NOVEL SYNTHESIS OF CHOLESTEROL

Abstract

The invention relates to a synthesis of cholesterol; a ring opening step of the compound of formula (I) and subsequent activation and reduction step yielding cholesterol. The inventions relates also to intermediates achieved during said synthesis.

Claims

1. A synthesis method of cholesterol comprising: a) a ring opening step, wherein the compound of formula (I) ##STR00025## is reacted in a Clemmensen reaction or a variant thereof, yielding compound of formula (II); ##STR00026## b) an activation step with SOCl.sub.2, PBr.sub.3 R.sup.4SO.sub.2X, yielding a compound of formula (III), preferably (IIIa); ##STR00027## c) a reduction step, wherein compound (III) is reacted with a reducing agent, yielding cholesterol (IV) ##STR00028## wherein R.sup.1 is selected from unsubstituted or substituted alkyl, amino acid, cyclic alkyl, particularly a C.sub.2-C.sub.6 cyclic alkyl, or alkyl-R.sup.2, heterocycle, an aromatic or heteroaromatic group, particularly R.sup.1 is selected from unsubstituted or substituted alkyl, amino acid, cyclic alkyl, particularly a C.sub.2-C.sub.6 cyclic alkyl, or alkyl-R.sup.2, more particularly from unsubstituted or substituted alkyl, amino acid or alkyl-R.sup.2, R.sup.2 is selected from H, OH, CN, NH.sub.2, NHR.sup.3 or NR.sup.3.sub.2, R.sup.3 is an unsubstituted or substituted C.sub.1-C.sub.6 alkyl, R.sup.4 is a substituted or unsubstituted alkyl, cyclic alkyl or aromatic group, X is a leaving group or OSO.sub.2R.sup.4 Z is Cl, Br or OSO.sub.2R.sup.4, preferably OSO.sub.2R.sup.4.

2. The method according to claim 1, wherein compound (I) is provided by a reaction of diosgenin (V) ##STR00029## with compound of a formula R.sup.1COY, wherein R.sup.1 has the same meaning as defined above and Y is a leaving group, wherein in particular the leaving group is selected from halogen, particularly Cl.

3. The method according to claim 1, wherein the amino acid of R.sup.1 is selected from ?-, ?- or ?-amino acid, particularly ?-amino acid, more particularly alanine, valine, leucine, isoleucine.

4. The method according to claim 1, wherein the alkyl of R.sup.1 is a unsubstituted or substituted C.sub.2-C.sub.10 alkyl, more particularly a unsubstituted or substituted C.sub.2-C.sub.6 alkyl, even more particularly C(CH.sub.3).sub.3, wherein in particular the alkyl are branched.

5. The method according to claim 1, wherein the alkyl-R.sup.2 of R.sup.1 is defined by a C.sub.1-C.sub.6 alkyl for the alkyl and R.sup.2 is selected from H, OH, NHR.sup.3 or NR.sup.3.sub.2, particularly from OH, NHR.sup.3 or NR.sup.3.sub.2, more particularly from NHR.sup.3 or NR.sup.3.sub.2, even more particularly R.sup.2 is NR.sup.3.sub.2, wherein R.sup.3 is an unsubstituted or substituted C.sub.1-C.sub.6 alkyl, particularly a C.sub.1-C.sub.3 alkyl, more particularly a C.sub.1 alkyl.

6. The method according to claim 1, wherein the aromatic group of R.sup.1 is phenyl or a substituted phenyl, particularly a substituted phenyl, wherein the substituent is selected from NHR.sup.3 or NR.sup.3.sub.2, particularly from NR.sup.3.sub.2, wherein R.sup.3 is an unsubstituted or substituted C.sub.1-C.sub.6 alkyl, particularly a C.sub.1-C.sub.3 alkyl, more particularly a C.sub.1 alkyl.

