This invention relates to synthetic organic chemistry. Specifically, the invention relates to a process for preparing intermediates useful in the syntheses of valuable antifolate compounds.
Compounds known to have antifolate activity are well recognized as chemotherapeutic agents for the treatment of cancer. A series of N-(6-amino-(pyrrolo(2,3-d)pyrimidin-3-ylacyl)-glutamic acid derivatives of formula V: 
where
Y is CHxe2x95x90CH, O, or S;
R3 is hydrogen, chloro, or fluoro;
R4 is hydroxy, a carboxy protecting group, or NHCH*(C(D)R5)CH2CH2C(O)R5;
R5 is hydrogen or a carboxy protecting group;
R6 is hydrogen or an amino protecting group;
R7 is hydroxy or amino; and the configuration about the carbon atom designated * is S; and the pharmaceutical salts thereof were disclosed as antifolates or intermediates to antifolates in U.S. Pat. Nos. 4,684,653 and 4,882,334.
A key step in the synthesis of the compounds of formula V, disclosed in U.S. ""334 and ""653, is the hydrogenation of compounds of formula VI: 
where Z1 and Z2 are both hydrogen or taken together form a bond; R4xe2x80x2 is a carboxy protecting group or NHC*H(C(O)R5xe2x80x2)CH2CH2C(O)R5xe2x80x2;
R5xe2x80x2 is a carboxy protecting group; and
R6xe2x80x2 is an amino protecting group;
providing the isomeric mixture of compounds of formula V(a): 
The resulting compound of formula V(a) can optionally have its protecting groups removed to give an isomeric mixture of the compounds of formula V. U.S. ""334 and ""653 further taught that the individual diastereomers of formula V could be separated mechanically by chromatography or preferably the individual diastereomers could be separated by forming diastereomeric salts with chiral acids, such as camphorsulfonic acid, followed by selective crystallization of one of the diastereomers.
U.S. ""334 and ""653 taught that compounds of formula VI can be obtained by first coupling a compound of formula VII with a compound of formula VIII: 
where X is bromo or iodo; in the presence of a palladium/trisubstituted phosphine catalyst of the type described by Sakamoto in Synthesis, 1983, 312 et. seq.
The synthesis outlined above suffers in many respects. On an industrial scale, use of a noble metal catalyst is expensive, leads to purification and environmental issues, and can be erratic due to varying amounts of the precious metal that is in the correct oxidation state/complex form for catalysis. Furthermore, if the preferred crystallization separation procedure taught above is followed, after isolating a diastereomer by filtration, the filtrate will contain mixtures of the two diastereomers. This filtrate is often not amenable to further separation by crystallization, and thus separation efficiency suffers without resorting to an undesired chromatographic separation. In certain cases, e.g., where Y is S, R3 is hydrogen, R4 is NHC*H(C(O)R5)CH2CH2C(O)R5, and R7 is hydroxy, as much as 80% of the desired isomer (the one with greater antifolate activity) could be found in the filtrate/fractions.
An improvement over the prior art would not rely on precious metal catalysis to produce the compounds of formula VI and would increase the absolute yields of the desired diastereomer of formula VI from mixtures containing both diastereomers by crystallization.
The present invention relates to a compound of formula III: 
where:
Y is CHxe2x95x90CH, O, or S;
R is C1-C6 alkyl;
R1 and R2 are independently C1-C6 alkyl or taken together with the nitrogen to which they are attached form a heterocycle;
R3 is hydrogen, chloro, or fluoro;
R4 is hydroxy, a carboxy protecting group, or NHC*H(C(O)R5)CH2CH2C(O)R5 where the configuration about the carbon atom designated * is S; and
R5 is hydrogen or a carboxy protecting group; or a salt or solvate thereof.
The present invention also relates to a compound of formula IV: 
where:
R6 is hydrogen or an amino protecting group; and
R7 is hydroxy or amino; or a salt or solvate thereof.
