Comparative Synthesis of Ingenol Tyler W. Wilson SED Group eting 2.27.07
Ingenol: Biology, Isolation, and istory During WWII a latex was manufactured by precipitating the milky juice of the Euphorbia Ingen (left). The latex was reported to cause extreme skin irritation and blistering. ecker and co-workers later isolated the active principles from the latex and identified ingenol as the key irritant. (+)-Ingenol X-Ray structure was solved in 1970 (coordinates not available) Biological activity includes: tumor-promoting, antileukemia and anti-iv activity
Ingenol: Structure and Synthetic Challenges ighly oxygenated tetracyclic diterpene 1 2 A 3 4 11 D 14 C 12 13 9 10 8 B 7 5 6 (+)-Ingenol 15 Synthetic Challenges: Cis-triol of the AB ring fragment ighly strained in-out stereochemistry of the bicyclo[4.4.1] system
Ingenol: In/ut Isomerism Conformations of bridged bicyclic compounds (C 2 ) k (C 2 ) k C (C 2 ) l (C 2 ) m in, in C C (C 2 ) l (C 2 ) m out, out C (C 2 ) k Y φ φ C C Y (C 2 ) l (C 2 ) m C (C 2 ) k (C 2 ) l (C 2 ) m C (C 2 ) k C (C 2 ) l C 3 (C 2 ) m Angle Definition: C-Y in: φ > 0 C C-Y out: φ < 180 C in, out out, in out,out/in,in isomers are different conformers of the same configuration out,out/in,out isomers have different configurations
Ingenol: In/ut Isomerism Stability of the isomers is dictated by the ring size out out in in in out Δ E (kcal/mol) = 0 10.33 24.71 8 in 8 out Ingenol Δ E (kcal/mol) = 5.9 Epi-Ingenol 0
Ingenol: In/ut Isomerism Conformation dictates the chemistry C C Ac C C (50%) δ in = -3.5 ppm 8 in 8 out Ingenol - Potent tumor promoting agent -anti-leukemic and anti-iv activity Epi-Ingenol -No biological activity
Ingenol: Chronology of Synthetic Efforts 1 2 A 3 4 11 10 ecker: isolation and characterization D 14 C 12 13 (+)-Ingenol 9 B 5 6 8 7 15 Paquette: 1st synthesis of isoingenol (epimeric at C-8) Funk: 1st synthesis of core Winkler: 1st Numerous racemic reports on synthesis core strategies Tanino: 2nd racemic synthesis Wood: 1st asymmetric synthesis Kigoshi: Formal asymmetric synthesis 1968 1988 1993 2004 2003 2002
Ingenol: Funk s Core Synthesis Key Strategy: Ring contraction via Ireland- Claisen rearrangement ecker: isolation and characterization Paquette: 1st synthesis of isoingenol (epimeric at C-8) Funk: 1st synthesis of core Winkler: 1st Numerous racemic reports on synthesis core strategies Tanino: 2nd racemic synthesis Wood: 1st asymmetric synthesis Kigoshi: Formal asymmetric synthesis 1968 1988 1993 2004 2003 2002
Ingenol: Funk s Core Synthesis (+)-carene 1. 3, / 2 S C 2 TiCl 4 2. CeCl 3, C() 3 DCM, -20 C 3. K, C() 2 (29 % over 4 steps) C 2 LiCuCn -78 C (86%) (9.6:6.6:4.5:1) Br TIPS 1. LDA (2 equiv), MPA, TIPS 11 C 2 2. Na, Br C C 2 2 (59 %) C 2 1. F, C 3 CN 2. K, 4h 3. DCC, DMAP Cl (78%) E
