Pentacyclic Triterpenes Baran Lab GM 2013-04-27

Q. Michaudel Pentacyclic Triterpenes Baran Lab GM 2013-04-27

Me Me Me Triterpenes (C30): Me * More than 20,000 triterpenes have been isolated thus far. Among them, tetracyclic and pentacyclic triterpenes are the most abundant.

Me Me H CO2H Me Me H R * Triterpenes can be found in their free form (sapogenins), or bound to glycosides HO (saponins). H Me H Me HO HO * Pentacyclic triterpenes are divided into many subgroups: gammaceranes, hopanes, H H lupanes, oleananes, ursanes, etc. based on their carbon skeleton. Me Me Me Me Me corosolic acid β-amyrin, R = Me Me ≥98%, $12,480/g $21,450/g E Isol. Crape-myrtle (Lagerstroemia Tot. synth. (+/–) Johnson, J. Am. Chem. H H H Me H speciosa). Soc. 1993, 115, 515. Me C Isol. Rubber trees. Me Me Me Me Me Me Me H Me Me Me H Me Corey, J. Am. Chem. Soc. 1993, 115, 8873. D erythrodiol, R = CH2OH A H Me H Me H Me $12,550/g B Isol. Olives. H H H Tot. synth. Corey, J. Am. Chem. Soc. 1993, Me Me Me Me Me Me 115, 8873. gammacerane hopane lupane oleanolic acid, R = CO2H ≥97%, $569/g Me Me Me Isol. mistletoe, clove, sugar beet, olive Me Wikimedia Commons leaves, beeches, American Pokeweed (Phytolacca americana)... H H Me Me Tot. synth. Corey, J. Am. Chem. Soc. 1993, 115, 8873. Me Me H Me Me Me H Me H Me Me H Me H Me Me Me Me H H Me Me Me Me Me H Me H H Me oleanane ursane HO H Me Me * Since 1985, Connelly and Hill have been publishing an annual review on the newly Me Me isolated triterpenoids. e.g. Nat. Prod. Rep. 2011, 28, 1087. germanicol O Tot. synth. (+/–) Ireland, Johnson, Me * For an exhaustive review on pentacyclic triterpenes, see Sheng et al., Nat. Prod. J. Am. Chem. Soc. 1970, 92, Me Rep. 2011, 28, 543. 5743. friedelin Van Tamalen, J. Am. Chem. Soc. $297.50/g * Pentacyclic triterpenes are often bioactive (antitumor, antiviral, antidiabetic, 1972, 94, 152. antiinﬂammatory...) and present a huge therapeutic potential. A few compounds like Isol. Cork oak (Quercus suber, Fagaceae). corosolic acid (dietary supplement against diabetes) are already on the market and Tot. synth. (+/–) Ireland, Tetrahedron Lett. several others are under clinical trials or ready to be launched on the market. 1976, 14, 1071. Prices from Sigma-Aldrich, 2013. 1 Q. Michaudel Pentacyclic Triterpenes Baran Lab GM 2013-04-27

