SYNTHESIS OF PHYTOCANNABINOIDS INCLUDING A DEMETHYLATION STEP

Abstract

A method for demethylating a methylated phytocannabinoid compound of Formula I to form a phytocannabinoid compound of Formula II: Formula I Formula II wherein: R1 is selected from the group consisting of: substituted or unsubstituted C.sub.1-C.sub.5 alkyl; R2 is selected from the group consisting of: OH or O, and R3 is selected from the group consisting of: a substituted or unsubstituted cyclohexene, a substituted or unsubstituted C.sub.2-C.sub.8 alkene, or a substituted or unsubstituted C.sub.2-C.sub.8 dialkene; or R2 is O, and R2 and R3 together form a ring structure in which R2 is an internal ring atom; wherein the method includes: heating a reaction mixture comprising the methylated phytocannabinoid compounds and a polar aprotic solvent in the presence of a dissolved inorganic alkaline salt for a time sufficient to demethylate at least a portion of the methylated phytocannabinoid compounds and form the phytocannabinoid compound.

##STR00001##

Claims

1. A method for demethylating a methylated phytocannabinoid compound of Formula I to form a phytocannabinoid compound of Formula II: ##STR00050## wherein: R1 is selected from the group consisting of: substituted or unsubstituted C.sub.1-C.sub.5 alkyl; R2 is selected from the group consisting of: OH or O, and R3 is selected from the group consisting of: a substituted or unsubstituted cyclohexene, a substituted or unsubstituted C.sub.2-C.sub.8 alkene, or a substituted or unsubstituted C.sub.2-C.sub.8 dialkene; or R2 is O, and R2 and R3 together form a ring structure in which R2 is an internal ring atom; wherein the method includes: heating a reaction mixture comprising the methylated phytocannabinoid compounds and a polar aprotic solvent in the presence of a dissolved inorganic alkaline salt for a time sufficient to demethylate at least a portion of the methylated phytocannabinoid compounds and form the phytocannabinoid compound.

2. A method for the preparation of a phytocannabinoid compound of Formula II comprising: subjecting a first reaction mixture comprising a compound of Formula A and a compound of Formula B in a solvent to reaction conditions such that the compound of Formula A and Formula B together undergo a condensation reaction according to Reaction Scheme I to form a methylated phytocannabinoid compound of Formula I: ##STR00051## wherein: R1 is selected from the group consisting of: substituted or unsubstituted C.sub.1-C.sub.5 alkyl; R2′ is OH R3′ is selected from the group consisting of: a substituted or unsubstituted cyclohexene, a substituted or unsubstituted C.sub.2-C.sub.8 alkene, or a substituted or unsubstituted C.sub.2-C.sub.8 dialkene R2 is R2′ and R3 is R3′; or R2 is O and R2 and R3 together form a ring structure in which R2 is an internal ring atom wherein the method further includes heating a second reaction mixture comprising the methylated phytocannabinoid compound and a polar aprotic solvent in the presence of a dissolved inorganic alkaline salt for a time sufficient to demethylate at least a portion of the methylated phytocannabinoid compounds and form the phytocannabinoid compound according to Reaction Scheme II; ##STR00052##

3. The method of claim 1 or 2, wherein the methylated phytocannabinoid compound is a compound of Formula IA and the phytocannabinoid compound is a compound of Formula IIA: ##STR00053## wherein: R2 is OH and R5 is C(CH.sub.3)═CH.sub.2, or R2 is O and R5 is C(CH.sub.2).sub.2 and R2 and R5 are linked by a covalent bond; and R4 is selected from the group consisting of: C.sub.1-C.sub.4 alkyl, COOH, COOC.sub.1-C.sub.4 alkyl, OC.sub.1-C.sub.4 alkyl, COC.sub.1-C.sub.4 alkyl, tetrahydropyran, benzyl, para-methoxybenzyl, and OH.

4. The method of claim 3, wherein the methylated phytocannabinoid compound is a compound of Formula IB and the phytocannabinoid compound is a compound of Formula IIB: ##STR00054##

5. The method of claim 1 or 2, wherein the methylated phytocannabinoid compound is a compound of Formula IC and the phytocannabinoid compound is a compound of Formula IIC: ##STR00055## wherein: R6 and R7 together form a fused ring structure; R7 and R8 together form a fused ring structure; or R6, R7, and R8 together form a fused ring structure.

