WO2015166462A1 - Method of purifying 3-o-acetyl-11-keto-beta-boswellic acid (akba) - Google Patents
Method of purifying 3-o-acetyl-11-keto-beta-boswellic acid (akba) Download PDFInfo
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- WO2015166462A1 WO2015166462A1 PCT/IB2015/053177 IB2015053177W WO2015166462A1 WO 2015166462 A1 WO2015166462 A1 WO 2015166462A1 IB 2015053177 W IB2015053177 W IB 2015053177W WO 2015166462 A1 WO2015166462 A1 WO 2015166462A1
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- Prior art keywords
- keto
- akba
- boswellic
- extract
- acetyl
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- 238000000034 method Methods 0.000 title claims abstract description 46
- HMMGKOVEOFBCAU-BCDBGHSCSA-N 3-Acetyl-11-keto-beta-boswellic acid Chemical compound C1C[C@@H](OC(C)=O)[C@](C)(C(O)=O)[C@@H]2CC[C@@]3(C)[C@]4(C)CC[C@@]5(C)CC[C@@H](C)[C@H](C)[C@H]5C4=CC(=O)[C@@H]3[C@]21C HMMGKOVEOFBCAU-BCDBGHSCSA-N 0.000 title abstract 7
- HMMGKOVEOFBCAU-UHFFFAOYSA-N AKBA Natural products C1CC(OC(C)=O)C(C)(C(O)=O)C2CCC3(C)C4(C)CCC5(C)CCC(C)C(C)C5C4=CC(=O)C3C21C HMMGKOVEOFBCAU-UHFFFAOYSA-N 0.000 title abstract 6
- 239000002253 acid Substances 0.000 claims abstract description 46
- 150000007513 acids Chemical class 0.000 claims abstract description 41
- 239000000284 extract Substances 0.000 claims abstract description 25
- 239000011347 resin Substances 0.000 claims abstract description 25
- 229920005989 resin Polymers 0.000 claims abstract description 25
- HEDRZPFGACZZDS-UHFFFAOYSA-N Chloroform Chemical compound ClC(Cl)Cl HEDRZPFGACZZDS-UHFFFAOYSA-N 0.000 claims abstract description 16
- 230000021736 acetylation Effects 0.000 claims abstract description 15
- 238000006640 acetylation reaction Methods 0.000 claims abstract description 15
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims abstract description 14
- 239000000203 mixture Substances 0.000 claims abstract description 11
- 238000013375 chromatographic separation Methods 0.000 claims abstract description 9
- 238000004064 recycling Methods 0.000 claims abstract description 8
- 241000894007 species Species 0.000 claims description 13
- 238000004128 high performance liquid chromatography Methods 0.000 claims description 12
- JUJWROOIHBZHMG-UHFFFAOYSA-N Pyridine Chemical compound C1=CC=NC=C1 JUJWROOIHBZHMG-UHFFFAOYSA-N 0.000 claims description 10
- 230000003647 oxidation Effects 0.000 claims description 10
- 238000007254 oxidation reaction Methods 0.000 claims description 10
- 238000000746 purification Methods 0.000 claims description 10
- WFDIJRYMOXRFFG-UHFFFAOYSA-N Acetic anhydride Chemical compound CC(=O)OC(C)=O WFDIJRYMOXRFFG-UHFFFAOYSA-N 0.000 claims description 9
- YMWUJEATGCHHMB-UHFFFAOYSA-N Dichloromethane Chemical compound ClCCl YMWUJEATGCHHMB-UHFFFAOYSA-N 0.000 claims description 9
- NBGQZFQREPIKMG-UHFFFAOYSA-N 3beta-hydroxy-beta-boswellic acid Natural products C1CC(O)C(C)(C(O)=O)C2CCC3(C)C4(C)CCC5(C)CCC(C)C(C)C5C4=CCC3C21C NBGQZFQREPIKMG-UHFFFAOYSA-N 0.000 claims description 8
- 238000003817 vacuum liquid chromatography Methods 0.000 claims description 7
- 235000003717 Boswellia sacra Nutrition 0.000 claims description 6
- 239000007800 oxidant agent Substances 0.000 claims description 6
- 235000012035 Boswellia serrata Nutrition 0.000 claims description 5
- 239000004863 Frankincense Substances 0.000 claims description 5
- 239000000401 methanolic extract Substances 0.000 claims description 5
- UMJSCPRVCHMLSP-UHFFFAOYSA-N pyridine Natural products COC1=CC=CN=C1 UMJSCPRVCHMLSP-UHFFFAOYSA-N 0.000 claims description 5
- 238000006243 chemical reaction Methods 0.000 claims description 4
- JPJALAQPGMAKDF-UHFFFAOYSA-N selenium dioxide Chemical compound O=[Se]=O JPJALAQPGMAKDF-UHFFFAOYSA-N 0.000 claims description 4
- 240000007551 Boswellia serrata Species 0.000 claims description 3
- RYHBNJHYFVUHQT-UHFFFAOYSA-N 1,4-Dioxane Chemical compound C1COCCO1 RYHBNJHYFVUHQT-UHFFFAOYSA-N 0.000 claims description 2
- JHWIEAWILPSRMU-UHFFFAOYSA-N 2-methyl-3-pyrimidin-4-ylpropanoic acid Chemical compound OC(=O)C(C)CC1=CC=NC=N1 JHWIEAWILPSRMU-UHFFFAOYSA-N 0.000 claims description 2
- BCEIUDAMUFAQMG-UHFFFAOYSA-M CC(C)(C)O[Cr](O)(=O)=O Chemical compound CC(C)(C)O[Cr](O)(=O)=O BCEIUDAMUFAQMG-UHFFFAOYSA-M 0.000 claims description 2
- PCLIMKBDDGJMGD-UHFFFAOYSA-N N-bromosuccinimide Chemical compound BrN1C(=O)CCC1=O PCLIMKBDDGJMGD-UHFFFAOYSA-N 0.000 claims description 2
- VHYFNPMBLIVWCW-UHFFFAOYSA-N 4-Dimethylaminopyridine Chemical compound CN(C)C1=CC=NC=C1 VHYFNPMBLIVWCW-UHFFFAOYSA-N 0.000 claims 1
- 230000008569 process Effects 0.000 description 13
- 238000000926 separation method Methods 0.000 description 10
- 239000002904 solvent Substances 0.000 description 10
- 238000002955 isolation Methods 0.000 description 8
- 241001608538 Boswellia Species 0.000 description 6
- NBGQZFQREPIKMG-PONOSELZSA-N Boswellic acid Chemical compound C1C[C@@H](O)[C@](C)(C(O)=O)[C@@H]2CC[C@@]3(C)[C@]4(C)CC[C@@]5(C)CC[C@@H](C)[C@H](C)[C@H]5C4=CC[C@@H]3[C@]21C NBGQZFQREPIKMG-PONOSELZSA-N 0.000 description 6
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 description 6
- 238000013459 approach Methods 0.000 description 6
- 125000002496 methyl group Chemical group [H]C([H])([H])* 0.000 description 6
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical group [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 4