* Betulin was one of the ﬁrst isolated natural products * The bark of white birch contains both betulin (ca. 25%) and betulinic acid (ca. in 1788: Lowitz, M. (1788) in Chemische Annalen 0.025%). The latter can be tedious to isolate, and therefore semi-syntheses from Me (Crell, L., ed.) Vol. 2. p. 312. In 1876, Hausmann betulin have been developed. H performed detailed investigations including elemental analysis on betulin: Ann. 1876, 182, 368. For a review on betulin, see Phytochemistry, 1989, 28, 2229. Me Me Me Me H R H H * Betulin shows antitumor and antiviral activity. Birch OH 1. CrO3, H2SO4, H Me bark (10-14% betulin) has been used as an antiseptic H acetone, 0 °C H CO H and in folk medicine against a broad variety of Me Me Me Me 2 HO H diseases. Also, native Americans used red alder bark 2. NaBH4, THF Me Me (containing betulin and lupeol) against poison oak, H Me 56 % H Me insects bites and skin diseases. HO HO lupeol, R = Me H H ≥94% $2,570/g * Betulinic acid is the most biologically active molecule Me Me Synth. Commun., 1997, 27, 1607. Me Me Isol. Husk of Lupin seeds of the family. It was shown to be a selective inhibitor of * As an alternative, an electrochemical oxidation of betulin to betulin aldehyde using a (Lupinus luteus). human melanoma that functions by induction of catalytic amount of TEMPO has been disclosed recently. Subsequent oxidation with Tot. synth. (+/–) Stork, J. Am. apoptosis (Nat. Med. 1995, 1, 1046). Betulinic acid NaClO affords betulinic acid. Chem. Soc. 1971, 93, 4945. also presents anti-HIV activity by inhibiting the 2 maturation of the virus. Some derivatives are part of Corey, J. Am. Chem. Soc., 2009, the current leading natural products for anti-HIV drugs 131, 13928. (Med. Res. Rev. 2000, 20, 323). Me Me betulin, R = CH2OH ≥98% $121.50/g H H OH TEMPO (cat.) Isol. Bark of birch trees (Betula). Me H anodic oxidaton H CHO betulinic acid, R = CO2H Me Me Me Me ≥90% $572/g H ≥98% $4700/g H Me H Me Isol. Bark of birch trees (Betula). Me Me H CO2H HO HO Semi. synth. Ruzicka, Helv. H H Me Me O Me Me Me Me Chim. Acta. 1938, 21, 1706. H Me NaClO2 Synth. Commun. 1997, 27, 1607. 85% (2 steps) HO C O 2 H Me Me Bevirimat (Panacos, then Myriad Genetics), anti-HIV drug, not currently FDA approved. Platinum anode, copper cathode in 40 L apparatus. Pilot plant can produce ca. 1kg/day of betulinic acid Me US patent US 20080308426 A1 H

N. American Herb & Spice Bet-u-Power Birch Bark Extract: Me Me H CO2H "Is the power of raw, wild, remote-source white birch bark. Birch bark is a top source of potent sterols known as betulin H Me and betulinic acid. These sterols are the subject of extensive research and are heart-healthy. Sterols have high electrical HO charge and are needed by cell membranes. Take wild Bet-u- H Power daily for better health." Me Me * As a side note, buchu leaf oil (Agathosma betulina) that you can buy through Sigma- Image and text found on the website www.soap.com Aldrich does not contain any lupane terpenes, but only smaller terpenes (menthone, $16.31 limonene...). 2 Q. Michaudel Pentacyclic Triterpenes Baran Lab GM 2013-04-27

Biosynthesis of pentacyclic triterpenes from squalene or oxidosqualene: * Squalene and oxidosqualene (6 isoprene units) are formed by condensation of two farnesyl pyrophosphate molecules. See Maimone group meeting 2005.

* Many cyclase phases are possible, consequently the structural diversity of the pentacyclic triterpenes is immense. For interesting reviews, see Corey, Liu, Angew. Chem. Int. Ed. 2000, 39, 2812 Matsuda, Phytochemistry, 2004, 65, 261.

* Often for pentacyclic triterpenes, cyclization takes place with an all-chair conformation of the (oxido)squalene.

O * Mutation of only one amino acid can derail the cyclization pathway to another product. + squalene- Enz-AH Enz-AH+ lupeol For instance, Kushiro et al. have engineered lupeol synthase into β-amyrin synthase (J. hopene synthase cyclase Am. Chem. Soc. 2000, 122, 6816). * Finally, ring cleavage can take place after cyclization leading to even more complexity. For a review on unusually cyclized triterpenes, see Domingo et al.: Nat. Prod. Rep. 2009, 26, 115. Me Me Me Me

H H Me H Me Me H Me H HO H Me H H Me H Me H HO H HO H H H H Me Me Me Me deoxydammarenyl dammarenyl α-seco-amyrin cation cation HO H H Me Me Me Me O

H O O H H Me OH H baccharenyl Me Me Me Me Me Me cation O Me H Me O H H Me Me H H H H H Me camelliol B yardenone HO H

hopyl Main synthetic strategies for pentacyclic triterpenes: H cation H lupyl cation AB + DE ––> ABCDE HO CDE ––> BCDE ––> ABCDE H H D(E) ––> ABCD(E) via polyene cyclization (––> ABCDE) hopene lupeol 3 Q. Michaudel Pentacyclic Triterpenes Baran Lab GM 2013-04-27