7. The method according to claim 1, wherein R.sup.1 is (R.sup.5)(R.sup.6)(R.sup.7)C(C?O)O, with each of R.sup.5, R.sup.6 or R.sup.7 being selected independently from H, a C.sub.1-C.sub.6 alkyl, particularly a C.sub.1-C.sub.3 alkyl, OH, NHR.sup.3 or NR.sup.3.sub.2, particularly from a C.sub.1-C.sub.6 alkyl, particularly a C.sub.1-C.sub.3 alkyl, OH, or NHR.sup.3, NR.sup.3.sub.2, more particularly from a C.sub.1-C.sub.6 alkyl, particularly a C.sub.1-C.sub.3alkyl, OH or NR.sup.3.sub.2, even more particularly from a C.sub.1-C.sub.6 alkyl, particularly a C.sub.1-C.sub.3 alkyl or NR.sup.3.sub.2 wherein particularly in case of one of R.sup.5, R.sup.6 or R.sup.7 is selected from OH, NHR.sup.3 or NR.sup.3.sub.2 the other two are selected from H, a C.sub.1-C.sub.6 alkyl, particularly a C.sub.1-C.sub.3 alkyl, wherein R.sup.3 is an unsubstituted or substituted C.sub.1-C.sub.6 alkyl, particularly a C.sub.1-C.sub.3 alkyl, more particularly a C.sub.1 alkyl.

8. The method according to claim 1, wherein the ring opening step is performed in the presence of a base metal, in particular Zn, and a strong acid, wherein in particular the strong acid is selected from HCl, HBr, H.sub.2SO.sub.4, HNO.sub.3, more particularly the strong acid is HCl.

9. The method according to claim 1, wherein ring opening step is performed in an organic, polar or nonpolar solvent, particularly toluene or an alcohol, particularly an C.sub.1-C.sub.6 alcohol, or a mixture thereof.

10. The method according to claim 9, wherein the solvent is a mixture of nonpolar and polar solvents, particularly toluene/alcohol, more particularly toluene/C.sub.2-C.sub.4 alcohol, even more particularly toluene/ethanol or toluene/propanol, wherein the ratio between the nonpolar and polar solvents, particularly toluene/alcohol, is in between 3:1 to 1:10, more particularly between 1:1 to 1:3.

11. The method according to claim 1, wherein R.sup.4 is selected from F, a perfluorated C.sub.1-C.sub.6 alkyl, C.sub.1-C.sub.6 alkyl, or C.sub.1-C.sub.6alkyl phenyl, particularly F, a perfluorated C.sub.1-C.sub.3 alkyl, C.sub.1-C.sub.3 alkyl, or C.sub.1-C.sub.3alkyl phenyl, more particularly F, methyl, trifluoromethyl, methyl phenyl.

12. The method according to claim 1, wherein the leaving group of X is selected from halogen, particularly Cl.

13. The method according to claim 1, wherein reducing agent is metal hydride or organometal hydride, particularly an aluminum hydride or a boron hydride or mixtures or complexes containing aluminum hydride or boron hydride, more particularly the reducing agent is LiAlH.sub.4, Red-Al, DIBAL or LiBHEt.sub.3.

14. The method according to claim 2, wherein the leaving group Y is selected from OH, dinitrogen, dialkyl ether, halogen, alkylcarboxylates, perfluoroalkylsulfonates, alkylsulfonates, nitrate, phosphate, amide, particularly halogen, even more particularly chloride.

15. A compound of general formula (I), formula (II) or formula (III), particularly (IIIa) in particular formula (II) or formula (III), particularly (IIIa), ##STR00030## wherein R.sup.1 has the same definition as above with the exception that R.sup.1 is not an unsubstituted alkyl ##STR00031## wherein R.sup.1 has the same definition as above, ##STR00032## wherein R.sup.1, R.sup.4 and Z have the same definition as above.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0048] The first aspect of the invention in the synthesis method of cholesterol comprising: [0049] a ring opening step, wherein the compound of formula (I)

##STR00009## [0050] is reacted in a Clemmensen reaction or a variant thereof, yielding compound of formula (II).

[0051] This reaction allows for efficient opening of both tetrahydrofuran and tetrahydropyran rings, yielding long, saturated, branched side chain, that is critical for the subsequent synthesis of cholesterol.

[0052] Subsequently the compound of formula (II)

##STR00010##

[0053] is reacted in an activation step with an activating agent, selected from SOCl.sub.2, PBr.sub.3 or R.sup.4SO.sub.2X, yielding a compound of formula (III), preferably (IIIa).

##STR00011##

[0054] The activation allows for a subsequent reduction of the two hydroxyl groups position.

[0055] A subsequent reduction step with a reducing agent yielding cholesterol (IV).

##STR00012##

[0056] The reduction step allows the reduction of the activated hydroxyl positions as well as the deprotection of the protected R.sup.1COO position in one synthesis step.