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 4
- 229910052799 carbon Inorganic materials 0.000 description 4
- 150000001875 compounds Chemical class 0.000 description 4
- 239000000126 substance Substances 0.000 description 4
- 238000011282 treatment Methods 0.000 description 4
- 241000717739 Boswellia sacra Species 0.000 description 3
- 238000006742 Retro-Diels-Alder reaction Methods 0.000 description 3
- 125000002777 acetyl group Chemical group [H]C([H])([H])C(*)=O 0.000 description 3
- 238000001460 carbon-13 nuclear magnetic resonance spectrum Methods 0.000 description 3
- 239000000463 material Substances 0.000 description 3
- 125000001434 methanylylidene group Chemical group [H]C#[*] 0.000 description 3
- VLKZOEOYAKHREP-UHFFFAOYSA-N n-Hexane Chemical compound CCCCCC VLKZOEOYAKHREP-UHFFFAOYSA-N 0.000 description 3
- 239000003960 organic solvent Substances 0.000 description 3
- 230000001590 oxidative effect Effects 0.000 description 3
- 230000003110 anti-inflammatory effect Effects 0.000 description 2
- 238000007385 chemical modification Methods 0.000 description 2
- 238000004587 chromatography analysis Methods 0.000 description 2
- 238000007796 conventional method Methods 0.000 description 2
- 238000004992 fast atom bombardment mass spectroscopy Methods 0.000 description 2
- 238000010438 heat treatment Methods 0.000 description 2
- 125000002887 hydroxy group Chemical group [H]O* 0.000 description 2
- 238000002360 preparation method Methods 0.000 description 2
- 238000002953 preparative HPLC Methods 0.000 description 2
- 238000000425 proton nuclear magnetic resonance spectrum Methods 0.000 description 2
- 238000011160 research Methods 0.000 description 2
- 239000000741 silica gel Substances 0.000 description 2
- 229910002027 silica gel Inorganic materials 0.000 description 2
- 238000012360 testing method Methods 0.000 description 2
- FTQDJVZNPJRVPG-VTBKAGBJSA-N (2s,4as,6as,6br,10s,12as,14bs)-10-acetyloxy-2,4a,6a,6b,9,9,12a-heptamethyl-13-oxo-3,4,5,6,6a,7,8,8a,10,11,12,14b-dodecahydro-1h-picene-2-carboxylic acid Chemical compound C([C@@H]1C2=CC(=O)C34)[C@@](C)(C(O)=O)CC[C@]1(C)CC[C@@]2(C)[C@]4(C)CCC1[C@]3(C)CC[C@H](OC(=O)C)C1(C)C FTQDJVZNPJRVPG-VTBKAGBJSA-N 0.000 description 1
- 238000001644 13C nuclear magnetic resonance spectroscopy Methods 0.000 description 1
- XILIYVSXLSWUAI-UHFFFAOYSA-N 2-(diethylamino)ethyl n'-phenylcarbamimidothioate;dihydrobromide Chemical compound Br.Br.CCN(CC)CCSC(N)=NC1=CC=CC=C1 XILIYVSXLSWUAI-UHFFFAOYSA-N 0.000 description 1
- 235000018062 Boswellia Nutrition 0.000 description 1
- 208000003174 Brain Neoplasms Diseases 0.000 description 1
- 206010009944 Colon cancer Diseases 0.000 description 1
- 241000196324 Embryophyta Species 0.000 description 1
- 241000699670 Mus sp. Species 0.000 description 1
- 238000005481 NMR spectroscopy Methods 0.000 description 1
- 206010028980 Neoplasm Diseases 0.000 description 1
- 241000700159 Rattus Species 0.000 description 1
- 229920005654 Sephadex Polymers 0.000 description 1
- 239000012507 Sephadex™ Substances 0.000 description 1
- QAOWNCQODCNURD-UHFFFAOYSA-L Sulfate Chemical compound [O-]S([O-])(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-L 0.000 description 1
- 238000010521 absorption reaction Methods 0.000 description 1
- -1 acetyl methyl Chemical group 0.000 description 1
- 239000012345 acetylating agent Substances 0.000 description 1
- 230000000397 acetylating effect Effects 0.000 description 1
- 239000012675 alcoholic extract Substances 0.000 description 1
- 125000000746 allylic group Chemical group 0.000 description 1
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 1
- 229940121363 anti-inflammatory agent Drugs 0.000 description 1
- 239000002260 anti-inflammatory agent Substances 0.000 description 1
- 230000006907 apoptotic process Effects 0.000 description 1
- 208000006673 asthma Diseases 0.000 description 1
- 239000002012 ayurvedic medicine Substances 0.000 description 1
- 201000011510 cancer Diseases 0.000 description 1
- 125000002915 carbonyl group Chemical group [*:2]C([*:1])=O 0.000 description 1
- 239000003153 chemical reaction reagent Substances 0.000 description 1
- 208000029742 colonic neoplasm Diseases 0.000 description 1
- 238000012790 confirmation Methods 0.000 description 1
- 239000000287 crude extract Substances 0.000 description 1
- 201000010099 disease Diseases 0.000 description 1
- 208000037265 diseases, disorders, signs and symptoms Diseases 0.000 description 1
- 239000006185 dispersion Substances 0.000 description 1
- 229940000406 drug candidate Drugs 0.000 description 1
- 239000012467 final product Substances 0.000 description 1
- 238000003818 flash chromatography Methods 0.000 description 1
- 239000012634 fragment Substances 0.000 description 1
- 238000013467 fragmentation Methods 0.000 description 1
- 238000006062 fragmentation reaction Methods 0.000 description 1
- 230000005484 gravity Effects 0.000 description 1
- 238000003919 heteronuclear multiple bond coherence Methods 0.000 description 1
- 238000000990 heteronuclear single quantum coherence spectrum Methods 0.000 description 1
- 238000002329 infrared spectrum Methods 0.000 description 1
- 230000002401 inhibitory effect Effects 0.000 description 1
- 230000003993 interaction Effects 0.000 description 1
