Talk:Todd:Catalytic, Asymmetric Pictet-Spengler Reaction

Use this page for discussion. Preface questions/comments with initials. Reply to questions but don't delete the question. If things are resolved, move them to the "resolved" section at the bottom of the page.

General Things that Need Doing

1. Papers below need looking at - whether to include or not
2. More papers might be relevant. Can do citation searches on papers already included, or new searches.
3. Papers that are already in the review, and have been summarized, need checking (see Quality Control, below for what's needed)
4. Insert DOI link for any paper lacking them on this page, formatted like this: Stoeckigt and Waldmann Angew 2011

Some specific things that currently need doing:
1. Need examples of important bioactive molecules and commercial molecules, e.g. drugs, that can be made with the PS.
2. Intro needs polishing off.

Small things that are needed:
1. Can anyone source a translation of the original Pictet-Spengler article? 10.1002/cber.19110440309. MHT - would be nice to see exactly how it is described there, yes. KAB - translation in progress!

Please don't use email if at all possible. Use this page or some other public forum. Remember if you want to contribute you are going to need an account on OWW and one on Mendeley where we are collecting citations. There is a shared Dropbox folder for access to all Chemdraw files and PDFs - for access contact Murray

General Comments, either on science or the review more broadly

Suggestions can go directly here or on the main page in italics. Minor comments can go in the sandbox area below.

1. Length: the page is quite long, but easier to leave as-is than split the page.
2. Molecule numbering: will happen at the end of the writing process.
3. Yield/ee terminology: Very high = 90+, high = 80+, good = 70+, moderate = 60+.
4. Plagiarism: make sure that no phrases are ever lifted directly from any paper.
5. Inserting schemes: On any page, on the left panel, under tool-box, you will need to select "Upload File." From there you upload the .png file from your computer. Copy the name of the file when it's uploaded (If you're unsure of the file naming convention, click anyone of the scheme .png's and it'll have the details there). Be careful if your file has the same name as an existing one - consider using a different name. Once you've uploaded the file you just need to edit the page where you'd like it to appear. Find the code for some previously uploaded scheme (doesn't matter which), copy and paste it to where you want to put your scheme, and just replace the name of the file you copied, with the name of your file that you just uploaded. Be careful to include .png and be careful of the spacing, there shouldn't be any within the file name. From there, just replace the title of the previous scheme with the details of your scheme. It's important that you only change the words and none of the punctuation that you may see in the code, e.g. "" or |. Just to check if it's alright, you may want to preview before you post. As always with wikis - use other peoples' examples.

MHT - Jan 21 - In the 2007 Hiemstra work, why does the sulfenyl help? Paper says should stabilize intermediate iminium ion and favour cyclization over competitive enamine formation) Paper gives: The use of N-sulfenyl substituents as protecting groups is known in peptide synthesis; see a) L. Zervas, D. Borovas, E. Gazis, J. Am. Chem. Soc. 1963, 85, 3660 – 3666 ; for reviews on sulfenamide chemistry, see b) F. A. Davis, U. K. Nadir, Org. Prep. Proced. Int. 1979, 11, 33–51; c)L. Craine, M. Raban, Chem. Rev. 1989, 89, 689 – 712 ; d) I. V. Koval, Russ. Chem. Rev. 1996, 65, 452 – 473.

MHT - Jan 22 - This paper is listed in the references, but has it been read and digested, to extract a) relevant info about the PS, but mainly b) mechanistic ideas of relevance? If not, leave the ref where it is, but add note in mech section about the need to include it there. Small-Molecule H-Bond Donors in Asymmetric Catalysis, A. G. Doyle and E. N. Jacobsen, Chem. Rev. 2007, 107, 5713-5743.

Sandbox area for minor/temporary comments

This is the place to chat. Use initials for your comments/questions. Inactive chats/resolved things can be cut from here and pasted at the bottom of the page.

KAB - Jan22 - Added two .cdx files to DropBox under "All BINAP-derived" and "All Organocatalysts", with all the summarised papers' catalysts. MHT - good idea.