Early work, syntheses of degradation products: Me Me H Synthesis of 1,8-dimethylpicens and 1,8 dimethyl-2-methoxypicens: Ruzicka, Helv. Chim. Acta, 1937, 20, 1155. O Me Me Ruzicka and coworkers dehydrogenated various pentacyclic triterpenes using Me 1. KOH, MeOH HClO4, O HO Ac O, Me palladium at 305 °C. Starting with oleanolic acid, they obtained 1,8-dimethylpicens and then NH3, Et2O Me 2 AcOH Me starting with β-amyrin, they obtained 1,8-dimethyl-2-methoxypicens. Then, they Me Me Me H synthesized both picens. 2. electrolysis Me OH PhMe name? rt,10% H Me Me Me Me Me 11-16% 1. Br CO2Et (2 steps) R H γ-onocerene Zn, PhMe Prepared in 1 or 2 H Me Me + steps (isomerization) Me Me from sclareol Me 2. Na, EtOH Me 3. HBr O 38% (3 steps) Br O Synthesis of the oleanane skeleton: Tetrahedron Lett. 1962, 10, 429. Me Me Me Me R R Mg, Et2O, 58% Me Me 1. Pd/C, Br 320 °C Me 1. NaOtAm 68% Me Me 2. AlCl CS 2. Li, NH3, 97% HO 3, 2 + 5% (2 steps) Me Me 3. MeLi, Et2O H Me Me Me Me O H Me Me R = H or OMe, yields are given for R = H. Prepared in 4 steps from sclareol Synthesis of pentacyclosqualene: Corey, J. Am. Chem. Soc. 1959, 81, 1739. Me Me Me Me Me Me AlCl3 H CH NO :Et O OH 3 2 2 rt, 35% H Me Me Me 1. diol oxidation Me Me Me + Me Me Me 2. acetic ring closure Me Me H Me Me Me Me 3. Wolff-Kishner Me H H Barton, J. Chem. Soc., 1955, 2639. Me Me Me Me HO H H Me Me γ-onocerene Me Me onocerin These two products have been previously obtained by isomerization of (–)-olean-12-ene For an enantioselective synthesis of onocerin, see Corey, J. Am. Chem. Soc. 2002, 124, 11290. 4 Q. Michaudel Pentacyclic Triterpenes Baran Lab GM 2013-04-27

Relay synthesis of pentacyclic triterpenes: O O 1. Synthesis of hopenone-I: Stork, J. Am. Chem. Soc. 1959, 81, 5516. MgCl Me Me MeO Me Me OMe CO2H Ac2O OMe Me Me O H H Me O O 2. MeLi, MeI, DME Me + 3. H3O O O H H 12 steps 1. Kolbe Me Me B 45% (3 steps) Me C including a HO 2. acetylation AcO resolution H 29% (2 steps) H O Me Me Me Me 2 O OMe H 4 steps 1. Li, NH , EtOH 13 3 Me + Me Me Me H 2. H3O Me Me PPA 31% (2 steps) 90% Me Me Me Me H Me H Me 5 steps HO O H H Me Me Me The α−C13 was also Me Me Arigoni, Helv. Chim. formed, diminishing the O AcO yield of desired product. H Acta 1958, 41, 152. H Me Me Me Me 2 hopenone-I α−onocerin diacetate O O 1. Et3Al, HCN First relay synthesis of a pentacyclic triterpene. + 2. (CH2OH)2, H H H 3. DIBAL–H Total synthesis of pentacyclic triterpenes: – 1. Br2, AcOH 4. N2H4, OH Me Me H Me Me Me H Me + 2. CaCO3, Synthesis of (±) germanicol: Ireland, Johnson, J. Am. Chem. Soc. 1970, 92, 5743. 5. H3O DMA 63% (5 steps) H Me 40% H Me + 1. (CH2OH)2, H (2 steps) Me Me O t HO HO Me 2. EtC(O)CH=CH2 1. Li, NH3, BuOH, MeI H H t Me NaOMe 2. LiAl(O Bu)3H Me Me Me Me O O + 41% (2 steps) 3. H3O O 4. Ac2O, pyr Me Me O + 5. H2, Pd/C, AcOH 1. (CH2OH)2, H Me + 62% (5 steps) 2. H3O H 3. tBuOK, MeI – 4. N2H4, OH 1.O2, hν, Me 1. MeLi, DME Me Me 20% (4 steps) sensitizer, Me Me Me Me 2. H CrO Me CO pyr, LiAlH4 2 4, 2 B Me O H Me 2. CrO 2Py O H 3. SOCl pyr H 3 2, HO 64% (2 steps) 4. p-TsOH, 31 steps (0.1% overall yield) H AcO An alternative route from A to C O H (CH2OH)2, PhH H Me Me Me Me Me Me was developed prior to the one 86% (4 steps) A depicted in 12 steps, 7% overall germanicol yield (vs 9 steps, 25% overall yield) 5 Q. Michaudel Pentacyclic Triterpenes Baran Lab GM 2013-04-27