Moreover, the present invention relates to a process for preparing compounds of formula IV: 
which includes reacting a compound of formula III(a): 
where:
R4xe2x80x2 is a carboxy protecting group or NHC*H(C(O)R5xe2x80x2)CH2CH2C(O)R5xe2x80x2 where the configuration about the carbon atom designated * is S; and
R5xe2x80x2 is a carboxy protecting group;
with 2,4-diamino-6-hydroxypyrimidine in the presence of a suitable acid and solvent.
Furthermore, the present invention also relates to a process for preparing a compound of formula IV, or a salt or solvate thereof, which includes reacting a compound of formula V(b): 
or a salt or solvate thereof, with an oxidizing reagent in the presence of a suitable solvent.
In the general formulae of the present document, the general chemical terms have their usual meanings. For example, the term xe2x80x9cC1-C4 alkylxe2x80x9d refers to methyl, ethyl, propyl, isopropyl, cyclopropyl, n-butyl, s-butyl, t-butyl, and cyclobutyl. The term xe2x80x9cC1-C6 alkylxe2x80x9d encompasses those listed for C1-C4 alkyl in addition to aliphatic, straight, branched, or cyclic, monovalent moieties having five or six carbon atoms and includes, but is not limited to, pentyl, cyclopentyl, hexyl, cyclohexyl, 2-methylpentyl, and the like. The term xe2x80x9cC1-C4 alkoxyxe2x80x9d refers to a C1-C4 alkyl group attached through an oxygen atom.
The term xe2x80x9chaloxe2x80x9d or xe2x80x9chalidexe2x80x9d refers to chloro, bromo, or iodo.
The term xe2x80x9cheterocyclexe2x80x9d refers to a 5 or 6 membered saturated, partially unsaturated, or aromatic heterocyclic ring which contains a nitrogen atom and may optionally contain an additional heteroatom selected from N, S, or O.
The term xe2x80x9ccarboxy protecting groupxe2x80x9d refers to a substituent of a carbonyl that is commonly employed to block or protect the carboxy functionality while reactions are carried out on other functional groups on the compound.
This substituent, when taken with the carbonyl to which it is attached, may form an ester, e.g., C1-C6 alkyl, substituted C1-C6 alkyl, C2-C6 alkenyl, substituted C2-C6 alkenyl, benzyl, substituted benzyl, benzhydryl, substituted benzhydryl, trityl, substituted trityl, and trialkylsilyl ester. The exact species of carboxy protecting group is not critical so long as the derivatized carboxy group is stable to the conditions of subsequent reaction(s) and can be removed at the appropriate point without disrupting the remainder of the molecule. When R4 contains a carboxy protecting group, the protecting group is preferably C1-C4 alkoxy or benzyloxy. The most preferred protecting groups are methoxy, ethoxy, and benzyloxy. A carboxy protecting group xe2x80x9cremovable by catalytic hydrogenationxe2x80x9d includes, for example, benzyl protecting groups. Other examples of these groups are described in T. W. Greene, xe2x80x9cProtective Groups in Organic Synthesis,xe2x80x9d John Wiley and Sons, New York, N.Y., (2nd ed., 1991), (hereafter referred to as Greene) chapter 5.
The term xe2x80x9cC2-C6 alkenylxe2x80x9d refers to a mono-unsaturated, monovalent, hydrocarbon moiety containing from 2 to 6 carbon atoms which may be in a branched or straight chain configuration. The term is exemplified by moieties such as, but not limited to, ethylenyl, propylenyl, allyl, butylenyl, and pentylenyl.
The terms xe2x80x9csubstituted C1-C6 alkylxe2x80x9d and xe2x80x9csubstituted C2-C6 alkenylxe2x80x9d refer to a C1-C6 alkyl and C2-C6 alkenyl group respectively substituted from 1 to 3 times independently with a halo, phenyl, tri(C1-C4 alkyl)silyl, or a substituted phenylsulfonyl group.
The terms xe2x80x9csubstituted benzylxe2x80x9d, xe2x80x9csubstituted benzhydrylxe2x80x9d, and xe2x80x9csubstituted tritylxe2x80x9d refers to a benzyl, benzhydryl, and trityl group, respectively, substituted from 1 to 5 times independently with a nitro, C1-C4 alkoxy, C1-C6 alkyl, or a hydroxy(C1-C6 alkyl) group. These substitutions will only occur in a sterically feasible manner such that the moiety is chemically stable.