[0057] The entire sequence of reactions enables synthesis of cholesterol from plant-based chemical compound with a high yield and minimal waste production. In the above-described sequence [0058] R.sup.1 is selected from unsubstituted or substituted alkyl, amino acid, cyclic alkyl, particularly a C.sub.2-C.sub.6 cyclic alkyl, or alkyl-R.sup.2, heterocycle, an aromatic or heteroaromatic group, particularly R.sup.1 is selected from unsubstituted or substituted alkyl, amino acid, cyclic alkyl, particularly a C.sub.2-C.sub.6 cyclic alkyl, or alkyl-R.sup.2, more particularly from unsubstituted or substituted alkyl, amino acid or alkyl-R.sup.2, [0059] R.sup.2 is selected from H, OH, CN, NH.sub.2, NHR.sup.3 or NR.sup.3.sub.2, [0060] R.sup.3 is an unsubstituted or substituted C.sub.1-C.sub.6 alkyl, [0061] R.sup.4 is a substituted or unsubstituted alkyl, cyclic alkyl or aromatic group, [0062] X is a leaving group or OSO.sub.2R.sup.4 [0063] Z is Cl, Br or OSO.sub.2R.sup.4, preferably OSO.sub.2R.sup.4.

[0064] The method disclosed in the current invention enables efficient conversion of a plant-based diosgenin to cholesterol. Addition of an organic moiety to the 3-hydroxyl group protects it from reacting with any mild reactants in any subsequent steps, but it is deprotected in the last reduction step. This protection enables opening of tetrahydropyran and tetrahydrofuran rings in a previously unattainable way, leading to formation of a steroid nucleus with a free hydroxyl group and a long, saturated and branched side chain capped with a free hydroxyl group at the pentane ring. The free hydroxyl groups are then activated, that enables removal of these groups while retaining the original hydroxyl group. This solution allows easy and efficient conversion of diosgenin into cholesterol.

[0065] In an embodiment, the compound I is achieved by a reaction of diosgenin V

##STR00013##

[0066] with a compound of formula R.sup.1COY, wherein R.sup.1 is defined as above and Y is a leaving group.

[0067] The protecting group R.sup.1CO allows for a protection during the ring opening reaction and a deprotection during the reduction step of the activated hydroxyl groups of the ring opening sequence. The protecting group is chosen in such a way that it allows for a good protection while retaining a suitable solubility during the reaction process of the ring opening step.

[0068] In certain embodiments R.sup.1 is an amino acid.

[0069] In some embodiments R.sup.1 is ?-, ?- or ?-amino acid, particularly an ?-amino acid, more particularly a hydrophobic amino acid with short a hydrocarbon chain.

[0070] In some embodiments R.sup.1 is alanine, valine, leucine or isoleucine.

[0071] In certain embodiment R.sup.1 is a branched or linear, unsubstituted or substituted C.sub.2-C.sub.10 alkyl. In certain embodiments R.sup.1 is a branched or linear, unsubstituted or substituted C.sub.2-C.sub.6 alkyl. In some embodiments R.sup.1 is a branched alkyl.

[0072] In certain embodiment R.sup.1 is a branched or linear C.sub.2-C.sub.10 alkyl. In certain embodiments R.sup.1 is a branched or linear C.sub.2-C.sub.6 alkyl.

[0073] In some embodiments R.sup.1 is C(CH.sub.3).sub.3.

[0074] In certain embodiments R.sup.1 is in a form of alkyl-R.sup.2, wherein alkyl is C.sub.1-C.sub.6 alkyl and R.sup.2 is selected from H, OH, NHR.sup.3 or N(R.sup.3).sub.2, wherein R.sup.3 is an unsubstituted or substituted C.sub.1-C.sub.6 alkyl, particularly an unsubstituted alkyl, particularly a C.sub.1-C.sub.3 alkyl, more particularly a C.sub.1 alkyl.

[0075] In certain embodiments R.sup.1 is in a form of alkyl-R.sup.2, wherein alkyl is C.sub.1-C.sub.6 alkyl and R.sup.2 is selected from OH, NHR.sup.3 or N(R.sup.3).sub.2, wherein R.sup.3 is an unsubstituted or substituted C.sub.1-C.sub.6 alkyl, particularly an unsubstituted alkyl, particularly a C.sub.1-C.sub.3 alkyl, more particularly a C.sub.1 alkyl.