6. The method of claim 3 or 5, wherein the methylated phytocannabinoid compound is a compound of Formula ID and the phytocannabinoid compound is a compound of Formula IID: ##STR00056##

7. The method of claim 1 or 2, wherein the methylated phytocannabinoid compound is a compound of Formula IE and the phytocannabinoid compound is a compound of Formula IIE: ##STR00057## wherein: R9 is selected from the group consisting of: a substituted or unsubstituted C.sub.2-C.sub.8 alkene, or a substituted or unsubstituted C.sub.2-C.sub.8 dialkene.

8. The method of claim 2, wherein the first reaction mixture further comprises BF.sub.3.OEt.sub.2.

9. The method of any one of the preceding claims, wherein the dissolved alkaline salt is selected from the group consisting of: Cs.sub.2CO.sub.3, Na.sub.2S, NaOH, or combinations thereof.

10. The method of any one of the preceding claims, wherein the step of heating the reaction mixture includes heating the reaction mixture to a temperature of from about 50° C. to about 100° C.

11. The method of claim 10, wherein the temperature is from about 75° C. to about 95° C.

12. The method of any one of claims 1 to 11, wherein the polar aprotic solvent mixed with up to 30 wt % water.

13. The method of any one of claims 1 to 11, wherein the polar aprotic solvent is selected from the group consisting of: N-methylpyrrolidone, tetrahydrofuran (THF), ethyl acetate (EtOAc), acetone, dimethylformamide (DMF), acetonitrile (MeCN), dimethyl sulfoxide (DMSO), propylene carbonate (PC), and combinations thereof.

14. The method of any one of the preceding claims, wherein a yield of the phytocannabinoid compound is at least 40% based on the weight of the methylated phytocannabinoid compound.

15. The method of claim 14, wherein the yield is at least 50%.

16. The method of any one of the preceding claims, wherein the method further includes separating the phytocannabinoid compound from the polar aprotic solvent.

17. The method of claim 1 or 2, wherein the phytocannabinoid compound is selected from the group consisting of: ##STR00058## ##STR00059## ##STR00060## ##STR00061## ##STR00062##

Description

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0060] The invention relates to methods of demethylating compounds of Formula I to form compounds of Formula II. The invention also more broadly relates to methods of synthesising compounds of Formula I from precursor compounds, and then demethylating the compounds of Formula I to form compounds of Formula II.

[0061] In view of the above, the invention relates to a method for the preparation of a phytocannabinoid compound of Formula II comprising:

[0062] subjecting a first reaction mixture comprising a compound of Formula A and a compound of Formula B in a solvent to reaction conditions such that the compound of Formula A and Formula B together undergo a condensation reaction according to Reaction Scheme I to form a methylated phytocannabinoid compound of Formula I:

##STR00011##

[0063] wherein the method further includes heating a second reaction mixture comprising the methylated phytocannabinoid compound and a polar aprotic solvent in the presence of a dissolved alkaline salt for a time sufficient to demethylate at least a portion of the methylated phytocannabinoid compounds and form the phytocannabinoid compound according to Reaction Scheme II;

##STR00012##

[0064] As used herein, the term “C.sub.1-C.sub.5 alkyl” either used alone or in compound terms refers to straight chain or branched saturated hydrocarbon groups, having 1 to 4 carbon atoms. Suitable alkyl groups include, but are not limited to: methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl, tert-butyl. The “C.sub.1-C.sub.5 alkyl” may be optionally substituted with one or more substituents. The substituents may replace one or more hydrogen atoms on any carbon atom or carbon atoms in the “C.sub.1-C.sub.5 alkyl” carbon atom chain. Preferred substituents include methyl or ethyl groups, and more preferably methyl groups.

[0065] As used herein, the term “C.sub.2-C.sub.8 alkenyl” either used alone or in compound terms refers to straight chain or branched unsaturated hydrocarbon groups, having 2 to 4 carbon atoms and including at least one carbon to carbon double bond, for example, the alkenyl group may be a monoalkenyl group, a diene group, or a triene group. Suitable alkenyl groups include, but are not limited to: ethenyl, propenyl, propadiene, butenyl, butadiene, pentenyl, pentadiene, hexenyl, hexadiene, heptenyl, heptadiene, octenyl, or octadiene groups. The carbon to carbon double bond may be between any two adjacent carbon atoms. The “C.sub.2-C.sub.8 alkenyl” may be optionally substituted with one or more substituents. The substituents may replace one or more hydrogen atoms on any carbon atom or carbon atoms in the “C.sub.2-C.sub.8 alkenyl” carbon atom chain. Preferred substituents include methyl or ethyl groups, and more preferably methyl groups.