The term xe2x80x9ctrialkylsilylxe2x80x9d refers to a monovalent silyl group substituted 3 times independently with a C1-C6 alkyl group.
The term xe2x80x9csubstituted phenylsulfonylxe2x80x9d refers to a henylsulfonyl group where the phenyl moiety is para ubstituted with a C1-C6 alkyl, nitro, or a halo group.
The term xe2x80x9camino protecting groupxe2x80x9d as used in the specification refers to a substituent of the amino group commonly employed to block or protect the amino functionality while reacting other functional groups on the compound. The amino protecting group, when taken with the nitrogen to which it is attached, can form a cyclic imide, e.g., phthalimido and tetrachlorophthalimido; a carbamate, e.g., methyl, ethyl, and 9-fluoroenylmethylcarbamate; or an amide, e.g., N-formyl and N-acetylamide. The exact genus and species of amino protecting group employed is not critical so long as the derivatized amino group is stable to the condition of subsequent reaction(s) on other positions of the intermediate molecule and can be selectively removed at the appropriate point without disrupting the remainder of the molecule including any other amino protecting group(s). In general, amino protecting groups removable by acid hydrolysis, i.e., those that are acid labile, are preferred. Thus, a preferred amino protecting groups is 2,2-dimethyl-1-oxopropyl. Further examples of groups and methods referred to by the above terms are described in Greene at chapter 7.
The term xe2x80x9cpharmaceutical saltxe2x80x9d and xe2x80x9csaltxe2x80x9d as used herein, refers to salts prepared by reaction of the compounds of the present invention with a mineral or organic acid (e.g., hydrochloric, hydrobromic, hydroiodic, or p-toluenesulfonic acid) or an inorganic base (e.g., sodium, potassium, lithium, and magnesium hydroxide, carbonate, or bicarbonate). Such salts are known as acid addition and base addition salts. For further exemplification of these salts, see, e.g., Berge, S. M, Bighley, L. D., and Monkhouse, D. C., J. Pharm. Sci., 66, 1, 1977.
The term xe2x80x9csolvatexe2x80x9d represents an aggregate that comprises one or more molecules of a solute, such as a formula III or IV compound, with one or more molecules of solvent.
The term xe2x80x9csuitable solventxe2x80x9d refers to any solvent, or mixture of solvents, inert to the ongoing reaction that sufficiently solubilizes the reactants to afford a medium within which to effect the desired reaction.
The term xe2x80x9csuitable acidxe2x80x9d refers to an acid whose Ka is low enough to effect the desired reaction without significantly effecting any undesired reactions.
The term xe2x80x9coxidizing reagentxe2x80x9d refers to a reagent whose oxidation potential is high enough to effect the desired reaction without significantly effecting any undesired reactions. Suitable oxidants include metals such as nickel, palladium, platinum, and the like; metals on solid supports such as palladium or platinum on carbon, and the like; metal complexes such as mercury(II), manganese dioxide, or coppor(II) acetate, and benzoquinone based oxidants such as 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) and tetrachloro-1,4-benzoquinone (chloranil), and the like.
The term xe2x80x9cthermodynamic basexe2x80x9d refers to a base which provides a reversible deprotonation of an acidic substrate or is a proton trap for those protons that may be produced as byproducts of a given reaction, and is reactive enough to effect the desired reaction without significantly effecting any undesired reactions. Examples of thermodynamic bases include, but are not limited to, acetates, acetate dihydrates, carbonates, bicarbonates, C1-C4 alkoxides, and hydroxides (e.g., lithium, sodium, or potassium acetate, acetate dihydrate, carbonate, bicarbonate, C1-C4 alkxoxide, or hydroxide), tri(C1-C4 alkyl)amines, or aromatic nitrogen containing heterocycles (e.g., imidazole and pyridine).
The compounds of formula III may be prepared from compounds of formula I and II as illustrated in Scheme 1 below where Lg is chloro, bromo, iodo, OSO2Me, OSO2-phenyl, or OSO2-p-toluenyl and R, R1, R2, R3, R4, R4xe2x80x2, and Y are as defined above. 