[0076] In certain embodiments R.sup.1 is in a form of alkyl-R.sup.2, wherein alkyl is C.sub.1-C.sub.6 alkyl and R.sup.2 is selected from NHR.sup.3 or N(R.sup.3).sub.2, wherein R.sup.3 is an unsubstituted or substituted C.sub.1-C.sub.6 alkyl, particularly an unsubstituted alkyl, particularly a C.sub.1-C.sub.3 alkyl, more particularly a C.sub.1 alkyl.

[0077] In certain embodiments R.sup.1 is in a form of alkyl-R.sup.2, wherein alkyl is C.sub.1-C.sub.6 alkyl and R.sup.2 is N(R.sup.3).sub.2, wherein R.sup.3 is an unsubstituted or substituted C.sub.1-C.sub.6 alkyl, particularly an unsubstituted alkyl, particularly a C.sub.1-C.sub.3 alkyl, more particularly a C.sub.1 alkyl.

[0078] In certain embodiments R.sup.1 is in a form of aromatic group, wherein the aromatic group is phenyl or a substituted phenyl.

[0079] In certain embodiments R.sup.1 is in a form of aromatic group, wherein the aromatic group is a substituted phenyl, wherein the substituent is NHR.sup.3 or NR.sup.3.sub.2, wherein R.sup.3 is an unsubstituted or substituted C.sub.1-C.sub.6 alkyl, particularly an unsubstituted alkyl, particularly a C.sub.1-C.sub.3 alkyl, more particularly a C.sub.1 alkyl.

[0080] In certain embodiments R.sup.1 is in a form of aromatic group, wherein the aromatic group is a substituted phenyl, wherein the substituent is NR.sup.3.sub.2, wherein R.sup.3 is an unsubstituted or substituted C.sub.1-C.sub.6 alkyl, particularly an unsubstituted alkyl, particularly a C.sub.1-C.sub.3 alkyl, more particularly a C.sub.1 alkyl.

[0081] In certain embodiments R.sup.1 is in a form of a moiety of a formula (R.sup.5)(R.sup.6)(R.sup.7)C(C?O)O, with each of R.sup.5, R.sup.6 or R.sup.7 being selected independently from H, a C.sub.1-C.sub.6 alkyl, particularly a C.sub.1-C.sub.3 alkyl, OH, NHR.sup.3 or NR.sup.3.sub.2, wherein R.sup.3 is an unsubstituted or substituted C.sub.1-C.sub.6 alkyl, particularly an unsubstituted alkyl, particularly a C.sub.1-C.sub.3 alkyl, more particularly a C.sub.1 alkyl, wherein in particularly in case of one of R.sup.5, R.sup.6 or R.sup.7 is OH, NHR.sup.3 or NR.sup.3.sub.2 the other two are selected from H or C.sub.1-C.sub.6 alkyl, particularly a C.sub.1-C.sub.3 alkyl.

[0082] In certain embodiments R.sup.1 is in a form of a moiety of a formula (R.sup.5)(R.sup.6)(R.sup.7)C(C?O)O, with each of R.sup.5, R.sup.6 or R.sup.7 being selected independently from H, a C.sub.1-C.sub.6 alkyl, particularly a C.sub.1-C.sub.3 alkyl, OH, NHR.sup.3 or NR.sup.3.sub.2, wherein R.sup.3 is an unsubstituted or substituted C.sub.1-C.sub.6 alkyl, particularly an unsubstituted alkyl, particularly a C.sub.1-C.sub.3 alkyl, more particularly a C.sub.1 alkyl, wherein at least one of R.sup.5, R.sup.6 or R.sup.7 is OH, NHR.sup.3 or NR.sup.3.sub.2 and the other two are selected from H or C.sub.1-C.sub.6 alkyl, particularly a C.sub.1-C.sub.3 alkyl.