Ingenol: Funk s Core Synthesis E LMDS TBSCl -78 C E TBS 1. Toluene, Δ 2. KF, C 3 CN (88 %) E C 2 95:5 dr 4
Ingenol: Funk s Core Synthesis E LMDS TBSCl -78 C E TBS 1. Toluene, Δ 2. KF, C 3 CN (88 %) E C 2 95:5 dr 4
Ingenol: Funk s Core Synthesis 1. (CCl) 2, DMF Na E C 2 2. EtMgBr, CuI, -78 C E 25 C (82%) 91% Et 1:1 mixture 4 E Et LMDS -78 C -> -20 C (90%) 2:1 mixture Z/E 1. DIBAL- 2. Na,, 10 m (56%)
Ingenol: Funk s Core Synthesis TMSCl, Li 2 S TEA, C 3 CN TMS m-cpba DCM, 0 C (37%) 7 6 5 Ingenol Funk Intermediate
Ingenol: Funk s Core Synthesis TMSCl, Li 2 S TEA, C 3 CN TMS m-cpba DCM, 0 C (37%) 7 6 5 Ingenol Funk Intermediate Viable route to optically active tetracyclic core, unable to finish synthesis
Ingenol: Rigby Core Synthesis 1 2 3 4 11 10 12 13 (+)-Ingenol ecker: isolation and characterization 9 5 6 14 8 7 15 Paquette: 1st synthesis of isoingenol (epimeric at C-8) Core strategy developed by Rigby and co-workers Key Strategy: Group Problem! Funk: 1st synthesis of core Winkler: 1st Numerous racemic reports on synthesis core strategies Tanino: 2nd racemic synthesis Wood: 1st asymmetric synthesis Kigoshi: Formal asymmetric synthesis 1968 1988 1993 2004 2003 2002
Ingenol: Rigby Core Synthesis Cr(C) 3 I 1. 1,4-Dioxane, CuCn, Reflux LiCl 2. hν 80% 82% Cr(C) 3 1. s 4 2. DMP, + m-cpba 76% 30% ~70%
Ingenol: Rigby s Core Synthesis Limitations: LiNEt 2 86% Structure of Isolated Intermediate? 1. K, 18-crown-6 2. N 4 Cl (aq.) (68%) LUM chanism? Stereochemistry? M [1,5]-suprafacial sigmatropic rearrangement TMSTf, NEt 3 TMS 81% Ingenol Later reports on [1,5]-rearrangement of a more functionalized intermediate (see ref.)
Ingenol: Rigby s Core Synthesis LiNEt 2 86% LUM 1. K, 18-crown-6 2. N 4 Cl (aq.) (68%) Limitations: M [1,5]-suprafacial sigmatropic rearrangement TMSTf, NEt 3 81% Ingenol Later reports on [1,5]-rearrangement of a more functionalized intermediate (see ref.)
Ingenol: Winkler s Racemic Synthesis 1 2 3 4 11 10 12 13 9 5 6 14 8 7 15 Key Strategy: DeMayo Photocycloaddition ecker: isolation and characterization Paquette: 1st synthesis of isoingenol (epimeric at C-8) Funk: 1st synthesis of core Winkler: 1st Numerous racemic reports on synthesis core strategies Tanino: 2nd racemic synthesis Wood: 1st asymmetric synthesis Kigoshi: Formal asymmetr synthesi 1968 1988 1993 2004 2003 2002
Ingenol: Winkler s Racemic Synthesis C 2 Li Li 1. Li, N TBS 3 TBSTf 2. NEt 3 (69%) (14:1 α:β) 1. LiAl 4 1. LDA, 2 CCN 2. TsCl, NEt 3 2. p-mb 3. MgBr 3. TFAA/TFA/Ac 2, 4. F Acetone (63%) (80%) Cl 1. Se 2, TBP 2. (Cl 3 C) 2 C, PPh 3 (66%)
Ingenol: Winkler s Racemic Synthesis Cl Cl hν C 3 CN Cl 13 Cl 14 43% 17% Propose a mechanism that accounts for the formation of the C-14 chloro-isomer
Ingenol: Winkler s Racemic Synthesis Winkler, J. D. et. al. Synthesis. 2002, 2150