Compounds of formula I, may be added to compounds of formula II dissolved or suspended in a suitable solvent, in the presence of a thermodyanamic base, to form the compounds of formula III(a). A preferred and convenient solvent is dichloromethane. A preferred and convenient base is triethylamine. A single equivalent of base and compound of formula I, relative to the compound of formula II, is preferably employed but slight excesses on the order of 0.01 to 0.1 equivalents are tolerable. The reaction may be performed between xe2x88x9278xc2x0 C. and ambient temperature but is preferably performed between xe2x88x9225xc2x0 C. and xe2x88x9220xc2x0 C. The reaction is typically complete in from 30 minutes to 18 hours but when performed at the preferred temperature, it is complete in from 1 to 3 hours. A preferred halide in compounds of formula I is chloride. R is preferably C1-C4 alkyl, especially methyl or ethyl. R1 and R2 are preferably C1-C4 alkyl but it is especially preferred when both are either methyl or ethyl. It is preferred that R4xe2x80x2 is a carboxy protecting group where that protecting group is C1-C4 alkoxy, especially methoxy or ethoxy, or one capable of being removed by catalytic hydrogenation, e.g., benzyloxy (as in Scheme 3 below). Throughout this specification, R3 is preferably hydrogen and Y is preferably CHxe2x95x90CH or S.
Although the resulting compound of formula III(a) may have its carboxy protecting group removed as taught in Greene, for the purposes of conducting the overall process of Schemes 1-3, the carboxy protecting is preferably left intact when proceeding to the reaction(s) of Scheme 2.
Compounds of formula IV may be prepared from compounds of formula III(a) by the novel process illustrated in Scheme 2 below where R, R1, R2, R3, R4, R4xe2x80x2, R6, R7, and Y are as defined above. 
A tautomeric mixture of 2,4-diamino-6-hydroxypyrimidine or 2,4-diaminopyrimidin-6-one (hereafter referred to as 2,4-diamino-6-hydroxypyrimidine) may be added to a compound of formula III(a), dissolved or suspended in a suitable solvent, in the presence of a suitable acid, to provide the compounds of formula IV(a). A convenenient and preferred solvent is an approximately 1:1 (v:v) mixture of acetonitrile and water. The ratio of acetonitrile to water is not critical but it is preferred that the ratio is amenable to forming a solution when the reactants are all initially combined. A convenient and preferred acid is acetic acid. The acid is typically employed in molar excess. For example, about 2 to about 4 equivalents, relative to the compound of formula III(a), is generally employed while 3 equivalents are typically preferred. The number of equivalents of 2,4-diamino-6-hydroxypyrimidine employed relative to the compound of formula III(a) is not critical but about 1 to about 2 equivalents are preferred. An even more preferred amount is about 1 to about 1.5 with about 1 to about 1.1 equivalents most preferred. The reaction may be performed at temperatures ranging from room temperature to the reflux temperature of the mixture but is preferably performed at the reflux temperature of the mixture. Furthermore, the reaction may take from 12 to about 48 hours depending on the temperature of the reaction. When the reaction is performed at the reflux temperature of the mixture, it is typically substantially complete in about 18 hours. R is preferably C1-C4 alkyl, especially methyl or ethyl. R1 and R2 are preferably C1-C4 alkyl but it is especially preferred when both are either methyl or ethyl. R3 is preferably hydrogen. As stated previously, it is preferred that R4xe2x80x2 is a carboxy protecting group where that protecting group is a C1-C4 alkoxy group, especially methoxy or ethoxy, or one capable of being removed by catalytic hydrogenation (as in Scheme 3).
The compounds of formula IV where R7 is an amino group may be prepared from the compounds of formula IV(a) as taught in the previously incorporated by reference U.S. Pat. No. 4,882,334 but it is preferred that R7 is hydroxy.
