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{{lowercase title}}
{{chembox
| Verifiedfields = changed
| Watchedfields = changed
| verifiedrevid = 396299902
| Name =β-Sitosterol
| ImageFile = Sitosterol structure.svg
| ImageSize = 240
| ImageAlt = Skeletal formula of sitosterol
| ImageFile1 = Sitosterol-3D-balls.png
| ImageSize1 = 250
| ImageAlt1 = Ball-and-stick model of the sitosterol molecule
| IUPACName = Stigmast-5-en-3β-ol
| SystematicName = (1''R'',3a''S'',3b''S'',7''S'',9a''R'',9b''S'',11a''R'')-1-[(2''R'',5''R'')-5-Ethyl-6-methylheptan-2-yl]-9a,11a-dimethyl-2,3,3a,3b,4,6,7,8,9,9a,9b,10,11,11a-tetradecahydro-1''H''-cyclopenta[''a'']phenanthren-7-ol
| OtherNames = 22,23-Dihydrostigmasterol, β-Sitosterin
|Section1={{Chembox Identifiers
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| ChemSpiderID = 192962
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = S347WMO6M4
| ChEMBL_Ref = {{ebicite|changed|EBI}}
| ChEMBL = 221542
| InChI = 1/C29H50O/c1-7-21(19(2)3)9-8-20(4)25-12-13-26-24-11-10-22-18-23(30)14-16-28(22,5)27(24)15-17-29(25,26)6/h10,19-21,23-27,30H,7-9,11-18H2,1-6H3/t20-,21-,23+,24+,25-,26+,27+,28+,29-/m1/s1
| InChIKey = KZJWDPNRJALLNS-VJSFXXLFBZ
| StdInChI_Ref = {{stdinchicite|correct|chemspider}}
| StdInChI = 1S/C29H50O/c1-7-21(19(2)3)9-8-20(4)25-12-13-26-24-11-10-22-18-23(30)14-16-28(22,5)27(24)15-17-29(25,26)6/h10,19-21,23-27,30H,7-9,11-18H2,1-6H3/t20-,21-,23+,24+,25-,26+,27+,28+,29-/m1/s1
| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
| StdInChIKey = KZJWDPNRJALLNS-VJSFXXLFSA-N
| CASNo_Ref = {{cascite|correct|CAS}}
| CASNo = 83-46-5
| PubChem = 222284
| ChEBI_Ref = {{ebicite|changed|EBI}}
| ChEBI = 27693
| SMILES = O[C@@H]4C/C3=C/C[C@@H]1[C@H](CC[C@]2([C@H]1CC[C@@H]2[C@H](C)CC[C@@H](CC)C(C)C)C)[C@@]3(C)CC4
| MeSHName =
}}
|Section2={{Chembox Properties
| C=29 | H=50 | O=1
| Appearance =
| Density =
| MeltingPtC = 136 to 140
| MeltingPt_ref = <ref>{{Cite journal |last=Oja |first=Vahur |last2=Chen |first2=Xu |last3=Hajaligol |first3=Mohammad R. |last4=Chan |first4=W. Geoffrey |year=2009 |title=Sublimation Thermodynamic Parameters for Cholesterol, Ergosterol, β-Sitosterol, and Stigmasterol |journal=Journal of Chemical & Engineering Data |volume=54 |issue=3 |pages=730–734 |doi=10.1021/je800395m}}</ref>
| BoilingPt =
}}
|Section3={{Chembox Hazards
| MainHazards =
| FlashPt =
| AutoignitionPt =
}}
}}

'''β-Sitosterol''' (''beta''-sitosterol) is one of several [[phytosterol]]s (plant sterols) with [[chemical structure]]s similar to that of [[cholesterol]]. It is a white, waxy powder with a characteristic odor, and is one of the components of the [[food additive]] [[E499]]. Phytosterols are hydrophobic and soluble in alcohols.