Ingenol: Winkler s Racemic Synthesis Cl Cl hν C 3 CN Cl 13 Cl 14 43% 17% K 2 C 3 (C-6: 7:1 α/β) 6 Cl C 2 1. LiAl 4 2. DBU, 200 C 3. TBSCl, DMAP (35%) TBS 1. CBr3, Na, BnNEt 3 Cl 2. Li, CuSCN, I 3. TBAF (72%)
Ingenol: Winkler s Racemic Synthesis 1. DMP 1. Ac 2, AcCl 2. t-bubr, DMS 2. NBS 3. LiCl, DMF 3. LiCl, DMF (65%) (50%) C C 1. DIBAL- 2. s 4, NM 1. s 4, NM 3. TBDPSCl 4. TESTf (42%) TES TBDPS 2. BzCl (76%) Bz TES TBDPS 1. SCl 2 2. RuCl 3, NaI 4 (79%) Bz 2 S TES TBDPS
Ingenol: Winkler s Racemic Synthesis 2 S Bz TES (R = TBDPS) R 1. DBU 2. 2 S 4 3. TBAF (53%) (66%) Bz R 1. PMB-DMA 2. K 2 C 3 3. DMP PMB R 1. LDA, C 2 CC 2 CCN 2. I, K 2 C 3 3. Pd(Ac) 2 (23%) (28%) R PMB 1. CeCl 3, NaB 4 2. Cl, 3. TBAF (+/-)-Ingenol 1st Synthesis, 43 steps, 80% average yield per
Ingenol: Kuwajima-Tanino Racemic Synthesis Key Strategies: (a) Intramolecular Cyclization. (b) Rearrangement of an Epoxy Alcohol ecker: isolation and characterization Paquette: 1st synthesis of isoingenol (epimeric at C-8) Funk: 1st synthesis of core Winkler: 1st Numerous racemic reports on synthesis core strategies Tanino: 2nd racemic synthesis Wood: 1st asymmetric synthesis Kigoshi: Formal asymmetric synthesis 1968 1988 1993 2004 2003 2002
Ingenol: Kuwajima-Tanino Racemic Synthesis 1. Na, Allyl Bromide 2. CCl 2 C 2, DMF, Δ 1. TESCl, 2. LMDS, ZnBr 2, C 3 C, NBS, 2 Br DMS 3. DBU, Tf 2 (79%) (32%) (67%) Br TES t-buac, LDA, LiBr (91%) R Li t-bu Li C 2t-Bu Br TES 1. 3 Al, LDA, TF 2. Cl (66%) R Br t-bu Al 2 C 2t-Bu 1. TIPSCl 2. LiAl 4 (84%) TIPS
Ingenol: Kuwajima-Tanino Racemic Synthesis 1. S 3 Pyr, DMS, TEA 2. (Et) 2 P()CCl 3, n-buli Cl Cl 1. n-buli, (C 2 ) n 2. Ac 2, NEt 3 3. Co 2 (C) 8 Ac (C) 3 Co Co(C) 3 TIPS (83%) (86%) TIPS TIPS Al(Aryl) 2 Aryl = 2 N (C) 3 Co Co(C) 3 1. Li, N 3 2. CBr 3, Na, BnEt 3 NCl 3. 2 CuLi 2, I TIPS (46%, 4 steps) TIPS
Ingenol: Kuwajima-Tanino Racemic Synthesis TBP, Ti(i-Pr) 4 3 Al TIPS TIPS DCM, -78 C (76%, 2 steps) TIPS L n M M TIPS Pinacol Type Rearragnement
Ingenol: Kuwajima-Tanino Racemic Synthesis TBP, Ti(i-Pr) 4 3 Al TIPS TIPS DCM, -78 C (76%, 2 steps) TIPS 1. DMS, (CCl) 2, NEt 3 2. t-buc(n) 2, DMF 3. DIBAL- (91%) (79%) TIPS 1. NaB 4, Et 2. DIBAL-, 3. Tf 2, 2,6-Lutidine TIPS 1. TBAF 2. PDC, DCM 3. DMF, N N N (83%)
Ingenol: Kuwajima-Tanino Racemic Synthesis 1. CeCl 3, NaB 4 2. TESCl, DMF 3. s 4, Pyr 4. CDI, Toluene (a: 44%, b: 10%) a TES DMAP, Δ (27%) b TES 1. PMP-DMA 2. SCl 2, Pyr. 1. Ac- 2 2. 2 S, NCS (67%, 4 steps) PMP
Ingenol: Kuwajima-Tanino Racemic Synthesis 1. TESTf, 2,6-Lutidine 1. NBS 2. TMSCl, NEt 3 2. F Br TMS TES C 2 I 2, Li (39%, 5 steps) Br 1. Zn, N 4 Cl 2. K, (81%) (+/-)-Ingenol 45 steps in the synthesis with an overall yield of 0.1%