- 150000002576 ketones Chemical group 0.000 description 1
- 208000032839 leukemia Diseases 0.000 description 1
- 229940052961 longrange Drugs 0.000 description 1
- 238000002803 maceration Methods 0.000 description 1
- 239000002207 metabolite Substances 0.000 description 1
- 125000000325 methylidene group Chemical group [H]C([H])=* 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 125000000896 monocarboxylic acid group Chemical group 0.000 description 1
- 230000000144 pharmacologic effect Effects 0.000 description 1
- 230000003389 potentiating effect Effects 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- 238000004366 reverse phase liquid chromatography Methods 0.000 description 1
- 150000003333 secondary alcohols Chemical class 0.000 description 1
- 239000000377 silicon dioxide Substances 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 230000003595 spectral effect Effects 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
- 229910021653 sulphate ion Inorganic materials 0.000 description 1
- 208000024891 symptom Diseases 0.000 description 1
- 150000003505 terpenes Chemical group 0.000 description 1
- UCGZDNYYMDPSRK-UHFFFAOYSA-L trisodium;gold;hydroxy-oxido-oxo-sulfanylidene-$l^{6}-sulfane Chemical compound [Na+].[Na+].[Na+].[Au].OS([S-])(=O)=O.OS([S-])(=O)=O UCGZDNYYMDPSRK-UHFFFAOYSA-L 0.000 description 1
- 150000003648 triterpenes Chemical class 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07J—STEROIDS
- C07J63/00—Steroids in which the cyclopenta(a)hydrophenanthrene skeleton has been modified by expansion of only one ring by one or two atoms
- C07J63/008—Expansion of ring D by one atom, e.g. D homo steroids
Definitions
- This invention relates to a method or a process for producing a fraction enriched upto 100% of 3-0-acetyl-ll-keto- -bosweHic acid from an extract containing a mixture of boswe!lic acids obtained from the gum resin of Boswel!ia species.
- Bosweilia trees are native to Ethiopia, Somalia, India and the Arabian Peninsula. There are a number of different Bosweilia species, and the Bosweilia sacra is the particular plant that is endemic to the Sultanate of Oman, which grows in the southern part of the country (Dhofarzhou).
- the gum resin of Bosweilia species is commonly known as Frankincense and has been used for many years as an anti-inflammatory agent, particularly in traditional Ayurvedic medicine.
- AKBA' acetyl-ll-keto-p-boswellic acid
- AKBA was first isolated at the end of nineteenth century (1898), but the structure confirmation by NMR was only established at the beginning of the twenty first century in 2003. However, ever since AKBA was first isolated at the end of the nineteenth century, there has been growing interest in testing this compound as a potential drug candidate for a number of different diseases,
- AKBA has been indicated in apoptosis of cancer cells, in particular brain tumours and cells affected by leukaemia or colon cancer. AKBA has also been shown to exhibit anti-inflammatory behaviour and AKBA is also thought to decrease the symptoms of asthma.
- the present invention simply utilises a methanolic extract obtained from gum resin of Bosweliia species, which is not subjected to the same acid/base treatments disclosed in WO 2003/074063,
- the method of the present invention utilises recycled chromatographic separation and a unique solvent in the mobile phase, which allows for the purification of AKBA in a single step, using a single solvent. This is compared with conventional approaches in which there are many steps in the chromatographic separation process, which use multiple solvents in order to isolate and purify the AKBA,
- FIG 1 shows the chemical structure of 3-0-acetyl-ll-keto-3-boswellic acid (AKBA),
- FIG 2 shows the six boswellic acids (Bl to B6) present in an extract obtained from the gum resin
- FIG 3 is a flow chart showing the chemical modification and purification steps to enhance the yield of AKBA.
- FIG 4 is a bar graph showing the yield enhancement of AKBA following the isolation steps of the current invention.
- the present invention relates to large scale isolation of the most active boswellic acid, 3-0-acetyl-l l-keto-3-boswellic acid (AKBA) from extracts obtained from the gum resin of Boswe!lia species.
- AKBA 3-0-acetyl-l l-keto-3-boswellic acid
- the present invention is aimed at enriching the concentration of AKBA in the boswellic acids fraction to a desired concentration up to 100% by weight.
- the invention also relates to the process of removing inactive or less potent boswellic acids from the fraction by converting them to AKBA. This is achieved through a combination of chemical reactions and physical separations by chromatographic methods. This method of enriching the concentration of AKBA in the boswellic acids fraction is shown in FIG 3,
- the present invention utilises vacuum liquid chromatography (VLC) to directly obtain the boswellic acids (BAs) cluster from the gum resin of the Bosweliia species without any need for further acid/base treatments.
- VLC vacuum liquid chromatography
- the chemical modification of the crude extract enhances the yield of AKBA via a two-step approach, firstly by oxidation followed by temperature-controlled NEOS microwave-assisted acetylation.