Total synthesis of pentacyclic triterpenes: Heathcock's studies toward the synthesis of germanicol: J. Org. Chem. 1976, 41, Biomimetic synthesis of germanicol: Van Tamelen, J. Am. Chem. Soc. 1972, 2663; J. Org. Chem., 1976, 41, 2670. Me Me 94, 8229. Me Me O O CO2Et Me Me Me Me 1. H2, Pd/C + Me Me H 2. LiAlH4 EtO C NaBH + EtO OEt EtO2C 2 4 98% E + E O 42% Me then H Me (2 steps) E E O OtBu name? t O 80-85% Me O Cl O BuOK, 80 °C 80% Me Me Me Me Me Me Me Me Me E = CO Et Me Me 1. Ph3P=CH2 2 2. Li, EtNH 1. mCPBA Br 2 Me Me Me Me 3. PBr3 2. Jones 1. H2, Pd/C 2. AlH Et O 1. NaCN, DMSO, BF OEt 3, 2 160 °C 3 2 60% (3 steps) 60% (2 steps) 3. HBr, Et2O PhH, rt, H Me O Me Me 2. NBS, (BzO)2, Δ E 60% 10% (6 steps) E E Me O HO 3. DBN, PhH, rt H Me H Me Heathcock published 5 papers on the synthesis of the fragments AB or DE of pentacyclic Me Br Me Me Me triterpenes but did not complete a synthesis. Arigoni and coworkers used a sample of the bromide intermediate from his laboratory for Me Me SPh an in vitro synthesis of β-amyrin H Me Me Me Br Me 1. THF, –78 °C -amyrin synthase Me Me Me β + H β-amyrin This illustrates the 2. LiNEt2, –78 °C Arigoni H Me Me enzyme's ability to O O 43% (2 steps) generate product Me Me Me O O Me from an artiﬁcial SnCl4 substrate. δ-amyrin van Tamelen Chem. Commun. 1973, 73. Me Me Me Me O Me Me 1. HClO4 Formal enantioselective synthesis of germanicol: Corey, J. Am. Chem. Soc. 2008, H 2. Me 130, 8865. OMe Ph S 2 Li Me Me Me Me Me TBSO SnCl4 Me Me O 1. Me Me Me Et O, –78 °C H Me MeNO2, 0 °C Me 55% (2 steps) TBS 2 Me Me OMe 8% 2. BaI2, –78 °C HO then resolution H Me Me via Mosher O 3. Me Me Me ester Me Br (–)-δ-amyrin O OMe Me Me Me Me O one-pot, 74% Me 5 steps from 1. MeAlCl2, –94 °C H Me hν, p-xylene farnesyl acetate name? 2. TBSCl germanicol 14 steps (0.08% overall yield) t 3. PPA HO BuOH:H2O H 33% (3 steps) Me Me 6 Q. Michaudel Pentacyclic Triterpenes Baran Lab GM 2013-04-27

Relay synthesis of (±)-lupeol: Stork, J. Am. Chem. Soc. 1971, 93, 4945. OH OAc

OH OBz 1. Li, NH tBuOH, 1. benzoylation 1. pTsOH, (CH OH) 3, 2 2 H HMPA, MeI H 2. HC(OAllyl)3 2. LiAlH4 AllylOH, pTsOH 2. pTsOH, (CH OH) H H 3. NaOAc, 2 2 3. pyr, Δ AcOH:THF:MeOH Me Me H Me 3. oxidation Me Me H Me