[0066] As used herein, the term “demethylation agent” is intended to refer to a compound that is able to cleave the methyl group from the compound of Formula I to form the compound of Formula II. The demethylation agent may be an alkaline salt compound, or an intermediate compound that is formed in a reaction between an alkaline salt compound and an additive or the polar aprotic solvent.

[0067] The method thus provides a mechanism for preparing a large range of different methylated phytocannabinoid compounds from a large range of precursor compounds, which can then be easily demethylated to provide an active phytocannabinoid compound. By way of example, the method of invention can be applied to form the phytocannabinoids outlined in Table 1 below:

TABLE-US-00001 TABLE 1 [00013] Tetrahydrocannabinolic acid THCA (6aR,10aR)-1-hydroxy-6,6,9-trimethyl-3-pentyl- 6a,7,8,10a-tetrahydro-6H-benzo[c]chromene-2- carboxylic acid [00014] Tetrahydrocannabivarinic acid THCVA (6aR,10aR)-1-hydroxy-6,6,9-trimethyl-3-propyl- 6a,7,8,10a-tetrahydro-6H-benzo[c]chromene-2- carboxylic acid [00015] Cannabidiolic Acid (CBDA) (1′R,2′R)-2,6-dihydroxy-5′-methyl-4-pentyl-2′-(prop- 1-en-2-yl)-1′,2′,3′,4′-tetrahydro-[1,1′-biphenyl]-3- carboxylic acid [00016] Cannabidivarinic acid (CBDVA) (1′R,2′R)-2,6-dihydroxy-5′-methyl-2′-(prop-1-en-2- yl)-4-propyl-1′,2′,3′,4′-tetrahydro-[1,1′-biphenyl]-3- carboxylic acid [00017] Cannabigerolic acid (CBGA) (E)-3-(3,7-dimethylocta-2,6-dien-1-yl)-2,4- dihydroxy-6-pentylbenzoic acid [00018] Cannabigerovarinic acid (CBGVA) (E)-3-(3,7-dimethylocta-2,6-dien-1-yl)-2,4- dihydroxy-6-propylbenzoic acid [00019] Cannabichromenic acid (CBCA) 5-hydroxy-2-methyl-2-(4-methylpent-3-en-1-yl)-7- pentyl-2H-chromene-6-carboxylic acid [00020] Cannabichromevarinic acid (CBCVA) 5-hydroxy-2-methyl-2-(4-methylpent-3-en-1-yl)-7- propyl-2H-chromene-6-carboxylic acid [00021] Cannabinolic acid (CBNA) 1-hydroxy-6,6,9-trimethyl-3-pentyl-6H- benzo[c]chromene-2-carboxylic acid [00022] Cannabinovarinic acid (CBNVA) 1-hydroxy-6,6,9-trimethyl-3-propyl-6H- benzo[c]chromene-2-carboxylic acid [00023] Cannabicyclolic acid (CBLA) (1aS,1a.sup.1R,3aR,8bR)-8-hydroxy-1,1,3a-trimethyl-6- pentyl-1a,1a.sup.1,2,3,3a,8b-hexahydro-1H-4- oxabenzo[f]cyclobuta[cd]indene-7-carboxylic acid [00024] Cannabicyclovarinic acid (CBLVA) (1aS,1a.sup.1R,3aR,8bR)-8-hydroxy-1,1,3a-trimethyl-6- propyl-1a,1a.sup.1,2,3,3a,8b-hexahydro-1H-4- oxabenzo[f]cyclobuta[cd]indene-7-carboxylic acid [00025] 11-Hydroxycannabidiolic acid (11-OH-CBDA) (1′R,2′R)-2,6-dihydroxy-5′-(hydroxymethyl)-4- pentyl-2′-(prop-1-en-2-yl)-1′,2′,3′,4′-tetrahydro-[1,1′- biphenyl]-3-carboxylic acid [00026] 11-Hydroxycannabidivarinic acid (11-OH-CBDVA) (1′R,2′R)-2,6-dihydroxy-5′-(hydroxymethyl)-2′-(prop- 1-en-2-yl)-4-propyl-1′,2′,3′,4′-tetrahydro-[1,1′- biphenyl]-3-carboxylic acid [00027] 11-Hydroxytetrahydrocannabinolic acid (11-OH- THCA) (6aR,10aR)-1-hydroxy-9-(hydroxymethyl)-6,6- dimethyl-3-pentyl-6a,7,8,10a-tetrahydro-6H- benzo[c]chromene-2-carboxylic acid [00028] 11-Hydroxytetrahydrocannabivarinic acid (11-OH- THCVA) (6aR,10aR)-1-hydroxy-9-(hydroxymethyl)-6,6- dimethyl-3-propyl-6a,7,8,10a-tetrahydro-6H- benzo[c]chromene-2-carboxylic acid [00029] 11-Carboxycannabidiolic acid (11-COOH-CBDA) (1R,6R)-2′,6′-dihydroxy-4′-pentyl-6-(prop-1-en-2-yl)- 1,4,5,6-tetrahydro-[1,1′-biphenyl]-3,3′-dicarboxylic acid [00030] 11-Carboxycannabidivarinic acid (11-COOH- CBDVA) (1R,6R)-2′,6′-dihydroxy-6-(prop-1-en-2-yl)-4′-propyl- 1,4,5,6-tetrahydro-[1,1′-biphenyl]-3,3′-dicarboxylic acid [00031] 11-Carboxytetrahydrocannabinolic acid (11-COOH- THCA) (6aR,10aR)-1-hydroxy-6,6-dimethyl-3-pentyl- 6a,7,8,10a-tetrahydro-6H-benzo[c]chromene-2,9- dicarboxylic acid [00032] 11-Carboxytetrahydrocannabinolic acid (11-COOH- THCVA) (6aR,10aR)-1-hydroxy-6,6-dimethyl-3-propyl- 6a,7,8,10a-tetrahydro-6H-benzo[c]chromene-2,9- dicarboxylic acid