The compounds of formula IV where R6 is an amino protecting group may be prepared from compounds of formula IV(a) as taught in Greene or as discussed in Preparation 8 below. Furthermore, it is necessary that an amino protecting group, preferably one removable by acid hydrolysis as in Scheme 5 below, e.g., 2,2-dimethyl-1-oxopropyl be present at R6 or that the amino group be protonated before proceeding to the hydrogenation described in Scheme 3 below. Moreover, although the compounds of formula IV(a) may have their carboxy protecting groups removed as taught in Greene, for the purposes of conducting the overall process of Schemes 2-3, it is preferred that the carboxy protecting group is left intact when proceeding to the reaction of Scheme 3.
An isomeric mixture of compounds of formula V(b) may be prepared from compounds of formula IV(b) as illustrated in Scheme 3 below where R3, R4, R6xe2x80x2, R7, and Y are as defined above. 
Compounds of formula IV(b), prepared as described in Schemes 1 and 2, may be hydrogenated substantially as described in U.S. Pat. Nos. 4,684,653 and 4,882,334, the teachings of each are hereby incorporated by reference. For facilitation of cross reference, the compounds of formula IV(b) in the present invention correspond to the compounds of formula III in U.S. ""653 and the compounds of formula II in U.S. ""334. It is preferred that the amino protecting group at R6xe2x80x2 is not removed as taught in Greene but left intact when continuing to the separation procedures discussed in Schemes 4 and 5 below.
If the process of Scheme 3 is performed with the compounds of formula IV(b) with the preferred group at R4, i.e., a carboxy protecting group, and that carboxy protecting group is removable by catalytic hydrogenation, then that protecting group will be removed by the hydrogenation conditions of the reaction of Scheme 3. That removal, forming the compounds of formula V(b) where R4 is hydroxy, facilitates the installation of the R4 group found in the antifolate final products, i.e., the chiral glutamic acid, discussed below.
Compounds of formula V which possess antifolate activity are those where R4 is NHC*H(C(O)R5)CH2CH2C(O)R5) and R6 is hydrogen (hereafter referred to as xe2x80x9cfinal productsxe2x80x9d), and thus, those compounds are preferred. Although the glutamate side chain can be installed at any point in the overall process of this invention, when the processes of Schemes 1, 2, 3 are performed in sequence, with the preferred groups noted above, a preffered time to install the glutamate residue is after performing the hydrogenation described in Scheme 3. This is accomplished by coupling a compound of formula V or V(b) where R4 is hydroxy with a carboxy protected glutamic acid derivative of the formula H2NC*H(C(O)R5xe2x80x2)CH2CH2C(O)R5xe2x80x2, in the manner generally described in PCT application WO 86/05181, utilizing conventional condensation techniques for forming peptide bonds. These techniques include activation of the carboxy group through formation of a mixed anhydride or acid chloride, treatment with dicyclohexylcarbodiimide, or use of diphenylchlorophosponate. For further instruction on general methods of forming this amide bond, see, e.g., Bodanszky, M., Principles of Peptide Synthesis, 2nd Ed., Springer-Verlag, Berlin, Heidelberg, 1993. It is preferred that the glutamate side chain is present and that the R5 groups found in that side chain are both carboxy protecting groups, e.g., C1-C6 alkoxy, when performing the processes of Schemes 4 and 5. All discussions and structures pertaining to Schemes 4 and 5 below relate to the situation where the preferred substituents at R4 are present but those substituents are not required for the processes of Scheme 4 and 5 to be operable.
Of the final product compounds of formula V, the compounds of formula V(c)(R), shown below, are preferred due to enhanced antifolate activity relative to the compounds of formula V(c)(S). These individual diastereomeric final products, prepared as described above or in the previously incorporated by reference U.S. Pat. Nos. 4,684,653 and 4,882,334, may be separated as taught in those patents, i.e., by chromatography or preferably recrystallization. For example, an appropriately selected chiral acid may be employed to form a mixture of diastereomeric salts more amenable to selective recrystallization of one diastereomer as illustrated in Scheme 4 below where R3, R5xe2x80x2, R6, R7, and Y are as defined above. 
In order to carry out the separation of Scheme 4, it is necessary that R6 in compounds of formula V(c) is hydrogen. If the process of Scheme 4 is performed with the preferred group at R6, i.e., a protecting group removable by acid hydrolysis such as 2,2-dimetyl-1-oxopropyl, then that protecting group will be removed by the addition of the chiral acid and a separate step to remove it will not be necessary. Thus, compounds of formula V(c) where R6 is hydrogen do not necessarily have to be prepared in a separate step before proceeding to the resolution process of Scheme 4. The elimination of the requirement for this extra step is why acid labile amino protecting groups are preferred.