[0083] In certain embodiments R.sup.1 is in a form of a moiety of a formula (R.sup.5)(R.sup.6)(R.sup.7)C(C?O)O, with each of R.sup.5, R.sup.6 or R.sup.7 being selected independently from a C.sub.1-C.sub.6 alkyl, particularly a C.sub.1-C.sub.3 alkyl, OH, or NHR.sup.3, NR.sup.3.sub.2, wherein R.sup.3 is an unsubstituted or substituted C.sub.1-C.sub.6 alkyl, particularly an unsubstituted alkyl, particularly a C.sub.1-C.sub.3 alkyl, more particularly a C.sub.1 alkyl, wherein in particularly in case of one of R.sup.5, R.sup.6 or R.sup.7 is OH, NHR.sup.3 or NR.sup.3.sub.2 the other two are selected from H or C.sub.1-C.sub.6 alkyl, particularly a C.sub.1-C.sub.3 alkyl.

[0084] In certain embodiments R.sup.1 is in a form of a moiety of a formula (R.sup.5)(R.sup.6)(R.sup.7)C(C?O)O, with each of R.sup.5, R.sup.6 or R.sup.7 being selected independently from a C.sub.1-C.sub.6 alkyl, particularly a C.sub.1-C.sub.3 alkyl, OH or NR.sup.3.sub.2, wherein R.sup.3 is an unsubstituted or substituted C.sub.1-C.sub.6 alkyl, particularly an unsubstituted alkyl, particularly a C.sub.1-C.sub.3 alkyl, more particularly a C.sub.1 alkyl, wherein in particularly in case of one of R.sup.5, R.sup.6 or R.sup.7 is OH or NR.sup.3.sub.2 the other two are selected from H or C.sub.1-C.sub.6 alkyl, particularly a C.sub.1-C.sub.3 alkyl.

[0085] In certain embodiments R.sup.1 is in a form of a moiety of a formula (R.sup.5)(R.sup.6)(R.sup.7)C(C?O)O, with each of R.sup.5, R.sup.6 or R.sup.7 being selected independently from a C.sub.1-C.sub.6 alkyl, particularly a C.sub.1-C.sub.3 alkyl or NR.sup.3.sub.2, wherein R.sup.3 is an unsubstituted or substituted C.sub.1-C.sub.6 alkyl, particularly an unsubstituted alkyl, particularly a C.sub.1-C.sub.3 alkyl, more particularly a C.sub.1 alkyl, wherein in particularly in case of one of R.sup.5, R.sup.6 or R.sup.7 is NR.sup.3.sub.2 the other two are selected from H or C.sub.1-C.sub.6 alkyl, particularly a C.sub.1-C.sub.3 alkyl.

[0086] In certain embodiments, the ring opening step is performed in the presence of a base metal, in particular Zn, and a strong acid.

[0087] In certain embodiments, the ring opening step is performed in the presence of a base metal, in particular Zn, and a strong acid, wherein the strong acid is selected from HCl, HBr, H.sub.2SO.sub.4, HNO.sub.3, more particularly the strong acid is HCl.

[0088] In certain embodiments, the ring opening step is performed in the presence of a base metal, in particular Zn, and HCl.

[0089] In certain embodiments, the ring opening step is performed in the presence of Zn and HCl.

[0090] In certain embodiments the ring opening step is performed an organic, polar or nonpolar solvent.

[0091] In certain embodiments the ring opening step is performed in toluene or an alcohol, particularly a C.sub.1-C.sub.6 alcohol, or a mixture thereof.

[0092] In certain embodiments the ring opening step is performed in toluene or an alcohol, particularly a C.sub.1-C.sub.4 alcohol, or a mixture thereof.

[0093] In certain embodiments the ring opening step is performed in a mixture of nonpolar and polar solvents, wherein the ratio between the nonpolar and polar solvents is in between 3:1 to 1:10, more particularly between 1:1 to 1:3.

[0094] In certain embodiments the ring opening step is performed in a mixture toluene and alcohol, wherein the ratio between toluene and the alcohol is in between 3:1 to 1:10, more particularly between 1:1 to 1:3.

[0095] In certain embodiments the ring opening step is performed in a mixture toluene and C.sub.2-C.sub.4 alcohol, wherein the ratio between toluene and the alcohol is in between 3:1 to 1:10, more particularly between 1:1 to 1:3.

[0096] In certain embodiments the ring opening step is performed in a mixture of toluene and ethanol or toluene and propanol, wherein the ratio between toluene and the alcohol is in between 3:1 to 1:10, more particularly between 1:1 to 1:3.