Ingenol: Wood s Asymmetric Synthesis Key Strategy: Ring Closing tathesis ecker: isolation and characterization Paquette: 1st synthesis of isoingenol (epimeric at C-8) Funk: 1st synthesis of core Winkler: 1st Numerous racemic reports on synthesis core strategies Tanino: 2nd racemic synthesis Wood: 1st asymmetric synthesis Kigoshi Formal asymmet synthesi 1968 1988 1993 2004 2003 2002
Ingenol: Wood s Asymmetric Synthesis 1. Ethylene glycol 1. Ac 2 2 C 2. LiAl 4 3. 1M Cl (91%) 2. DBU (76%) BF 3 Et 2, Toluene, -78 C (60%) Grubb's G1 (4 mol%) 1. s 4 /NM Ethylene 2. NaI 4 (98%) 3. Ethylene glycol (73%) Cl PMB K, TF, Δ (98%) PMB
Ingenol: Wood s Asymmetric Synthesis PMB s N N s Cl Ru Cl i-pr (25 mol%) Toluene, Δ (76%) PMB 1. Cl, TF 2. NaB 4, Et 3. I 2, PPh 3 4. KtBu, TF (70%) PMB (38%) 1. Se 2, t-bu 2. DMP, C 2 Cl 2 3. RhCl 3, TMSTf, NEt 3 PMB
Ingenol: Wood s Asymmetric Synthesis KtBu, P() 3, V(acac) 2, 2 tbu (94%) (73%) PMB PMB PMB 1. TMSTf, NEt 3 2. NaB 4, 3. 2,2-DMP, PPTS (62%) PMB 1. DDQ 2. MsCl, NEt 3 3. PhS, Li 2 C 3 4. (N 4 )Mo 7 24, 2 2 (64%) S 2 Ph
Ingenol: Wood s Asymmetric Synthesis S 2 Ph DBU Benzene, Δ (82 % overall) S 2 Ph S 2 Ph DBU 1. Na(g), Na 2 P 4 2. Cl, TF (69%) Se 2 /Si 2 (85%) (+)-Ingenol 1st Asymmetric synthesis, 32 steps from Funk s Keto-ester
Summary and Conclusions Successful strategies for setting in/out stereochemistry: 1 2 A 3 4 11 D 14 C 12 13 9 10 8 B 7 5 6 Ingenol 15 Ireland-Claisen ring contraction (Funk) [1,5]-Suprafacial Sigmatropic Rearrangement (Rigby) Demayo cycloaddition/fragmentation (Winkler) Pinacol type rearrangement of epoxy alcohol (Tanino- Kuwajima) Ring closing metathesis (Wood) Limitations: Strategies lack ability to set in/out stereochemistry of pre-functionalized intermediates Cis-triol requires many late stage manipulations, results in very linear syntheses
References: In/out Isomerization: Alder, R.W.; East, S.P. Chem. Rev. 1996, 96, 2097 Funk Core Synthesis: Funk, R.L. et. al. J. Am. Chem. Soc. 1988, 110, 3298 Funk, R.L. et. al. J. rg. Chem. 1993, 58, 5873 Rigby Core Synthesis: Rigby, J.. et. al. Tetrahedronn Letters 1998, 39, 2265 Rigby, J.. et. al. rg. Lett. 2002, 4, 799 Winkler Synthesis: Winkler, J. D. et. al. Synthesis. 2002, 2150 Winkler, J. D. et. al. J. Am. Chem. Soc. 2002, 124, 9726 Tanino-Kuwajima: Tanino, K et. al. J. rg. Chem. 1997, 62, 3032 Tanino, K et. al. J. Am. Chem. Soc. 2003, 125, 1498 Wood Synthesis: Wood, J. L. et. al. rg. Lett. 2001, 3, 1563 Wood, J. L. et. al. J. Am. Chem. Soc. 2004, 126, 16300 Ingenol Reviews: Winkler, J.D.; Kim, S. Chem. Soc. Rev. 1997, 26, 387 Kuwajima, I.; Tanino, K. Chem. Rev. 2005, 105, 4661 Cha, J. K.; Epstein,. L. Tetrahedron, 2006, 62, 1329 Isolation and Characterization: ecker, E. Cancer Res. 1968, 28, 2338 Zechmeister, K. Tetrahedron Lett. 1970, 4075. pferkuck,. J.; ecker, E. Tetrahedron Lett. 1974, 261.
Winkler Back-up Slide 1. LDA CNC 2 2. p-mb, Dean stark ME TFA/TFAA CF 3
Winkler Back-up Slide PMB R