Rh(COD)]BF₄; [(S)-EtFerroTANE Rh(COD)]BF₄; [(R)-MeDuPHOS Rh(COD)]BF₄; [(R)-MeDuPHOS Rh(COD)]BF₄; [(R)-EtDuPHOS Rh(COD)]BF₄; [(R)-IPrDuPHOS Rh(COD)]BF₄; [(S)-MeBPE Rh(COD)]OTf;

[(R)-EtBPE Rh(COD)]BF₄;

[(R)-iPrBPE Rh(COD)]BF₄;

[(R)-MeFerroLANE Rh(COD)]BF₄; [(R)-EtFerroLANE Rh(COD)]BF₄;

[(R)-iPrFerroLANE Rh(COD)]BF₄;

[(R)-MeFerroTANE Rh(COD)]BF₄;

[(S)-EtFerroTANE Rh(COD)]BF₄;

[(S)-EtFerroLANE Rh(COD)]BF₄; [(S)-nPrFerroT ANE Rh(COD)]BF₄;

[(S)-iPrFerroTANE Rh(COD)]BF₄;

[(S)-tBuFerroTANE Rh(COD)]BF₄;

[(R)-iPrPhanePHOS Rh(COD)]BF₄;

[(R)-PhanePHOS Rh(COD)]BF₄; [(S)- XylPhanePHOS Rh(COD)]BF₄;

[(S)-MeOXylPhanePHOS Rh(COD)]BF₄;

[(R)-(S)-JOSIPHOS Rh(COD)]BF₄;

[(R₅S)- FcPCy₂CH(CH₃)PPh₂ + [Rh(COD)]₂ BF₄;

(R)-(S)-FcPCy₂CHCH₃PCy₂ + [Rh(C0D)]₂ BF₄; (R)-(S)-FcPPh₂CHCH₃PBUt₂ + [Rh(C0D)]₂ BF₄;

[((S)-MePhenylNANE)₂ Rh(COD)]BF₄;

[((R)-EtPhenylTANE)₂ Rh(COD)]BF₄;

[((S)-MePhenylLANE)₂ Rh(COD)]BF₄;

{[(S)-iPrPhenylTANE]₂Rh(COD)}BF₄; [(R)-ClMeOBIPHEP Rh(COD)]BF₄;

[(S)-ToIBINAP Rh (COD)]BF₄;

[(R)-OxazolinePPh₂ Rh(COD)]BF₄;

[(S₅S)-DIOP Rh(COD)]BF₄;

[D-CARBOPHOS Rh(COD)]BF₄; [(S₅S)-CHIRAPHOS Rh(COD)]BF₄;

[(R₅R)-NORPHOS Rh(COD)]BF₄;

[(R)-QUINAP Rh(COD)]BF₄ ;

(S₅S)-BPPM + [Rh(COD)₂]BF₄;

[(R₅R)-DIPAMP Rh(COD)]BF₄; and [(R)-BINAM(PPh₂)I Rh(COD)] BF₄ or an alternative stereoisomer thereof, wherein the ligands are as defined in claim 5 and COD is 1,5-cyclooctadiene.

8. A process according to any of claims 3 to 6 wherein the catalyst is selected from a ruthenium catalyst selected from:

[(R)-MeDuPHOS Ru(O₂CCF₃)₂;

[(R)-MeDuPHOS Ru(C₆H₆)Cl]Cl; [(R)-MeDuPHOS Ru(C₆H₆)Cl]BF₄;

[(R)-MeDuPHOS Ru(C₆H₆)Cl]Cl;

(R)-EtDuPHOS RuBr₂;

(R)-EtDuPHOS Ru(O₂CCF₃)₂;

[(R)-iPrDuPHOS Ru(C₆H₆)Cl]Cl; (S)-MeBPE Ru(O₂CCFa)₂;

(R)-EtBPE Ru(methallyl)₂;

(R)-iPrBPE Ru(methallyl)₂;

(R)-iPrBPE RuBr₂;

(R)-MeFerroLANE Ru(O₂CCF₃)₂; (R)-EtFerroLANE Ru(O₂CCF₃)₂;