The first step in Scheme 4 is the addition of a chiral acid to a mixture of compounds of formula V(c) dissolved or suspended in a suitable solvent. This addition performs two functions: the chiral acid removes the amino protecting group at R6 and forms a diastereomeric acid addition salt of the compound of formula V(d). When Y is CHxe2x95x90CH, a preferred acid for this purpose is (1S)-(+)-camphorsulfonic acid. When Y is O or S, a preferred acid is (1R)-(xe2x88x92)-camphorsulfonic acid. A preferred solvent for the removal of the protecting group and formation of the salt is a lower alcohol preferably ethanol.
Once the salt is formed, the separation or recrystallization of Step 2 is performed by suspending the compounds of formula V(d) in a suitable solvent, heating the mixture until a solution is formed, and then allowing the solution to cool in order to precipitate the desired isomer. The important parameters in a chiral resolution in general, and when specifically resolving the compounds of formula V(d), are the solvent system, stir rate, and temperature. Preferred solvent systems are mixtures of a lower alcohol, preferably ethanol, and water. The ratio of ethanol to water by volume can be from about 0.33 to about 3 to 1, but a 1:1 mixture is preferred. The ratio of solvent to solute should be about 10 to about 20 to 1 but the preferred ratio is about 15 to 1. The rate of stirring during crystallization can have a marked effect on the resolution. It is preferred that once the salts are formed and dissolved by heating in the crystallization solvent, that the samples are not stirred while cooling. Temperature may also have an impact on resolution. Continued cooling below ambient temperature can increase the recovery of product but at the expense of separation efficiency. It is preferred to allow the crystallization to occur at a temperature between about 20xc2x0 C. and 34xc2x0 C. with ambient temperature (about 22xc2x0 C.) being most preferred.
In order to avoid hydrolysis of the esters on the glutamate residue by the aqueous acidic conditions of the resolution, a buffer such as sodium acetate is preferably employed. An amount of sodium acetate approximately equal to the excess of the acid is preferably added after solvolysis of the amino protecting group is complete.
The filtrate produced in Scheme 4 will contain a mixture of diastereomeric salts of formula V(d). This mixture is enhanced with the diastereomer of formula V(d)(S), i.e., the acid addition salt of V(d)(S), that didn""t crystallize. This enhanced mixture is not usually amenable to further separation by crystallization. Thus, a large majority of the desired isomer was heretofore unrecoverable by further crystallization. Scheme 5 below, where R3, R4xe2x80x2, R6, R7, and Y are as defined above, illustrates another novel method of preparing compounds of formula IV which facilitates the further separation of this mixture by crystallization. 
If the process of Scheme 5 is to be performed using the contents of the filtrate from Scheme 4 as a source of starting materials, it is preferred that the free base compounds of formula V(c) are first extracted from that mixture. This is easily accomplished by diluting the mixture with a water immiscible organic solvent and treating the mixture with a weak base dissolved in water such as a solution of sodium bicarbonate in water. Dichloromethane and aqueous sodium bicarbonate are preferred reagents for this purpose. For example, treatment of the filtrate with dichloromethane (about 0.33 mL/g filtrate) and about 2 equivalents of 1M aqueous sodium bicarbonate for about 30 minutes at room temperature will afford two clear, readily-separable phases. The organic phase is separated and preferably dried with a common drying agent or agents before proceeding. Sequential washes with brine and 1M aqueous sodium bicarbonate is a preferred drying procedure.
Once the extraction procedure is performed, an amino protecting group must be reinstalled at R6 or that amino group must be protonated before performing the process illustrated in Scheme 5. Reprotection is preferred and may be accomplished as taught in Greene cited above or as discussed in Preparation 9 below. It is preferred that the amino protecting group be removable by acid hydrolysis, e.g., a 2,2-dimethyl-1-oxopropyl protecting group. The resulting compounds of formula V(e) are then separated as follows.