H 4. Et AlCN H 4. benzoylation 4. NaHMDS, Ac O Me 2 Me H Me 2 H Me 5. NaBH4 O O 63% (4 steps) O CN 52% (5 steps) O prepared in 3 steps D O Me Me Me

OH OBz t 1. Li, NH3, BuOH, MeO2C HMPA, MeI MeO2C OTs H H 2. benzoylation 1. mesylation H H 3. disiamylborane 2. 3% HCl:THF 1. O3, –70 °C H H H 2. NaBH NaOH Me O Me Me Me H Me Me H 4, 4. Jones Me Me + O 3. saponiﬁcation NaHMDS 3. H3O 85% (3 steps) O H Me 52% H Me OH O (10 steps) O 4. CH2N2 5. tosylation O O Me Me Me Me OBz OH

1.MeLi Me H H 2. POCl3, pyr 1. Ac2O, AcCl 1. Li, NH3, AllylBr + H 2. EtMgBr, – 30 °C 2. benzoylation 3. H3O 4. NaBH Me H Me Me H Me 4 3. base Me Me H Me Me 80% (2 steps) O 34% (7 steps) Me Me H Me HO2C O HO 37 steps from a known compound Me Me lupeol to ester relay (2% overall yield) OBz OBz Enantioselective synthesis of lupeol: Corey, J. Am. Chem. Soc. 2009, 131, 13928. 1. pTsOH, (CH2OH)2 OMe OMe 2. 9-BBN 1. EtMgBr, – 30 °C H H OH 2. base 3. Jones OTIPS D 1. MeAlCl Me Me Me 2, Me Me 50% (5 steps) Me Me H Me 4. Ac O, AcCl Me Me H Me Me2AlCl, –78 °C 1. CF CO H 2 3 2 E 2. TBAF H 2. KHCO3, MeOH H Me H Me Me Me Me 3. H2, Pd/C 75% (2 steps) 4. MeLi O O O HO O H Me 41% (4 steps) Me Me prepared in 3 steps from farnesyl acetate 7 Q. Michaudel Pentacyclic Triterpenes Baran Lab GM 2013-04-27

O O H Synthetic approach to analogues of betulinic acid: Jung, Tetrahedron 2006, 62, Me Me 9321. Me Me 1. Li, NH3, –78 °C H TBSO Me Me 2. KOtBu Me Me I Me H 3. TBSCl H Me Me Me PdCl2(dppf), NaOH 83% (3 steps) Me 68% Me HO H TBSO H Me Me Me Me TBSO E H Me Me Me Me Me Me

1. TMS O O OH 1. LiHMDS, 0 °C B 1. MsCl, Et N H Me Pd(dba)2, CuI, PPh3, Et3N TBSO 3 Me 2. TBAF H –20 °C to 0 °C I Me Me 3. TBSOTf, Et3N 2. TBAF Me Me Me Me 4. Cp2Zr(H)Cl, (+)-lupeol catecholborane Me 65% (2 steps) 2. LiBH 0 °C H Me 4, 72% (4 steps) 14 steps from farnesyl 50% (2 steps) TBSO TBSO OTBS hν (quartz), acetate epoxide H H (5% overall yield) benzanthrone, Me Me Me Me Me THF, 84% Me Me Me Me Me Me Me Me Δ or hν Me Me H electrocyclized product H Me TBSO Me Me H Me H Me Me Me Me Me Me Synthesis of (±)-friedelin: Ireland, Tetrahedron Lett. 1976, 14, 1071. H germanicol δ-amyrin 18-epi-β-amyrin OMe OMe CF3SO3H 2 3 4 Me Me Me H Me CDCl3, rt Me Me Me Me + H H Me H H O O 25% (7 steps) Me Me lupeol H Me H Me H Me 1 Me Me EtO O via cyclopropane Me Me Me OMe 1. H2O2, NaOH α-amyrin taraxasterol ψ-taraxasterol Me Me 2. TsNHNH2, 5 6 7 Me AcOH name? after x h at rt 1 2 3 4 5 6 7 H H H 3. MeLi, Et O H H 2 1 h 18% 12% 16% 12% 6% 38% 5% 72% (3 steps) Me Me 7% (16 steps) 2 h 0 12% 18% 12% 8% 42% 5% Me Me 12 h 0 15% 12% 17% 10% 29% 10% O Me Me friedelin 24 h 0 15% 12% 17% 10% 29% 10% Me HO The selectivity of the ﬁrst Birch reduction (ring A) was enabled by selective removal of the Me 8 group (ring E) with Ph2PLi, Birch reduction (A) and remethylation of the untouched phenol (E). Q. Michaudel Pentacyclic Triterpenes Baran Lab GM 2013-04-27