==Natural occurrences and food==
β-Sitosterol is widely distributed in the [[plant kingdom]]. It is found in [[vegetable oil]], [[nut (fruit)|nuts]], [[avocado]]s, and derived prepared foods such as [[salad dressing]]s.<ref>{{Cite web |date=2014 |title=Nutrition data: Foods highest in beta-sitosterol per 200 calorie serving |url=http://nutritiondata.self.com/foods-000077000000000000000.html |url-status=live |archive-url=https://web.archive.org/web/20150926020129/http://nutritiondata.self.com/foods-000077000000000000000.html |archive-date=26 September 2015 |access-date=25 September 2015 |publisher=Conde Nast, USDA National Nutrient Database, version SR-21}}</ref> [[Olavius algarvensis]], a species of marine annelid, predominantly incorporate β-sitosterol into their cell membranes instead of cholesterol, though cholesterol is also present in said membranes.<ref name=":0">{{Cite journal |last=Michellod |first=Dolma |last2=Bien |first2=Tanja |last3=Birgel |first3=Daniel |last4=Violette |first4=Marlene |last5=Kleiner |first5=Manuel |last6=Fearn |first6=Sarah |last7=Zeidler |first7=Caroline |last8=Gruber-Vodicka |first8=Harald R. |last9=Dubilier |first9=Nicole |last10=Liebeke |first10=Manuel |date=5 May 2023 |title=De novo phytosterol synthesis in animals |journal=Science |language=en |volume=380 |issue=6644 |pages=520–526 |bibcode=2023Sci...380..520M |doi=10.1126/science.add7830 |issn=0036-8075 |pmc=11139496 |pmid=37141360 |s2cid=248367784}}</ref>

==Human research==
β-Sitosterol is being studied for its potential to reduce [[benign prostatic hyperplasia]] (BPH)<ref name="CR_2000">{{Cite journal |last=Wilt |first=T |last2=Ishani |first2=A |last3=MacDonald |first3=R |last4=Stark |first4=G |last5=Mulrow |first5=C |last6=Lau |first6=J |year=2000 |title=Beta-sitosterols for benign prostatic hyperplasia |journal=The Cochrane Database of Systematic Reviews |volume=2011 |issue=2 |pages=CD001043 |doi=10.1002/14651858.CD001043 |pmc=8407049 |pmid=10796740}}</ref><ref name="Kim_2012">{{Cite journal |last=Kim |first=T. H. |last2=Lim |first2=H. J. |last3=Kim |first3=M. S. |last4=Lee |first4=M. S. |year=2012 |title=Dietary supplements for benign prostatic hyperplasia: An overview of systematic reviews |journal=Maturitas |volume=73 |issue=3 |pages=180–5 |doi=10.1016/j.maturitas.2012.07.007 |pmid=22883375}}</ref> and blood [[cholesterol]] levels.<ref>{{Cite journal |vauthors=Rudkowska I, AbuMweis SS, Nicolle C, Jones PJ |year=2008 |title=Cholesterol-lowering efficacy of plant sterols in low-fat yogurt consumed as a snack or with a meal |journal=J Am Coll Nutr |volume=27 |issue=5 |pages=588–95 |doi=10.1080/07315724.2008.10719742 |pmid=18845709 |s2cid=25733066}}</ref>

==Genetic disorder==
While plant sterols are usually beneficial, there is a rare autosomal recessive genetic disorder [[phytosterolemia]] which causes over-absorption of phytosterols.<ref>{{Cite journal |last=Patel Manoj D. |last2=Thompson Paul D. |year=2006 |title=Phytosterols and Vascular Disease |journal=Atherosclerosis |volume=186 |issue=1 |pages=12–19 |doi=10.1016/j.atherosclerosis.2005.10.026 |pmid=16325823}}</ref>