[0068] Exemplary reaction schemes are provided below:

##STR00033##

##STR00034##

##STR00035##

##STR00036##

##STR00037##

##STR00038##

EXAMPLES

Example 1—Forming Precursor Compounds of Formula B

Example 1A

[0069] ##STR00039##

[0070] A solution of methanol (250 mL) at 0° C. was treated with sodium (12.0 g, 0.52 mol) in portions and stirred until dissolved. Dimethyl malonate (67.7 mL, 0.59 mol) was then added followed by (E)-non-3-en-2-one (59 g, 0.42 mol) and the solution heated at reflux for 8 h. The methanol was removed then diluted with water (400 mL) and washed with CHCl.sub.3 (300 mL). The aqueous later was acidified and extracted with CHCl.sub.3 (3×250 mL). The combined organic layers were dried (MgSO4) and concentrated to give a white solid.

[0071] The white solid (8.17 g, 34.0 mmol) was dissolved in DMF (20 ml) and cooled to 0° C. A solution of Br.sub.2 (1.75 mL, 34.0 mmol) in DMF (6.6 mL) was slowly added and the solution stirred at 20° C. for 1 h. The solution was then heated to 80° C. for 16 h before cooling and treatment with 5% Na.sub.2S.sub.2O.sub.3 aqueous solution (200 mL) and being extracted with ethyl acetate (3×100 mL). The combined organic layers were dried (MgSO.sub.4) and concentrated. The crude material was recrystallized from DCM/hexane to give a white solid.

Example 1B

[0072] ##STR00040##

[0073] A solution of methanol (450 mL) at 0° C. was treated with sodium (25.5 g, 1.11 mol) in portions and stirred until dissolved. Dimethyl malonate (143 mL, 1.25 mol) was then added followed by (E)-hept-3-en-2-one (100 g, 0.89 mol) and the solution heated at reflux for 8 h. The methanol was removed then diluted with water (600 mL) and washed with CHCl.sub.3 (500 mL). The aqueous later was acidified and extracted with CHCl.sub.3 (3×400 mL). The combined organic layers were dried (MgSO.sub.4) and concentrated to give a white solid.