Enantioselective synthesis of serratenediol: Corey, Org. Lett. 2001, 3, 3215. Semi-synthesis strategies: OR Semi-synthesis of myriceric acid: J. Org. Chem. 1997, 62, 960. O Me H Me Me Me Me Me Me Me Me Me Me Me Me Me OH O 1. MeAlCl2, –94 °C O 2. TBAF then KOH O OTBS 1. Jones 3. PhNCO, pyr Me Me H CO H Me Me H 1. MePPh3Br, 2 2. O3 1. NOCl, pyr O Me 51% (3 steps) O Me t O O KO Bu 79% Me Me H Me H Me 2. hυ Me Me 2. AcOH:H2O (2 steps) R = CONHPh 80% Me prepared in 8 steps, 58% overall Me 3. MsCl, pyr HO O (2 steps) yield from farnesyl acetate diol 4. K CO MeOH H oleanolic acid H 2 3, Me Me Me Me 80% (4 steps) OH OR Me Me Me Me Me H Me H Me Me OH O OH O Me 1. MeAlCl2, –78 °C Me O 1. TiCl O Me Me H 2. KOH, MeOH, 100 °C Me Me 3 2. NaNO2, AcOH Me Me H Me Me H H 21% (2 steps) 3. NaOH, MeOH HO 17 steps from farnesyl 1. pTsOH, H H CHO 68% H OH acetate diol O Me (CH2OH)2 Me Me (3 steps) N (5% overall yield) Me 2. Ac2O, pyr O O (–)-serratenediol 3. Li, NH3 H H For a racemic synthesis, see J. Am. Chem. Soc. 1974, 96, 7103. 4. 2N HCl Me Me Me Me 86% (4 steps) Enantioselective synthesis of (+)-seco-C-olenanene: Barrero, J. Org. Chem. 2012, Me Me Me Me 77, 341.

Me Me Me Me H H Me Me CO2H Me Me CO2H H H 1. Cp2TiCl2 (0.3 equiv.), Mn, collidine, H 70% (3 steps) H Me TMSCl, rt Me Me OH O Me Me Me O O H H 2. TBAF Me Me Me Me O Me 44% (2 steps) Me HO stepwise radical HO O Me H Me cyclization Me Me (+)-seco-C-oleanene 14 steps from oleanolic HO prepared in 7 steps, 37% overall yield from Other unusually cyclized triterpenes were acid (26% overall yield) farnesyl acetate diol and Heathcock's/Van obtained as minor products. If Cp2TiCl2 is used myriceric acid Tamelen's bromide bicycle. in substoichiometric amount, other triterpenes are obtained as side products.