- IMEQS microwave is used to assist acetylation of secondary alcohols.
- the extract obtained from the gum resin of Boswellia species contains a W BA cluster" (which includes BA, ABA, KBA, AKBA) along with some other metabolites.
- W BA cluster which includes BA, ABA, KBA, AKBA
- the BA cluster is converted to a "KBA cluster” (KBA and AKBA), with double enhancement in the overall percentage of AKBA,
- KBA cluster is then subjected to temperature-controlled NEOS microwave assisted (MWA) acetylation, which converts the KBA cluster into the AKBA.
- MWA NEOS microwave assisted
- the method or process of the present invention isolates and purifies AKBA in an extract obtained from the gum resin of Boswellia species, particularly Boswellia sacra using recycled HPLC.
- This method very effectively removes the other boswellic acids closely associated with AKBA, providing quantitative isolation as well as high purity AKBA in the final sample.
- Recycled chromatographic separation allows the recycling of the sample, in part or full, and increases the separation efficiency of the process while keeping the peak dispersion to a minimum.
- the present invention utilises a novel solvent of 1% ethanol blended chloroform in the mobile phase during the separation stage, which provides a very efficient isolation of AKBA.
- the organic solvent extract obtained from the gum resin of Boswellia species contains six boswellic acids. These acids are shown in FIG 2 as Bl, B2, B3, B4, B5 and B6.
- the concentration of AKBA (B2) in the natural boswellic acids fraction ranges from 1 to 10%.
- the present invention demonstrates a significant increase in the percentage of AKBA from the original fraction to the final product.
- the enhancement procedure as well as the purification steps were followed-up by analytical HPLC.
- the crude resin was found to contain around 4% of AKBA, while the methanolic extract contains around 8% AKBA.
- chemical enhancement and recycling preparative HPLC purification 100% purity of the sample was achieved.
- the present invention relates to a method for isolating and purifying 3 ⁇ 0 ⁇ acetyl ⁇ ll-keto ⁇ 3 ⁇ boswellic acid (AKBA) from an extract obtained from the gum resin of Boswellia species containing a mixture of boswellic acids.
- the extract is a methanolic extract obtained by vacuum-liquid chromatography from gum resin of Boswellia species.
- the extract is preferably a Frankincense resin of certified botanical origin obtained from the Dhfoar region in the Sultanate of Oman.
- the boswellic acids in the extract are oxidised, thereby forming a fraction containing keto-boswellic acids.
- these keto-boswellic acids in the fraction are converted into 3-0-acetyl-ll-keto- -boswellic acid (AKBA) by microwave assisted temperature-controlled acetylatlon.
- the fraction is purified by recycled HPLC chromatographic separation, which utilises 1% ethanol blended chloroform in the mobile phase to enrich the concentration of 3 ⁇ 0-acetyl ⁇ ll ⁇ keta ⁇ ⁇ boswellic acid (AKBA) in the fraction.
- AKBA 3 ⁇ 0-acetyl ⁇ ll ⁇ keta ⁇ ⁇ boswellic acid
- the AKBA in the fraction may be enriched up to 100% by weight.
- BAs cluster triterpenic acids
- the difficulty in isolating individual BAs using normal HPLC is due to their close polarity in which the peaks appeared merged.
- Utilizing recycled HPLC the separation of peaks appears from the first cycle. However, good separation that allows isolation is achieved after four cycles.
- the first step in the process or method of the present invention involves the oxidation of the boswellic acid mixture to keto-boswellic acids.
- An oxidant conventionally used for allylic oxidation is preferably used for this step.
- the preferred oxidant used for this step is AZ-Bromosuccinsmide (NBS) and dioxane, but other oxidants with similar characteristics can also be used within the scope of the present invention,
- oxidizing agents such as selenium dioxide in a suitable solvent, sodium dichromate AcQH-AczO or t-butylchromate in CC1 - AcGH-Ac 2 G, CrOs- Pyridine can also be utilised to conduct oxidation step. Dry material obtained after oxidation showed 10-12% by weight AKBA by HPLC analysis.
- the second step of the process or method of the present invention involves conversion of the ll-keto- -boswellic acids obtained from the oxidation step into 3-0-acetyl-ll-ketO" -boswellic acid (AKBA) by microwave assisted acetylation.
- the microwave reactor allowed the selection of energy, solvent and time. Temperature was monitored by an infrared sensor.
- the oxidised keto-boswellic acids, pyridine, 4 ⁇ (dimetbylammo)-pyridine and acetic anhydride in dichloromethane were heated for 1 min.
- the solvent was set for dichloromethane and the power was fixed for 500W as optimum microwave power density.
- the NEOS temperature-controlled (MWATC-NEOS) acetylation is used in this invention for the first time to assist the standard acetylation.
- This method allowed the selection of the solvent and temperature.
- This modification allowed the reduction of time from 4 hours (conventional acetylation) to 1 min and enhancement of yield. Dry material obtained after acetylation showed 30-40% by weight AKBA by HPLC analysis.
- the first step in the process involved acetylation of the boswel!ic acids mixture to acetylated bosweilic acids.
- This step could be executed by any typical acetylating agent like acetic anhydride/pyridine.
- the third step of the process or method of the present invention involves chromatographic separation, specifically by recycling HPLC utilising novel solvent 1% ethanol blended chloroform in the mobile phase.
- AKBA is obtained from the acetylation mixture compared with conventional chromatographic methodology.
- Solid supports such as one or more of silica gel, reversed phase silica, alumina, sephadex and TOYOPEA L ® can be used in the process.
- the present invention utilises recycling HPLC, which allows the removal of the other boswel!ic acids closely associated with AKBA that appeared as shoulders via 4 purification cycles.
- HPLC high-density liquid phase
- HPLC is the preferred separation method
- other chromatographic techniques selected from gravity column, flash chromatography, reversed phase chromatography, preparative high pressure liquid chromatography and the combinations thereof can also be utilised by this invention.