[0074] The white solid (5.37 g, 25.3 mmol) was dissolved in DMF (12 ml) and cooled to 0° C. A solution of Br.sub.2 (1.30 mL, 25.4 mmol) in DMF (6.6 mL) was slowly added and the solution stirred at 20° C. for 1 h. The solution was then heated to 80° C. for 16 h before cooling and treatment with 5% Na.sub.2S.sub.2O.sub.3 aqueous solution (200 mL) and being extracted with ethyl acetate (3×100 mL). The combined organic layers were dried (MgSO.sub.4) and concentrated. The crude material was recrystallized from DCM/hexane to give a white solid.

Example 2—Forming Compounds of Formula I

Example 2A

[0075] ##STR00041##

[0076] R1 is propyl or pentyl.

[0077] A solution of (4R)-1-methyl-4-(prop-1-en-2-yl)cyclohex-2-en-1-ol (1.1 equiv) and methyl 2,4-dihydroxy-6-pentylbenzoate (1 equiv) or methyl 2,4-dihydroxy-6-propylbenzoate (1 equiv) and MgSO.sub.4 (3 equiv) in DCM (0.1 M) at −20° C. was treated with BF.sub.3.OEt.sub.2 (0.1 equiv) in DCM (0.1 M) and stirred for 0.25 h. Water was added followed and extracted with DCM, dried (MgSO.sub.4) and concentrated. The residue was subjected to flash column chromatography (silica, 0 to 5% EtOAc/Hexane gradient elution) to give a colourless oil. Yields 30-40%.

Example 2B

[0078] ##STR00042##

[0079] R1 is propyl or pentyl.

[0080] A solution of (4R)-1-methyl-4-(prop-1-en-2-yl)cyclohex-2-en-1-ol (1 equiv) and methyl 2,4-dihydroxy-6-pentylbenzoate (1 equiv) or methyl 2,4-dihydroxy-6-propylbenzoate (1 equiv) in chlorobenzene (0.1 M) at room temperature was treated with BF3.OEt.sub.2 (0.15 equiv) in chlorobenzene (0.05 M). The solution was stirred for 1 h then treated with aqueous NaHCO.sub.3 and extracted with DCM, dried (MgSO.sub.4) and concentrated. The residue was subjected to flash column chromatography (silica, 0 to 10% EtOAc/Hexane gradient elution) to give a colourless oil. Yields 60-70%

Example 2C

[0081] ##STR00043##

[0082] R1 is propyl or pentyl.

[0083] A solution of methyl (1′R,2′R)-2,6-dihydroxy-5′-methyl-4-pentyl-2′-(prop-1-en-2-yl)-1′,2′,3′,4′-tetrahydro-[1,1′-biphenyl]-3-carboxylate (1 equiv) or methyl (1′R,2′R)-2,6-dihydroxy-5′-methyl-4-pentyl-2′-(prop-1-en-2-yl)-1′,2′,3′,4′-tetrahydro-[1,1′-biphenyl]-3-carboxylate (1 equiv) in DCM (0.1 M) at −20° C. was treated with BF3.OEt.sub.2 (0.1 equiv) in DCM (0.05 M) and stirred for 1 h as it slowly warmed to 0° C. NaHCO.sub.3 in water was added and the aqueous phase extracted with DCM, dried (MgSO.sub.4) and concentrated. The residue was subjected to flash column chromatography (silica, 0 to 5% EtOAc/Hexane gradient elution) to give a colourless oil. Yields 50-55%

Example 2D

[0084] ##STR00044##

[0085] R1 is propyl or pentyl.

[0086] A solution of geraniol (1 equiv) and methyl 2,4-dihydroxy-6-pentylbenzoate (3 equiv) or methyl 2,4-dihydroxy-6-propylbenzoate (3 equiv) in CHCl.sub.3 (0.1 M) at −20° C. was treated with BF.sub.3.OEt.sub.2 (0.1 equiv) in CHCl.sub.3 (0.1 M) and stirred for 0.25 h. Water was added followed and extracted with DCM, dried (MgSO.sub.4) and concentrated. The residue was subjected to flash column chromatography (silica, 0 to 5% EtOAc/Hexane gradient elution) to give a colourless oil. Yields 30-40%.

Example 2E

[0087] ##STR00045##

[0088] R1 is propyl or pentyl.