==Precursor of anabolic steroid boldenone==
Being a steroid, β-sitosterol is a precursor of anabolic steroid [[boldenone]]. [[Boldenone undecylenate]] is commonly used in veterinary medicine to induce growth in cattle but it is also one of the most commonly abused anabolic steroids in sports. This led to suspicion that some athletes testing positive on boldenone undecylenate did not actually abuse the hormone itself but consumed food rich in β-sitosterol.<ref>{{Cite journal |last=G. Gallina |last2=G. Ferretti |last3=R. Merlanti |last4=C. Civitareale |last5=F. Capolongo |last6=R. Draisci |last7=C. Montesissa |year=2007 |title=Boldenone, Boldione, and Milk Replacers in the Diet of Veal Calves: The Effects of Phytosterol Content on the Urinary Excretion of Boldenone Metabolites |journal=J. Agric. Food Chem. |volume=55 |issue=20 |pages=8275–8283 |doi=10.1021/jf071097c |pmid=17844992}}</ref><ref>{{Cite journal |vauthors=Ros MM, Sterk SS, Verhagen H, Stalenhoef AF, de Jong N |year=2007 |title=Phytosterol consumption and the anabolic steroid boldenone in humans: a hypothesis piloted |url=https://hal.archives-ouvertes.fr/hal-00577549/file/PEER_stage2_10.1080%252F02652030701216727.pdf |url-status=live |journal=Food Addit. Contam. |volume=24 |issue=7 |pages=679–84 |doi=10.1080/02652030701216727 |pmid=17613052 |s2cid=38614535 |archive-url=https://web.archive.org/web/20201003011822/https://hal.archives-ouvertes.fr/hal-00577549/file/PEER_stage2_10.1080%252F02652030701216727.pdf |archive-date=2020-10-03 |access-date=2019-07-06}}</ref><ref>{{Cite journal |last=R. Draisci |last2=R. Merlanti |last3=G. Ferretti |last4=L. Fantozzi |last5=C. Ferranti |last6=F. Capolongo |last7=S. Segato |last8=C. Montesissa |year=2007 |title=Excretion profile of boldenone in urine of veal calves fed two different milk replacers |journal=Analytica Chimica Acta |volume=586 |issue=1–2 |pages=171–176 |bibcode=2007AcAC..586..171D |doi=10.1016/j.aca.2007.01.026 |pmid=17386709}}</ref>

==Chemistry==

===Chemical engineering===
The use of β-sitosterol as a chemical intermediate was for many years limited due to the lack of a chemical point of attack on the side-chain that would permit its removal. Extensive efforts on the part of many laboratories eventually led to the discovery of a [[pseudomonas]] [[microbe]] that efficiently effected that transformation. Fermentation digests the entire aliphatic side-chain at carbon 17 to afford a mixture of 17-keto products including [[dehydroepiandrosterone]].<ref>Lenz, G. R.; Kirk-Othmer Encyclopedia of Chemical Technology, 3rd ed., Wiley Interscience, London, 1983, Vol. 21, 645.</ref>

===Synthesis===
Total synthesis of β-sitosterol has not been achieved. However, β-sitosterol has been synthesized from stigmasterol '''1''', which involves a specific hydrogenation of the side-chain of stigmasterol.

The first step in the synthesis forms stigmasterol tosylate '''2''' from stigmasterol '''1''' (95% purity) using p-TsCl, DMAP, and pyridine (90% yield). The tosylate '''2''' then undergoes solvolysis as it is treated with pyridine and anhydrous MeOH to give a 5:1 ratio of i-stigmasterol methyl ether '''3''' (74% yield) to stigmasterol methyl ether '''4''', which is subsequently removed by chromatography. The hydrogenation step of a previously proposed synthesis involved the catalyst Pd/C and the solvent ethyl acetate. However, due to isomerisation during hydrolysis, other catalysts, such as PtO<sub>2</sub>, and solvents, such as ethanol, were tested. There was little change with the use of a different catalyst. Ethanol, however, prevented isomerisation and the formation of the unidentified impurity to give compound '''5'''. The last step of the synthesis is deprotection of the β-ring double bond of '''5''' with p-TsOH, aqueous dioxane, and heat (80 °C) to yield β-sitosterol '''6'''. The cumulative yield for the final two steps was 55%, and the total yield for the synthesis was 37%.<ref>{{Cite journal |last=McCarthy |first=FO |last2=Chopra |first2=J |last3=Ford |first3=A |last4=Hogan |first4=SA |last5=Kerry |first5=JP |last6=O'Brien |first6=NM |last7=Ryan |first7=E |last8=Maguire |first8=AR |year=2005 |title=Synthesis, isolation and characterisation of beta-sitosterol and beta-sitosterol oxide derivatives |journal=Organic & Biomolecular Chemistry |volume=3 |issue=16 |pages=3059–65 |doi=10.1039/b505069c |pmid=16186940}}</ref>