Single diastereomers or mixtures of any ratio of compounds of formula V(e) may be dissolved or suspended in a suitable solvent and an oxidizing reagent added to provide the compounds of formula IV(b). Choice of solvent, reaction temperatures, and times will depend generally on the oxidizing reagent employed.
DDQ is a preferred oxidizing agent. When DDQ or chloroanil is employed as the oxidizing agent, hydrocarbons such as pentane, hexane, toluene, and the like; lower alcohols such as methanol, ethanol, isopropanol, and the like; or chlorinated hydrocarbons such as chloroform, dichloromethane, and the like; are suitable. Chlorinated hydrocarbons, especially dichloromethane, are preferred. When the oxidation is performed under the preferred conditions on the preferred compounds of formula V(e), chromatography to purify the resulting compounds of formula IV(b) is generally not necessary. See, e.g., Example 6 below.
The reaction is typically allowed to proceed at temperatures between 0xc2x0 C. and 200xc2x0 C. for from about 30 minutes to about 24 hours. The reaction is preferably performed at temperatures between 15xc2x0 C. to 80xc2x0 C. Even more preferred is when the reaction is performed between 20xc2x0 C. to 40xc2x0 C., and most preferred is when the reaction is performed at room temperature for from 20 minutes to 1 hour.
The amount of oxidizing reagent will vary depending on which oxidant is employed but will generally range from about 0.1 equivalents to about 5 equivalents relative to the compound of formula V(e). When DDQ is employed, about 1.1 to about 3 equivalents are preferred. Even more preferred is from 1.8 to about 2.2 equivalents while 1.9 to about 2.1 equivalents is most preferred.
The carboxy and/or amino protecting groups in compounds of formula IV(b) are preferably not removed as taught in Greene. Instead, a preferred course of action is to reduce the compounds of formula IV(b) back to a 50:50 diastereomeric mixture of compounds of formula V(e) in order to perform the chiral acid separation taught in Scheme 4.
The hydrogenation may be performed by dissolving or suspending a compound of formula IV(b) in a suitable solvent, in the presence of a hydrogenation catalyst, and exposing the mixture to an atmosphere of hydrogen. A convenient and preferred solvent is about a 4:1 mixture by volume of tetrahydrofuran and ethanol. A convenient and preferred hydrogenation catalyst is 5% palladium on carbon. The catalyst is typically employed, relative by weight to compounds of formula IV(b), in a range of from about 10% to about 200%. Preferably, the range is from about 20% to about 75%, with about 25% being preferred. It is typically preferred to create an atmosphere of hydrogen where the pressure of hydrogen is equal to or greater than that of ambient pressure. A typical pressure range is from about ambient to about 100 psi of hydrogen. More preferred is an atmosphere of hydrogen between 40 psi and about 60 psi with 50 psi most preferred. The reaction may be performed at temperatures ranging from ambient to about the reflux temperature of the mixture. At 50 psi of hydrogen, the preferred reaction temperature is about 100xc2x0 C., with the reaction typically substantially complete in less than 4 hours.
Once a 1:1 mixture of compounds of formula V(e) is formed as described in Scheme 5, it is further amenable to separation as discussed in Scheme 4 above. This cycle may be repeated as many times as the practitioner wishes in order to maximize the yield of the diastereomer of formula V(d)(R).
2,4-Diamino-6-hydroxypyrimidine, protected glutamic acids of the formula H2NC*H(C(O)R5xe2x80x2)CH2CH2C(O)R5xe2x80x2 and compounds of formula I and II are known in the art, and, to the extent not commercially available are readily synthesized by standard procedures commonly employed in the art. For example, see Preparations 1-6 below.
The optimal time for performing the reactions of Schemes 1-5 can be determined by monitoring the progress of the reaction by conventional chromatographic techniques. Choice of solvent is generally not critical so long as the solvent employed is inert to the ongoing reaction and sufficiently solubilizes the reactants to afford a medium within which to effect the desired reaction. Unless otherwise indicated, all of the reactions described herein are preferably conducted under an inert atmosphere. A preferred inert atmosphere is nitrogen.