KAB - Jan22 - (not sure of relevancy) Found "Stereoselectivity of Superacid-Catalyzed Pictet−Spengler Cyclization Reactions." 2003 Ohwada OrgLett (added to DropBox). Proposes dicationic intermediate/transition state(?) mechanism for PS reaction of non-activated aromatics in the presence of catalytic (achiral) acid. MHT - sounds interesting, will check it out.

KAB - Feb11 - Significant discussion of PS mechanism and acid-base effects on non-enzymatic aq solution PS reactions with enzyme cat. reactions, using kinetic isotope effects. RDS appears to be the same for both systems. Discusses pH dependence of enzyme for catalysis but not binding of substrate. Also, proposal of enzyme mechanism with key Glu309, where tryptamine is deprotonated, increasing its nucleophilicity for aldehyde attack. Not sure of how (or if) this is to be spread between mech vs enzyme section?

MAT - Feb11 - KAB, I'm trying to nail down more of the enzymatic "practical uses" in the Enzymatic Catalysis section, but I moved my comment about the OpSTS computation TS to your mechs section. I think, as Mat mentioned, that the catalysis section has to be for actual end-products, so I'll likely write up the NCS generation of benzoisoquinoline nps and O'Connor / Stockigt's work with fluorinated tryptamines for my section.

Specific Things That Need Doing

Introduction

• Need intro scheme containing structures for strychnine, morphine, vinblastine and reserpine and a scheme showing the synthesis of strictosidine from a PS reaction between tryptamine and secologanin. Combine with the existing structures of (-)-suaveoline and (-)-phalarine
• A number of small "needs" have been added to the intro section

'Quality Control

• Several "checks" still needed - essentially for accuracy of data and schemes, but stylistic points welcomed.

Papers that are relevant and need to be included for the first time

These papers are relevant and have not yet been included. They need a summary paragraph and possibly a scheme. Papers that are included need to have their citation data put in the right place in the review, and need to be added to the Mendeley Page. Papers that are not included should be listed in full in the "not-being used" section but do not need to be added to the Mendeley library.

• KAB: relevant. Early use of chiral phosphoric acids (binol and H8-binol) in enantioselective Morita-Baylis-Hillman reaction. N. T. McDougal, S. E. Schaus, J. Am. Chem. Soc. 2003, 125, 12094 (DOI: 10.1021/ja037705w) Paper MHT - that sounds very relevant - a year before Akiyama/Terada. Needs to be properly included? KAB Jan23 - Probably. It's a bit different to the rest. Acids were catalytic, but also required a "nucleophilic promotor." Not sure what that is, but it was present in less than stoich amounts as well.

Papers that have not yet been included, but have been referenced by others

These papers need to be checked for relevance. They typically have come from other, relevant papers, but the relevance may not be clear. If they are relevant and need including, move the citation from this section to the "needs to be included" section above. If you wish to then actually include it in the review, write "your initials - doing" next to the paper and start working.

Introduction/Background to the PS Reaction

Early examples: probably rac/achiral

• Nature: Naoi, M.; Maruyama, W.; Nagy, G. M. Neurotoxicology 2004, 25, 193- 204 (DOI: 10.1016/S0161-813X(03)00099-8) Paper

Some good medicinal chemistry examples of isatin-derived compounds in Franz 2011 and bencivennia 2011.

Check for the importance of the structural motifs constructed with the reaction:

• Brown, R. T. In Indoles; Saxton, J. E., Ed.; Wiley- Interscience: New York, 1983; Part 4 (The Monoterpenoid Indole Alkaloids)
• Bentley, K. W. Nat. Prod. Rep. 2004, 21, 395-424 and references therein
• W. Jiang, J. Guan, M. J. Macielag, S. Zhang, Y. Qiu, P. Kraft, S. (DOI: 10.1021/jm025545d) Paper

Example chiral auxiliary approach: H. Waldmann, G. Schmidt, H. Henke, and M. Burkard, Angew. Chem. Int. Ed Engl., 1995, 34, 2401. as an example of an "easily removable" chiral aux not being too different from a chiral reagent? Referenced by Nakagawa.