[[Image:Synthesis of sitosterol.gif]]

==Biosynthesis==
[[File:Biosynthsitosterol.png|thumb|150px|Biosynthesis of β-sitosterol (6) from cycloartenol (7)]]

The regulation of the biosynthesis of both sterols and some specific lipids occurs during membrane biogenesis.<ref>{{Cite book |last=Hartmann |first=Marie-Andrée |title=Lipid Metabolism and Membrane Biogenesis |year=2003 |isbn=978-3-540-20752-8 |series=Topics in Current Genetics |volume=6 |pages=183–211 |chapter=5 Sterol metabolism and functions in higher plants |doi=10.1007/978-3-540-40999-1_6}}</ref> Through 13C-labeling patterns, it has been determined that both the mevalonate and deoxyxylulose pathways are involved in the formation of β-sitosterol.<ref>{{Cite journal |last=De-Eknamkul W. |last2=Potduang B. |year=2003 |title=Biosynthesis of β-Sitosterol and Stigmasterol in Croton sublyratus Proceeds Via a Mixed Origin of Isoprene Units |journal=Phytochemistry |volume=62 |issue=3 |pages=389–398 |bibcode=2003PChem..62..389D |doi=10.1016/S0031-9422(02)00555-1 |pmid=12620352}}</ref> The precise mechanism of β-sitosterol formation varies according to the organism, but is generally found to come from [[cycloartenol]].<ref>Dewick, P. M. Medicinal Natural Products: A Biosynthetic Approach. 3 ed.; John Wiley & Sons Ltd.: United Kingdom cyclization, 2009; p 539.</ref>

The biosynthesis of cycloartenol begins as one molecule of [[isopentenyl diphosphate]] (IPP) and two molecules of [[dimethylallyl diphosphate]] (DMAPP) form [[farnesyl diphosphate]] (FPP). Two molecules of FPP are then joined tail-to-tail to yield [[squalene]], a [[triterpene]]. Squalene, through a cyclization reaction with 2,3-oxidosqualene 6 as an intermediate forms cycloartenol.

The double bond of cycloartenol (compound 7 in diagram) is methylated by SAM to give a carbocation that undergoes a hydride shift and loses a proton to yield a compound with a methylene side-chain. Both of these steps are catalyzed by sterol C-24 methyltransferase (Step E1 in diagram). Compound 8 is then catalyzed by sterol C-4 demethylase (E2) and loses a methyl group to produce cycloeucalenol. Subsequent to this, the cyclopropane ring is opened with cycloeucalenol cycloisomerase (E3) to form '''10'''. Compound '''10''' loses a methyl group and undergoes an allylic isomerization to form gramisterol '''11'''. This step is catalyzed by sterol C-14 demethylase (E4), sterol Δ14-reductase (E5), and sterol Δ8-Δ7-isomerase (E6). The last methyl group is removed by sterol demethylase (E7) to form episterol '''12'''. Episterol '''12''' is methylated by SAM to produce a second carbocation, which loses a proton to yield '''13'''. This step is catalyzed by 24-methylenesterol C-methyltransferase (E8). Compound '''13''' now undergoes reduction by NADPH and modifications in the β-ring to form β-sitosterol. An alternative pathway is described for phytosterol synthesis in some animals, a key enzyme responsible is the sterolmethyltransferase (SMT).<ref name=":0" />

==See also==
* [[Charantin]], a β-sitosteryl glucoside found in the [[bitter melon]] plant.

==References==
{{Reflist}}

{{Phytosterols}}
{{Androgen receptor modulators}}
{{Estrogen receptor modulators}}

{{DEFAULTSORT:Sitosterol, β-}}
[[Category:5α-Reductase inhibitors]]
[[Category:Phytoestrogens]]
[[Category:Phytosterols]]

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