9 Q. Michaudel Pentacyclic Triterpenes Baran Lab GM 2013-04-27

Semi-synthesis of 25-acetoxy-3α-hydroxyolean-12-en-28-oic acid: J. Asian. Nat. Semi-synthesis of hypatic acid A: J. Org. Chem. 2007, 72, 3500. Prod. Res. 2008, 10, 271. Me Me Me Me Me Me Me Me 1. Ac O, pyr 2 1. pTsOH, (CH2OH)2 2. Jones 2. NaIO4, RuCl3, 3. NH OH HCl, HO 2 Bu4NBr pyr Me Me H CO2Bn 3. NaBH(Et)3 Me Me H CO2Bn Me Me H CO2Me Me Me H CO2Me HO 50% (3 steps) AcO 72% (3 steps) H Me H Me H Me H Me O HO O HO N H O H H methyl maslinate H Me Me Me Me 1. NOCl, Me Me Me Me Me Me Me Me pyr Me Me 2. hυ 1. Na2PdCl4 3. AcOH, HOAc, KOAc NaNO2 2. DMAP, Et3N, Ac2O HO 4. NaBH4 AcO R=H 3. Pb(OAc)4, HOAc, AcO 5. Ac2O, Me H CO2H Me H CO Bn 1. TiCl3 pyr 2 pyr H 2. KOH Me Me CO2Me 4. NaBH4 1. H2, Pd/C 34% 77% (2 steps) AcO H Me H Me (5 steps) 2. TFA O H Me HO 3. Al(iPrO) R=Ac RO mixture of two products: H 3, O H N AlCl iPrOH 1. KOH H R=H, 23%, (4 steps) Me Me 3, Me Me 2. TiCl3 Me R=Ac, 36% (4 steps) 25-acetoxy-3α-hydroxyolean- 72% (3 steps) 68% (2 steps) 12-en-28-oic acid OAc Semi-synthesis of morolic acid: Tetrahedron 2009, 65, 4304. Me Me Me Me Me Me Me O H H OH H 1. K10 clay, 55° C Me Me H 1. NaBH Me Me O Me Me H CO2Me 4 Me Me H CO2H 2. NaIO4, RuCl3 HO 2. LiBr HO H Me 50% (2 steps) H Me H Me H Me 72% (2 steps) HO Me Me HO O HO H betulin H H H Me Me Me Me Me Me OH OH H 11 steps from methyl maslinate 12 steps from betulin (14% overall yield) (15% overall yield) hyptatic acid A Me Me CO2H 28% (10 steps) H Me HO morolic acid H Me Me 10 Q. Michaudel Pentacyclic Triterpenes Baran Lab GM 2013-04-27

Misc. transformations on pentacyclic triterpenes: Oxidation of lupeol to betulin:

Me Me Me Me

Me Me H H NBS, AIBN, rt 28 CYP450 OH Me Me H CO Me Me Me H CO Me 2 2 Me Me H Me enzyme Me Me H 70% 28 H Me Me patent WO H Me 2012/O29914 A1 H Me HO HO H methyl oleanolate H HO HO Me Me Me Me H H Me Me Me Me

Me Me Microbial models of the mammalian metabolism of betulinic acid

hν Me borosilicate ﬂask H 95% Me Me H CO2Me Me Me H CO2H B. megaterium Me ATCC 13368 H Me Tetrahedron 2004, 60, 1491. HO H Me HO OH Me Me H H Me Me Me TEMPO, O NaOCl, DCM Me Me H CO2H B. megaterium 63% ATCC 14581 Me HO H Me Me H HO Me Me HO H Me Me Me Me Me H CO2H Me [(nBu)3Sn]2O, Br2, HO C. elegans 0°C, 1 min ATCC 9244 H Me Me CO2Me OH HO Me HO OH 62% O H Me Me Me Me Me H HO OH Me Me Me Me H CO2H Me O [(nBu)3Sn]2O, Br2, H Me 0°C, 15 min HO OH Eur. J. Med. Chem. 2012, 56, 237. 57% O H Me Me Me Me

11 Q. Michaudel Pentacyclic Triterpenes Baran Lab GM 2013-04-27

Me Me Me Me Me Me Me H HBr, Ac2O, H AcOH, Me Me OAc PhMe, rt OAc Me Me H Me Me H H H Me Me H Me 21 d, 42% H Me H Me Me Me H Me AcO AcO H H O HO Me Me Me Me H Me Me Me Me alnusenone β-amyrin Me Me Ireland, J. Am. Chem. Soc. 1973, 95, 7829. Johnson, J. Am. Chem. Soc. 1993, 115, 515. 1. mCPBA, Me Me Na2CO3 2. pTsOH, H Johnson's key step en route to β-amyrin: a biomimetic polyene cyclization using a Ac2O, Δ OAc OAc ﬂuorine atom as a cation-stabilizing auxiliary. Me Me Me Me + 44% (2 steps) Me H Me H Me Me Me Me AcO AcO H H Me Me Me Me F Bioorg. Med. Chem. 2010, 18, 2573. F TMS TFA H Me Me Me Me Me Me Other syntheses that have not been discussed in this group meeting: 70% H Me Me Me Me Me Me

HO Me Me

Me Me H R Me Me

H Me H Me HO HO H H Me Me Me Me β-amyrin, R = Me aegiceradienol erythrodiol, R = CH2OH oleanolic acid, R = CO2H Corey, J. Am. Chem. Soc. 1999, 121, 9999. Corey, J. Am. Chem. Soc. 1993, 115, 8873.