- the samples of various grades of frankincense were collected from different locations in Dhofar.
- the freshly collected air-dried material 500 g was crushed and extracted by maceration in 80% methanol for 10 days (3x5 L).
- the combined methanol extract was evaporated and the concentrated viscous extract (200 g) was fractionated by VLC over silica gel (1.4 kg), and eluted with hexane and gradients of chloroform up to 100% and methanol up to 20%.
- Various sub-fractions and the semi-pure compounds were collected by elutlng the various polarity organic solvents in the order of increasing polarity.
- the semi-pure compounds were subjected to further purification by using recycling preparative HPLC utilizing 1% ethanol blended chloroform.
- the removal of the other boswellic acids closely associated with AKBA that appeared as shoulders was achieved after 4 purification cycles.
- the idea of recycling is to separate the peaks in the chromatogram to allow better separation. The optimum separation was achieved after 4 cycles and the pure compound, AKBA was obtained.
- the pure AKBA showed pink colour on the TLC when sprayed with cerric sulphate reagent followed by heating. This pink colour was changed to dark black on further heating. This observation was indicative of the presence of a terpenoid skeleton of the molecule.
- the El-MS of AKBA showed a molecular son peak at m/z 512.
- the molecular mass was further confirmed through FAB-MS and thus the molecular formula C32H48O5 was deduced by the FAB-MS studies (m/z 511 [M - H] ) combined with 13 C NMR spectral data of AKBA.
- the Retro Diels Alder (RDA) fragmentation was identified by the presence of base peak at m/z 232.
- This RDA fragment is characteristic of ⁇ 12 ursene type triterpenes with COOH group at C-24,
- the IR spectrum showed characteristic absorption bands for hydroxyl group (3410 cm -1 ), carbonyl groups (1735 and 1688 cm -1 ) and the tri-substituted double bond (1628 and 812 cm “1 ),
- the 13 C NMR spectrum (BB, and DEPT) of AKBA showed thirty two signals, including eight methyl, nine methylene, seven methine and eight quaternary carbons (Table 1).
- the oiefinic moiety in the ring-C was confirmed by the presence of signals at ⁇ 165,0 in the 13 C NMR spectrum for quaternary carbons (C-13), and the methine carbon (C-12) at ⁇ 130.5.
- the downfield shift of C-13 and a signal at ⁇ 199.3 in 13 C NMR spectrum indicated the presence of the ⁇ - ⁇ unsaturated system with a!kene and ketone moieties.
- the quaternary carbon at ⁇ 170.2, coupled with the indication of acetyl group in 1 H NMR spectrum also confirmed the presence of acetyl substitution in the molecule.
- H-12 proton showed interactions with C-ll ( ⁇ 199,3), C-13 ( ⁇ 165,0), and C-14 ( ⁇ 43.7), thus indicating the relative positions of these groups in the molecule,
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Abstract
The invention relates to a method for isolating and purifying 3-O-acetyl-11-keto-β- boswellic acid (AKBA) from an extract containing a mixture of boswellic acids obtained from the gum resin ofBoswelliaspecies. The method comprises the steps of oxidising the boswellic acids in the extract to form a fraction containing keto-boswellic acids, converting the keto-boswellic acids in the fraction into 3-0-acetyl-11-keto-β-boswellic acid (AKBA) by acetylation and then purifying the fraction by recycling chromatographic separation utilising 1% ethanol blended chloroform in the mobile phase to enrich the concentration of 3-O-acetyl-11-keto-β-boswellic acid (AKBA).
Description
METHOD OF PURIFYING 3-0-ACETYL-ll-KETO-B-BOSWELLIC ACID
This invention relates to a method or a process for producing a fraction enriched upto 100% of 3-0-acetyl-ll-keto- -bosweHic acid from an extract containing a mixture of boswe!lic acids obtained from the gum resin of Boswel!ia species.
Related Art
Bosweilia trees are native to Ethiopia, Somalia, India and the Arabian Peninsula. There are a number of different Bosweilia species, and the Bosweilia sacra is the particular plant that is endemic to the Sultanate of Oman, which grows in the southern part of the country (Dhofar Province).
The gum resin of Bosweilia species is commonly known as Frankincense and has been used for many years as an anti-inflammatory agent, particularly in traditional Ayurvedic medicine.
In particular, studies that have been carried out have established the antiinflammatory activity of particular alcoholic extracts of the gum resin obtained from Bosweilia serrata in mice and rats.
A detailed study on the structure requirements for boswellic acids indicated that of all the six acids that are contained in the gum resin of Bosweilia species, 3-0- acetyl-ll-keto-p-boswellic acid (hereinafter referenced as "AKBA') shows most pronounced inhibitory activity (Sailer, E, ,, et al, British J. Pharmacology, HZ, 615-618, 1996).
AKBA was first isolated at the end of nineteenth century (1898), but the structure confirmation by NMR was only established at the beginning of the twenty first century in 2003. However, ever since AKBA was first isolated at the
end of the nineteenth century, there has been growing interest in testing this compound as a potential drug candidate for a number of different diseases,
For example, AKBA has been indicated in apoptosis of cancer cells, in particular brain tumours and cells affected by leukaemia or colon cancer. AKBA has also been shown to exhibit anti-inflammatory behaviour and AKBA is also thought to decrease the symptoms of asthma.
However, despite the potential biological and pharmacological importance of AKBA, research and testing has been relatively limited because of difficulties in isolating AKBA via conventional methods. The relatively small amounts of AKBA that can be isolated using conventional methods has resulted in AKBA traditionally having a relatively high price, thereby limiting the use of this molecule for research purposes and particularly for use in commercial pharmaceutical treatments.
One of the most significant hurdles with conventional isolation techniques is that an organic solvent extract of the gum resin of Boswel 'a species contains a total of six different boswellic acids. As such, concentration of AKBA is typically only found in a small amount, commonly in the range of between 1 to 10% by weight.
This low concentration of AKBA presents a particular issue with the large scale isolation of AKBA from the extracts of Boswellia gums resins, which has conventionally been a very difficult and time consuming task.