(S)-iPrFerroLANE Ru(O₂CCF₃)₂;

(S)-EtFerroTANE Ru(O₂CCF₃)₂;

(S)-iPrFerroTANE Ru(methallyl)₂;

(R)-(S)-JOSIPHOS Ru(O₂CCF₃)₂; (R)-(S)-FcPCy₂CHCH₃PCy₂ Ru(O₂CCF₃)₂;

(R)-(S)-FcPPh₂CHCH₃PtBu₂ Ru(O₂CCF₃)₂;

(R)-(S)-FcPCy₂CHCH₃PPh₂ Ru(O₂CCF₃)₂;

(S)-MeOBIPHEPRu(O₂CCF3)₂;

(-)-XylylClMeOBIPHEP Ru(O₂CCF₃)₂; [(R)-TolBINAP Ru(C₆H₆)Cl]Cl;

[(R)-ClMeOBIPHEP Ru(C₆H₆)Cl]Cl ;

[(R)-BINAP RuCl₂]₂NEt₃;

(S,S)-CHIRAPHOS RU(O₂CCF₃)₂;

(R₅R)-NORPHOS Ru(O₂CCF₃)₂; (S₅S)-BPPM Ru(O₂CCFs)₂;

(S₅S)DIOP Ru(O₂CCF₃)₂;

D-CARBOPHOS Ru(O₂CCF₃)₂;

(R₅R)-C₆H₄(PMePh)₂ Ru(methallyl)₂;

(R₅R)-BDPP Ru(O₂CCFs)₂; and (S)-iPrFerroTANE Ru(O₂CCFs)₂; or an alternative stereoisomer thereof, wherein the ligands are as defined in claim 5 and COD is 1,5-cyclooctadiene.

9. A process according to any of claims 3 to 6 wherein the catalyst is selected from an iridium catalyst selected from:

[(S)-EtDuPHOS Ir(COD)]PF₆; [(S)-EtFerroTANE Ir(COD)]BF₄; [(R)- OxazolinePPh₂ Ir(COD)]BF₄; [((R)-MePhenylTANΕ)₂ Ir(COD)]PF₆; [(R)-MeDuPHOS Ir(COD)]BF₄; [(R)-iPrDuPHOS Ir(COD)]BF₄ and [(R)-iPrBPE Ir(COD)]PF₆, or an alternative stereoisomer thereof, wherein the ligands are as defined in claim 5 and COD is 1,5-cyclooctadiene.

10. A process according to claims 3 to 6 wherein the catalyst is[(DiPFc)Rh(COD)]BF₄ , wherein DiPFc is as defined in claim 5 and COD is 1,5-cyclooctadiene .

11. A process according to any of claims 3 to 9 wherein the catalyst is selected from:

[(,S)-MeBPE Rh(COD)]BF₄;

[(i?)-iPrDuPHOS Rh(COD)]BF₄; [(63-MeBPE Rh(COD)]OTf;

[(S)-iPrFerroTANE Rh(COD)]BF₄;

[OS)-tBuFerroTANE Rh(COD)]BF₄;

[(S)- XylPhanePHOS Rh(COD)]BF₄;

[(R)-(S)- JOSIPHOS Rh(COD)]BF₄; (^)-(S)-FcPCy₂CHCH₃PCy₂ [Rh(COD) ₂] BF₄;

(^)-(S)-FcPPh₂CHCH₃PBUt₂ [Rh(COD)₂] BF₄;

[(OS)-MePhenylNANE)₂ Rh(COD)]BF₄;

P)-OxazolinePPh₂ Rh(COD)]BF₄;

[(5,,S)-CHIRAPHOS Rh(COD)]BF₄; (K)-MeDuPHOS Ru(O₂CCF₃)₂;

P)-MeDuPHOS Ru(C₆H₆)Cl]Cl;

P)-MeDuPHOS Ru(C₆H₆)Cl]BF₄;

[CR)-MeDuPHOS Ru(C₆H₆)Cl]Cl;

(5)-EtFerroTANE Ru(O₂CCF₃)₂; and (S)-iPrFerroTANE Ru(methallyl)₂; or an alternative stereoisomer thereof, wherein the ligands are as defined in claim 5 and COD is 1,5-cyclooctadiene.