[0097] In certain embodiments R.sup.4 is selected from F, a perfluorinated C.sub.1-C.sub.6 alkyl, C.sub.1-C.sub.6 alkyl, or C.sub.1-C.sub.6 alkyl phenyl. In some embodiments R.sup.4 is selected from F, a perfluorinated C.sub.1-C.sub.3 alkyl, C.sub.1-C.sub.3 alkyl, or C.sub.1-C.sub.3 alkyl phenyl. In some embodiments R.sup.4 is selected from F, methyl, trifluoromethyl, methyl phenyl.

[0098] In certain embodiments the leaving group X is a halogen or OSO.sub.2R.sup.4

[0099] In certain embodiments the leaving group X is a halogen.

[0100] In certain embodiments the leaving group X is Cl.

[0101] In certain embodiments the reducing agent is metal hydride or an organometal hydride.

[0102] In some embodiments the reducing agent is aluminum hydride or a boron hydride or mixtures or complexes containing aluminum hydride or boron hydride.

[0103] In some embodiments the reducing agent is LiAlH.sub.4, Red-Al (Natrium-bis(2-methoxyethoxy)-aluminum hydride) or DIBAL (Diisobutylaluminum hydride) or LiBHEt.sub.3.

[0104] In certain embodiments the leaving group Y is selected from OH, dinitrogen, dialkyl ether, halogen, alkylcarboxylates, perfluoroalkylsulfonates, alkylsulfonates, nitrate, phosphate, amide.

[0105] In certain embodiments the leaving group Y is a halogen.

[0106] In certain embodiments the leaving group Y is Cl.

[0107] A second aspect of the invention are intermediate products of the reaction chain above in form of compounds of general formula (I), formula (II) or formula (III), particularly formula (II) or formula (III),

##STR00014## [0108] wherein R.sup.1 has the same definition as above with the exception that R.sup.1 is not an unsubstituted alkyl

##STR00015## [0109] wherein R.sup.1 has the same definition as above,

##STR00016## [0110] wherein R.sup.1 and Z have the same definition as above.

[0111] These novel compounds can be synthesised in high yields in the abovementioned reactions. Their unique features make them suitable for efficient synthesis of various steroids.

Methods

[0112] One potential route is described in scheme 1:

##STR00017##

Examples Scheme 1

[0113] ##STR00018##

[0114] 13 g of diosgenin was dissolved in 110 ml of pyridine and 4.6 ml of pivaloyl chloride was dropped in. The reaction was mixed for 6 hours in room temperature. After the completion, the reaction was diluted in 250 ml of toluene. Organic phase was washed with 1 M HCl solution (3?150 ml), saturated NH.sub.4Cl solution (1?100 ml), water (1?100 ml) and saturated NaCl. The solution was dehydrated over Na.sub.2SO.sub.4. The product was then repeatedly crystalized, washed and redissolved to increase its purity. The reaction yielded 12.66 g of piv-diosgenin.

##STR00019##

[0115] The entire Piv-diosgenin and 250 g of zinc powder were suspended in 0.5 l of n-propanol/toluene (3:1) and warmed up to 75? C. Hydrochloric acid (37%) was dropped in and the reaction was conducted for 3 hours in 80? C. The solids were separated from liquid and washed with toluene and water. The phases were separated, and the organic phase was washed with water (2?150 ml). Combined phases was extracted with toluene (1?100 ml). Combined organic phase was dehydrated over Na.sub.2SO.sub.4. Product was crystalized overnight. The product was then repeatedly crystalized, washed and redissolved to increase its purity, yielding 10.33 g piv-diosgenin-diol.

##STR00020##

[0116] 10.33 g of piv-diosgenin-diol was added to 100 ml of pyridine. 4.75 ml of methanesulfonyl chloride was slowly added dropwise. The reaction mixture was stirred at room temperature overnight. The reaction mixture was then diluted with 300 ml of ethyl acetate, washed with 1 M HCl (3?200 ml), saturated NH.sub.4Cl solution (1?200), saturated NaCl solution and dried over Na.sub.2SO.sub.4. The solvent was removed on a rotary evaporator and crude product in the form of a white foam was obtained.