To date, almost all procedures followed the protocol developed by Winterstein el a/, and Jauch et al., which employ chemical conversions followed by chromatographic separation to enhance the percentage of the AKBA.
One prior art approach that has followed a different approach to the conventional protocol developed by Winterstein et al, and Jauch et al. is disclosed in International patent publication no. WO 2003/074063. This prior publication discloses a preparation of up to 100% 3-0-acety!-ll-keto-3- boswellsc acid from an extract containing a mixture of boswellic acids obtained
from gum resin of a mixture of Bosweliia species. The preparation is obtained by oxidizing the mixture of boswel!ic acids, acetylating the fraction and separating cbromatographically to obtain a fraction enriched in AKBA in an amount between 10-100% by weight,
Prior to the oxidation, acetylation and separation steps, the process disclosed in WO 2003/074063 utilises rigorous acid/base treatments in order to obtain the boswellic acid cluster from the Bosweliia species gum resin.
Summary of the Invention
On the other hand, the present invention simply utilises a methanolic extract obtained from gum resin of Bosweliia species, which is not subjected to the same acid/base treatments disclosed in WO 2003/074063,
Further, the method of the present invention utilises recycled chromatographic separation and a unique solvent in the mobile phase, which allows for the purification of AKBA in a single step, using a single solvent. This is compared with conventional approaches in which there are many steps in the chromatographic separation process, which use multiple solvents in order to isolate and purify the AKBA,
It would be advantageous to provide alternative methods of enriching the concentration of AKBA in the boswellic acids fraction obtained from an extract containing a mixture of boswellic acids to a desired concentration up to 100%. This would overcome at least some of the disadvantages of previously known approaches in this field, or would provide a useful alternative.
These and other advantages are met with the present invention, a broad form of which is set out herein, which additionally discloses optional and preferred aspects of the invention. These embodiments are not necessarily limiting on the invention, which is described fully in this entire document.
FIG 1 shows the chemical structure of 3-0-acetyl-ll-keto-3-boswellic acid (AKBA),
FIG 2 shows the six boswellic acids (Bl to B6) present in an extract obtained from the gum resin,
FIG 3 is a flow chart showing the chemical modification and purification steps to enhance the yield of AKBA.
FIG 4 is a bar graph showing the yield enhancement of AKBA following the isolation steps of the current invention.
Detailed De cri tion
The present invention relates to large scale isolation of the most active boswellic acid, 3-0-acetyl-l l-keto-3-boswellic acid (AKBA) from extracts obtained from the gum resin of Boswe!lia species. The chemical structure of AKBA is shown in FIG 1.
Furthermore, the present invention is aimed at enriching the concentration of AKBA in the boswellic acids fraction to a desired concentration up to 100% by weight. The invention also relates to the process of removing inactive or less potent boswellic acids from the fraction by converting them to AKBA. This is achieved through a combination of chemical reactions and physical separations by chromatographic methods. This method of enriching the concentration of AKBA in the boswellic acids fraction is shown in FIG 3,
In particular, the present invention utilises vacuum liquid chromatography (VLC) to directly obtain the boswellic acids (BAs) cluster from the gum resin of the Bosweliia species without any need for further acid/base treatments. This
approach reduces the number of steps in the purification/isolation process and reduces the loss of the yield of AKBA in the final sample.
The chemical modification of the crude extract enhances the yield of AKBA via a two-step approach, firstly by oxidation followed by temperature-controlled NEOS microwave-assisted acetylation. IMEQS microwave is used to assist acetylation of secondary alcohols.
As shown in FIG 2, the extract obtained from the gum resin of Boswellia species contains a WBA cluster" (which includes BA, ABA, KBA, AKBA) along with some other metabolites. As shown in FIG 3, in the first step of oxidation, the BA cluster is converted to a "KBA cluster" (KBA and AKBA), with double enhancement in the overall percentage of AKBA, This "KBA cluster" is then subjected to temperature-controlled NEOS microwave assisted (MWA) acetylation, which converts the KBA cluster into the AKBA.
The method or process of the present invention isolates and purifies AKBA in an extract obtained from the gum resin of Boswellia species, particularly Boswellia sacra using recycled HPLC. This method very effectively removes the other boswellic acids closely associated with AKBA, providing quantitative isolation as well as high purity AKBA in the final sample. Recycled chromatographic separation allows the recycling of the sample, in part or full, and increases the separation efficiency of the process while keeping the peak dispersion to a minimum. Specifically, the present invention utilises a novel solvent of 1% ethanol blended chloroform in the mobile phase during the separation stage, which provides a very efficient isolation of AKBA.
As discussed above, the organic solvent extract obtained from the gum resin of Boswellia species contains six boswellic acids. These acids are shown in FIG 2 as Bl, B2, B3, B4, B5 and B6.
As shown in FIGS 3 and 4, the concentration of AKBA (B2) in the natural boswellic acids fraction ranges from 1 to 10%. However, the present invention demonstrates a significant increase in the percentage of AKBA from the original fraction to the final product. The enhancement procedure as well as the
purification steps were followed-up by analytical HPLC. The crude resin was found to contain around 4% of AKBA, while the methanolic extract contains around 8% AKBA. After the VLC separation, chemical enhancement and recycling preparative HPLC purification 100% purity of the sample was achieved.
As discussed above, the present invention relates to a method for isolating and purifying 3~0~acetyl~ll-keto~3~ boswellic acid (AKBA) from an extract obtained from the gum resin of Boswellia species containing a mixture of boswellic acids. The extract is a methanolic extract obtained by vacuum-liquid chromatography from gum resin of Boswellia species. The extract is preferably a Frankincense resin of certified botanical origin obtained from the Dhfoar region in the Sultanate of Oman.
During an initial oxidation step, the boswellic acids in the extract are oxidised, thereby forming a fraction containing keto-boswellic acids. In a subsequent acetylatlon step, these keto-boswellic acids in the fraction are converted into 3-0-acetyl-ll-keto- -boswellic acid (AKBA) by microwave assisted temperature-controlled acetylatlon.