12. A process according to claim 11 wherein the catalyst is selected from [OS)-iPrFerroTANE Rh(COD)]BF₄, [OS)-tBuFerroTANE Rh(COD)]BF₄, (<S)-EtFerroTANE Ru(O₂CCF₃)₂ and (<S)-iPrFerroTANE Ru(methallyl)₂, or an alternative stereoisomer thereof..

13. A process according to claim 12 wherein the catalyst is selected from (5)-iPrFerroTANE Ru(methallyl)₂ and [(5)-tBuFerroTANE Rh(COD)]BF₄, or an alternative stereoisomer thereof, and wherein the molar ratio of enamide to catalyst is from 500:1 to 1000:1

14. A process according to any of claims 3 to 13 wherein the hydrogenation is carried out in a solvent selected from a (1-6C) alkyl alcohol, an ether, a halogenated solvent, an aromatic hydrocarbon or a mixture thereof.

15. A process according to any of claims 3 to 14 wherein the hydrogenation is carried out at a temperature in the range from 20 to 8O°C.

16. A process according to any preceding claim for preparing a compound of formula (IA)

by catalytic hydrogenation of an enamide of formula (IIA)

17. A process according to claim 16 wherein the catalyst is selected from [(S)-tBuFerroTANE Rh(COD)]BF₄, [(SHPrFerroTANE Rh(methallyl)₂ and the catalyst obtained by the reaction of (^)-(S)-FcPPh₂CHCH₃PBUt₂ and [Rh(COD) ₂] BF_4, or an alternative stereoisomer thereof.

18. A process according to claim 16 wherein the catalyst is selected from

[(S)-MeBPE Rh(COD)]BF₄ ;

PHPrDuPHOS Rh(COD)]BF₄;

[(S)-MeBPE Rh(COD)]OTf;

[(SHPrFerroTANE Rh(COD)]BF₄; [(SHBuFerroT ANE Rh(COD)]BF₄;

[(S)- XylPhanePHOS Rh(COD)]BF₄;

[(R)-(S)- JOSIPHOS Rh(COD)]BF₄;

(^)-(S)-FcPCy₂CHCH₃PCy₂ [Rh(COD)₂] BF₄;

(^)-(S)-FcPPh₂CHCH₃PBUt₂ [Rh(COD) ₂] BF₄; [((S)-MePhenylNANE)₂ Rh(COD)]BF₄;

P)-OxazomiePPh₂ Rh(COD)]BF₄;

[(S,S)-CHIRAPHOS Rh(COD)]BF₄;

(^)-MeDuPHOS Ru(O₂CCF₃)₂;

P)-MeDuPHOS Ru(C₆H₆)Cl]Cl; P)-MeDuPHOS Ru(C₆H₆)Cl]BF₄;

P)-MeDuPHOS Ru(C₆H₆)Cl]Cl;

(S)-EtFerroTANE Ru(O₂CCF₃)₂;

(SHPrFerroTANE Ru(methallyl)₂; and or an alternative stereoisomer thereof, wherein the ligands are as defined in claim 5 and COD is 1,5-cyclooctadiene.

19. A process according to claim 16 wherein the catalyst is selected from (SHPrFerroTANE Ru(methallyl)₂ or p)-tBuFerroTANE Rh(COD)]BF₄, wherein the ligands are as defined in claim 5 and COD is 1,5-cyclooctadiene.

20. A compound of formula (H'):

(H') wherein each R, which may be the same or different, is selected from (l-6C)alkyl, benzyl and -C(O)(I -6C)alkyl, or two RO groups together form a (l-4C)alkylenedioxy group, and P is hydrogen or a suitable hydroxy protecting group.

21. A compound according to claim 20 wherein P is hydrogen or a group selected from(l- 6C)alkyl, -SiL₃ (wherein each group L is independently selected from (l-6C)alkyl, aryl, benzyl, -CO(l-6C)alkyl and -CO₂(I -6C)alkyl, benzyl and -CO₂(I -6C)alkyl.

22. A compound according to claim 20 or 21 wherein each R is methyl and P is hydrogen.