##STR00021##

[0117] 4 g (5 equivalents) of lithium aluminum hydride (LAH) were suspended in 50 ml of dry tetrahydrofuran and cooled to 0? C. Piv-diosgenin mesylate was dissolved in 50 ml of dehydrated tetrahydrofuran and slowly added dropwise. The reaction mixture was stirred at RT for 3 h. After no more starting material is detected, the mixture was cooled down to 0? C. and excess LAH was carefully quenched with water (30 ml). The solution was then diluted with ethyl acetate (300 ml) and water (200 ml) and the phases are separated. The organic phase was washed with saturated NH.sub.4Cl solution (1?100 ml), saturated NH.sub.4HCO.sub.3 solution (1?100 ml), water (1?100 ml), saturated NaCl solution and dried over Na.sub.2SO.sub.4. The ethyl acetate was removed on a rotary evaporator. The crude product was dissolved under reflux in 50 ml of MTBE/ethanol solvent mixture (1:2) and left to stand at RT overnight. Cholesterol crystallizes as silky-glossy flakes.

[0118] An alternate route is described in Scheme 2.

##STR00022##

Examples Scheme 2

[0119] N,N-Dimethyl-L-valine (251 mg, 1.2 eq.) in DCM (10 ml) was stirred with dicyclohexylcarbodiimide (386 mg, 1.3 eq.) 17 min at room temperature and subsequently diosgenin (517 mg, 1.0 eq.) and 4-N,N-dimethylaminopyridine (35 mg, 0.2 eq.) were added. After 1 h, the mixture was washed twice with water, dried over MgSO.sub.4 and evaporated. The residue was purified by flash chromatography on silica (pentane/ether 4:1) to obtain the ester (452 mg, 61%).

[0120] A suspension of zinc (7.6 g) and the ester (405 mg) in ethanol (26 ml) was heated to reflux and hydrochloric acid (37%, 8 ml) was added over a period of 1 h. After additional 2 h at reflux, the remaining zinc was filtered off, the filtrate treated with water and extracted with toluene. After drying over MgSO.sub.4 and evaporation, the desired diol (147 mg, 36%) was isolated by flash chromatography on silica (pentane/ether 3:1).

[0121] A solution of the diol (147 mg) in pyridine (1.35 ml) was cooled to 0? C. and methanesulfonyl chloride (0.23 ml, 4 eq.) was added. After 1 h at ambient temperature, the mixture was diluted with ethyl acetate and subsequently washed with 1M aq. HCl, saturated aq. NaHCO.sub.3, and brine. The solution was dried (MgSO.sub.4) and evaporated to give the crude bis-mesylate (215 mg), which was used for the next step.

[0122] Crude bis-mesylate (215 mg) was dissolved in THF (3 ml) and added at room temperature to a suspension of LiAlH.sub.4 (17 mg, 1.5 eq.) in THF (3 ml). After 1 h, another portion of LiAlH.sub.4 (17 mg, 1.5 eq.) was added and the mixture was stirred for an additional hour. The reaction mixture was first quenched with 1M aq. NaOH and then divided between aq. NaK-tartrate and ethyl acetate. The organic layer was dried (MgSO.sub.4) and evaporated. Cholesterol (47 mg, 45% over two steps) was isolated by flash chromatography on silica (pentane/diethyl ether 2:1).

[0123] Other alternative routes are via the protecting group m-(N,N-Dimethylamino)benzoic Acid or a-Hydroxy-iso-butyric Acid.

m-(N,N-Dimethylamino)benzoic Acid Route

[0124] ##STR00023##

[0125] 1 g diosgenin, 0.5 g DCC, 0.2 g 4-DMAP and 0.4 g of m-(N,N-dimethylamino)benzoic acid were stirred in 15 ml of try DCM for 18 hours at room temperature. The mixture was diluted with 20 ml of DCM and was washed with saturated NaHCO.sub.3 solution, saturated NH.sub.4Cl solution, water, and brine. The organic layer was dried over MgSO.sub.4 and the solvent was removed under reduced pressure and the crude product was dried under HV.

?-Hydroxy-iso-butyric Acid Route

[0126] ##STR00024##

[0127] 5 g diosgenin, 40 mg B(OH).sub.3 and 1.5 g of ?-hydroxy-iso-butyric acid was dissolved in 50 ml of toluene and was refluxed for 2 days with a Stork-Dean-trap. The mixture was diluted with 50 ml of toluene and was washed with saturated NaHCO.sub.3 solution, saturated NH.sub.4Cl solution, water, and brine. The organic layer was dried over MgSO.sub.4 and the solvent was removed under reduced pressure. The crude product was flash chromatographed (pentene/ether 1:1) and 3.9 g of a white powder was obtained.