Finally, the fraction is purified by recycled HPLC chromatographic separation, which utilises 1% ethanol blended chloroform in the mobile phase to enrich the concentration of 3~0-acetyl~ll~keta~ ~boswellic acid (AKBA) in the fraction. In this final sample, the AKBA in the fraction may be enriched up to 100% by weight.
Boswellic acids exist in frankincense as a cluster of triterpenic acids (BAs cluster) and other trsterpenoids with similar Rf values. The difficulty in isolating individual BAs using normal HPLC is due to their close polarity in which the peaks appeared merged. Utilising recycled HPLC, the separation of peaks appears from the first cycle. However, good separation that allows isolation is achieved after four cycles.
The first step in the process or method of the present invention involves the oxidation of the boswellic acid mixture to keto-boswellic acids. An oxidant conventionally used for allylic oxidation is preferably used for this step. The
preferred oxidant used for this step is AZ-Bromosuccinsmide (NBS) and dioxane, but other oxidants with similar characteristics can also be used within the scope of the present invention, For example, oxidizing agents such as selenium dioxide in a suitable solvent, sodium dichromate AcQH-AczO or t-butylchromate in CC1 - AcGH-Ac2G, CrOs- Pyridine can also be utilised to conduct oxidation step. Dry material obtained after oxidation showed 10-12% by weight AKBA by HPLC analysis.
The second step of the process or method of the present invention involves conversion of the ll-keto- -boswellic acids obtained from the oxidation step into 3-0-acetyl-ll-ketO" -boswellic acid (AKBA) by microwave assisted acetylation. The microwave reactor allowed the selection of energy, solvent and time. Temperature was monitored by an infrared sensor. The oxidised keto-boswellic acids, pyridine, 4~(dimetbylammo)-pyridine and acetic anhydride in dichloromethane were heated for 1 min. The solvent was set for dichloromethane and the power was fixed for 500W as optimum microwave power density.
The NEOS temperature-controlled (MWATC-NEOS) acetylation is used in this invention for the first time to assist the standard acetylation. This method allowed the selection of the solvent and temperature. This modification allowed the reduction of time from 4 hours (conventional acetylation) to 1 min and enhancement of yield. Dry material obtained after acetylation showed 30-40% by weight AKBA by HPLC analysis.
Alternately, the first step in the process involved acetylation of the boswel!ic acids mixture to acetylated bosweilic acids. This step could be executed by any typical acetylating agent like acetic anhydride/pyridine.
The third step of the process or method of the present invention involves chromatographic separation, specifically by recycling HPLC utilising novel solvent 1% ethanol blended chloroform in the mobile phase. In this way, higher grade AKBA is obtained from the acetylation mixture compared with conventional chromatographic methodology. Solid supports such as one or more of silica gel,
reversed phase silica, alumina, sephadex and TOYOPEA L® can be used in the process.
The present invention utilises recycling HPLC, which allows the removal of the other boswel!ic acids closely associated with AKBA that appeared as shoulders via 4 purification cycles. The use of 1% ethanol blended chloroform in the mobile phase, afforded more than 99% pure AKBA via a single purification step using one solvent.
Whilst HPLC is the preferred separation method, other chromatographic techniques selected from gravity column, flash chromatography, reversed phase chromatography, preparative high pressure liquid chromatography and the combinations thereof can also be utilised by this invention.
While the invention has been described with reference to preferred embodiments above, it will be appreciated by those skilled in the art that it is not limited to those embodiments, but may be embodied in many other forms.
In this specification, unless the context clearly indicates otherwise, the word "comprising" is not intended to have the exclusive meaning of the word such as "consisting only of", but rather has the non-exclusive meaning, in the sense of "including at least". The same applies, with corresponding grammatical changes, to other forms of the word such as "comprise", etc.
The following example illustrates one of the best methods of carrying out the process according to this invention.
The samples of various grades of frankincense were collected from different locations in Dhofar. The freshly collected air-dried material (500 g) was crushed and extracted by maceration in 80% methanol for 10 days (3x5 L). The combined methanol extract was evaporated and the concentrated viscous extract (200 g) was fractionated by VLC over silica gel (1.4 kg), and eluted with
hexane and gradients of chloroform up to 100% and methanol up to 20%. Various sub-fractions and the semi-pure compounds were collected by elutlng the various polarity organic solvents in the order of increasing polarity.
The semi-pure compounds were subjected to further purification by using recycling preparative HPLC utilizing 1% ethanol blended chloroform. The removal of the other boswellic acids closely associated with AKBA that appeared as shoulders was achieved after 4 purification cycles. The idea of recycling is to separate the peaks in the chromatogram to allow better separation. The optimum separation was achieved after 4 cycles and the pure compound, AKBA was obtained.
The pure AKBA showed pink colour on the TLC when sprayed with cerric sulphate reagent followed by heating. This pink colour was changed to dark black on further heating. This observation was indicative of the presence of a terpenoid skeleton of the molecule.
The El-MS of AKBA showed a molecular son peak at m/z 512. The molecular mass was further confirmed through FAB-MS and thus the molecular formula C32H48O5 was deduced by the FAB-MS studies (m/z 511 [M - H] ) combined with 13C NMR spectral data of AKBA.
The Retro Diels Alder (RDA) fragmentation was identified by the presence of base peak at m/z 232. This RDA fragment is characteristic of Δ12 ursene type triterpenes with COOH group at C-24, The IR spectrum showed characteristic absorption bands for hydroxyl group (3410 cm-1), carbonyl groups (1735 and 1688 cm-1) and the tri-substituted double bond (1628 and 812 cm"1),
Five tertiary methyls were resonated as singlets in the 1H NMR spectrum of AKBA.The secondary methyl (Chh-29) was observed as doublet at δ 0,78, whereas the other secondary methyl (CH3-3O) was observed as overlap signal with the tertiary methyls. All these observations were indicative of the ursane- type skeleton in the molecule. The olefinic proton (H-12) was observed at δ 5.53 as a broad singlet, whereas the proton geminal to the hydroxyl group was observed at δ 5.28 (1H, m).