[0089] A solution of citral (3 equiv), 2,4-dihydroxy-6-pentylbenzoate (1 equiv) or methyl 2,4-dihydroxy-6-propylbenzoate (1 equiv) and Ca(OH).sub.2 (1 equiv) in methanol (0.5 M) in a sealed tube was heated at 140° C. for 1.5 h. The cooled solution was diluted with EtOAc and 1 M HCl. The separated aqueous phase was extracted with EtOAc and the combined organic layers were dried (MgSO.sub.4) and concentrated. The residue was subjected to flash column chromatography (silica, 30% DCM/Hexane elution) to give a colourless oil. Yields 75-85%.

Example 2F

[0090] ##STR00046##

[0091] R1 is propyl or pentyl.

Example 3—Demethylation of Compounds of Formula I to Form Compound of Formula II According to Reaction Scheme II

[0092] ##STR00047##

Example 3A

[0093] A solution of the methyl ester (1 equiv) in DMF (0.25 M) was treated with thiophenol (1.5 equiv) followed by Cs.sub.2CO.sub.3 (0.5 equiv) and stirred at 85° C. for 24 h. The cooled solution was acidified with 1 M HCl to pH 3 and extracted with EtOAc (3 times). The combined organic phases were dried (MgSO.sub.4) and concentrated and the residue was subjected to flash column chromatography (silica, 0 to 20% EtOAc/Hexane gradient elution) to give the desired acid. Yields 60-80%.

[0094] THCA, THCVA, CBDA, CBDVA, CBGA, and CBGA have all been successfully synthesised using the method outlined in Example 3A.

Example 3B

[0095] A solution of the methyl ester (1 equiv) in DMF (0.5 M) was treated with Na.sub.2S.9H.sub.2O (10 equiv) stirred at reflux for 24 h. The cooled solution was acidified with 1 M HCl to pH 3 and extracted with EtOAc (3 times). The combined organic phases were dried (MgSO.sub.4) and concentrated and the residue was subjected to flash column chromatography (silica, 0 to 20% EtOAc/Hexane gradient elution) to give the desired acid. Yields 50-70% but purification is simpler than with Example 3A.

[0096] THCA, THCVA, CBDA, CBDVA, CBGA, and CBGA have all been successfully synthesised using the method outlined in Example 3B.

Example 3C

[0097] A solution of the methyl ester (1 equiv) in DMSO/20% aqueous NaOH (4:1) (0.2 M) was stirred at 80° C. for 24 h. The cooled solution was acidified with 1 M HCl to pH 3 and extracted with EtOAc (3 times). The combined organic phases were dried (MgSO.sub.4) and concentrated and the residue was subjected to flash column chromatography (silica, 0 to 20% EtOAc/Hexane gradient elution) to give the desired acid. Yields 50-70% but purification is simpler than with Example 3A.

[0098] Compounds formed according to the methods of Examples 3A, 3B, and 3C:

##STR00048## ##STR00049##

[0099] CBCA, CBCVA, CBLA, and CBLVA have all been successfully synthesised using the method outlined in Example 3A.

Example 3D

[0100] The inventors have conducted a number of further experiments. Demethylation of compounds of Formula I to compounds of Formula II has been successfully achieved using Na.sub.2S in THF and MeCN. However, the following reagents and reaction conditions were found to be unsuccessful in demethylating compounds of Formula I to form compounds of Formula II:

[0101] LiOH, MeOH/H.sub.2O room temperature to reflux; LiOH, EtOH/H.sub.2O room temperature to reflux; NaOH, MeOH/H.sub.2O room temperature to reflux; NaOH, EtOH/H.sub.2O room temperature to reflux; KOH, EtOH/H.sub.2O room temperature to reflux; Lil, pyridine reflux; LiCl, DMF, 120° C.; Ba(OH).sub.2.8H.sub.2O, MeOH, room temperature reflux; (Bu.sub.3Sn).sub.2O, toluene, reflux; KOtBu, DMSO, 80-100° C.

[0102] These reactions were all unsuccessful in forming CBDA. Further, attempts to form CBGA and THCVA using LiOH in MeOH/H.sub.2O and NaOH in EtOH/H.sub.2O were also unsuccessful.

[0103] It will be understood that the invention disclosed and defined in this specification extends to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings. All of these different combinations constitute various alternative aspects of the invention.