Table 1: IMMR Data and Key HHBC Correlations for AKBA
The 13C NMR spectrum (BB, and DEPT) of AKBA showed thirty two signals, including eight methyl, nine methylene, seven methine and eight quaternary carbons (Table 1). The seven methyl signals (C-23 and C-25 to C-30), and one acetyl methyl in the range of δ 13 ppm and 29 ppm, one downfield quaternary carbon (C-24) at δ 181,2 along with one methine carbon (C-3) at δ 73.0, proposed that the compoundis likely to be a boswellic acid derivative. The oiefinic moiety in the ring-C was confirmed by the presence of signals at δ 165,0 in the 13C NMR spectrum for quaternary carbons (C-13), and the methine carbon (C-12) at δ 130.5. The downfield shift of C-13 and a signal at δ 199.3 in 13C NMR spectrum indicated the presence of the α-β unsaturated system with a!kene and ketone moieties. Furthermore, the quaternary carbon at δ 170.2, coupled with the indication of acetyl group in 1H NMR spectrum also confirmed the presence of acetyl substitution in the molecule.
The 1H-13C connectivity was determined through HSQC spectrum and the long- range 1H-13C correlations (HMBC) were helpful for assigning the positions of different sub-structures in the molecule to confirm the final structure. H-3 proton showed long range heteronuclear correlations with C-l (δ 34.6), C-2 (δ 23.5), C- 4 (δ 46.4), CH3-23 (δ 23.8) and C=0 (δ 170.2); H-12 proton showed interactions with C-ll (δ 199,3), C-13 (δ 165,0), and C-14 (δ 43.7), thus indicating the relative positions of these groups in the molecule,
Claims
1. A method for isolating and purifying 3-£ acety!-ll-keto-3- boswellic acid (AKBA) from an extract containing a mixture of boswel!ic acids obtained from the gum resin of Bosweliia species, the method comprising the steps of: oxidising the boswellic acids in the extract, thereby forming a fraction containing keta-boswellic acids; converting the keto-boswellic acids in the fraction into 3-0-acetyl~ll~keto- β-boswellic acid (AKBA) by acetylation; and purifying the fraction by recycled chromatographic separation utilising 1% ethanol blended chloroform in the mobile phase to enrich the concentration of 3-D-acetyl-ll-keto- - boswellic acid (AKBA).
2, A method of claim 1 wherein the extract is obtained from the gum resin of Bosweliia species by vacuum-liquid chromatography (VLC)
3, A method of claim 1 wherein the extract is a methanolic extract obtained from the gum resin of Bosweliia species,
4, A method of claim 1 wherein the extract is obtained from the gum resin of Bosweliia sacra.
5, A method of claim 1 wherein the oxidising agent used in the oxidising step to form the keto-boswellic acids is selected from the group consisting of N- Bromosuccinimide (NBS) or dioxane.
6. A method of claim 1 wherein the oxidizing agent used in the oxidising step to form the keto-boswellic acids is selected from the group consisting of selenium dioxide, sodium dichromate AcOH-Ac20, t-butylchromate and pyridine.
7, A method of claim 1 wherein the keto-boswellic acids in the fraction are converted into 3-0-acetyl-ll-keto-3-boswellic acid (AKBA) by microwave assisted temperature-controlled acetylation.
8. A method of claim 7 wherein the extract was heated for 1 min with a microwave power density of 500W during the acetylation step.
9. A method of claim 8 wherein the extract further includes pyridine, 4- (dimethylamino)--pyridine and acetic anhydride in dichloromethane.
10. A method of claim 1 wherein the fraction is enriched in 3-O-acetyl-ll- keto-3-boswellic acid in the range of 10 to 100% by weight following the oxidation, conversion and purification steps,
11. A method of claim 1 wherein the recycled chromatographic separation is recycling high performance liquid chromatography (HPLC) in which the mobile phase is carried out in a 1H/2H column for four cycles.
12. A method of claim 1 wherein the extract used is a Frankincense resin of certified botanical origin obtained from the Dhofar province in the Sultanate of Oman.
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WO2002085921A2 (en) * | 2001-03-01 | 2002-10-31 | Johann Jauch | Simple method for the synthesis of boswellic acids and derivatives thereof |
WO2003074063A1 (en) | 2002-03-05 | 2003-09-12 | Ganga Raju Gokaraju | A PROCESS FOR PRODUCING A FRACTION ENRICHED UPTO 100 % OF 3-O-ACETYL-11-KETO-β-BOSWELLIC ACID FROM AN EXTRACT CONTAINING A MIXTURE OF BOSWELLIC ACIDS |
WO2003077860A2 (en) * | 2002-03-13 | 2003-09-25 | Biophysica, Inc. | BOSWELLIN COMPOSITIONS ENHANCED WITH 3-β-ACETYL-11-KETO-β-BOSWELLIC ACID (“AKBA”), INDUSTRIAL MANUFACTURE AND THEIR USES |
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WO2002085921A2 (en) * | 2001-03-01 | 2002-10-31 | Johann Jauch | Simple method for the synthesis of boswellic acids and derivatives thereof |
WO2003074063A1 (en) | 2002-03-05 | 2003-09-12 | Ganga Raju Gokaraju | A PROCESS FOR PRODUCING A FRACTION ENRICHED UPTO 100 % OF 3-O-ACETYL-11-KETO-β-BOSWELLIC ACID FROM AN EXTRACT CONTAINING A MIXTURE OF BOSWELLIC ACIDS |
WO2003077860A2 (en) * | 2002-03-13 | 2003-09-25 | Biophysica, Inc. | BOSWELLIN COMPOSITIONS ENHANCED WITH 3-β-ACETYL-11-KETO-β-BOSWELLIC ACID (“AKBA”), INDUSTRIAL MANUFACTURE AND THEIR USES |
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