Also possibly: Bhattacharjee, T. M. John, D. Haynes-Johnson, S. Lundeen, Z. Sui, J. Med. Chem. 2005, 48, 2126 – 2133 (DOI: 10.1021/jm0401098) Paper

Specifically with respect to carbolines:

• Kawasaki, T.; Higuchi, K. Nat. Prod. Rep. 2005, 22, 761–793 (DOI: 10.1039/B502162F) Paper
• Yu, J.; Wang, T.; Liu, X.; Deschamps, J.; Anderson, J. F.; Liao, X.; Cook, J. M. J. Org. Chem. 2003, 68, 7565–7581 (DOI: 10.1021/jo030006h) Paper
• Liao, X.; Zhou, H.; Yu, J.; Cook, J. M. J. Org. Chem. 2006, 71, 8884–8890 (DOI: 10.1021/jo061652u) Paper
• Ma, J.; Yin, W.; Zhou, H.; Cook, J. M. Org. Lett. 2007, 9, 3491–3494 (DOI: 10.1021/ol071220l) Paper
• Herraiz, T. J. Chromatogr. A 2000, 881, 483–499 (DOI: 10.1016/S0021-9673(99)01313-8) Paper
• Herraiz, T.; Galisteo, J.; Chamorro, C. J. Agric. Food Chem. 2003, 51, 2168–2173. (DOI: 10.1021/jf0210066) Paper Could cite - carbolines show antioxidant activity.

Diastereoselective examples:

Early diastereoselective, to reference: Ungemach, F.; DiPierro, M.; Weber, R.; Cook, J. M. J. Org. Chem. 1981, 46, 164. (DOI: 10.1021/jo00314a035) Paper

Study to reference: Cox, E. D.; Hamaker, L. K.; Li, J.; Yu, P.; Czerwinski, K. M.; Deng, L.; Bennett, D. W.; Cook, J. M. J. Org. Chem. 1997, 62, 44-61 (DOI: 10.1021/jo951170a) Paper.

To Do:

• Czarnocki, Z.; MacLean, D. B.; Szarek, W. A. Can. J. Chem. 1986, 64, 2205-2210. (DOI: 10.1139/v86-363) Paper
• Czarnocki, Z.; Suh, D.; MacLean, D. B.; Hultin, P. G.; Szarek, W. A. Can. J. Chem. 1992, 70, 1555-1561. (DOI: 10.1139/v92-191) Paper
• Czarnocki, Z.; Mieckzkowsi, J. B.; Kiegiel, J.; Arazn ́y, Z. Tetrahyedron: Asymmetry 1995, 6, 2899-2902. (DOI: 10.1016/0957-4166(95)00380-0) Paper

Papers relating to indole chemistry in asymmetric catalysis, cited by Bencivennia 2011:

• M. Bandini, A. Eicholtzer, Angew. Chem. Int. Ed. 2009, 48, 9608–9644
• G. Bartoli, G. Bencivenni, R. Dalpozzo, Chem. Soc. Rev. 2010, 39, 4449 – 4465
• T. B. Poulsen, K. A. Jørgensen, Chem. Rev. 2008, 108, 2903 – 2915
• E. MarquØs-López, R. P. Herrera, M. Christmann, Nat. Prod. Rep. 2010, 27, 1138 – 1167

Diastereoselective cited by Leighton: C. Bohlmann, R. Bohlmann, E. G. Rivera, C. Vogel, M. D. Manandhar, E. Winterfeldt, Liebigs Ann. Chem. 1985, 1752 R. Amann, D. Spitzner, Angew. Chem. 1991, 103, 1373; Angew. Chem. Int. Ed. Engl. 1991, 30, 1320 D. L. Comins, M. M. Badawi, Tetrahedron Lett. 1991, 32, 2995 H. Wald- mann, G. Schmidt, M. Jansen, J. Geb, Tetrahedron Lett. 1993, 34, 5867 H. Waldmann, G. Schmidt, M. Jansen, J. Geb, Tetrahedron 1994, 50, 11865 H. Waldmann, G. Schmidt, H. Henke, M. Burkard, Angew. Chem. 1995, 107, 2608; Angew. Chem. Int. Ed. Engl. 1995, 34, 2402 T. Soe, T. Kawate, N. Fukui, T. Hino, M. Nakagawa, Heterocycles 1996, 42, 347 T. Kawate, M. Yamanaka, M. Nakagawa, Heterocycles 1999, 50, 1033

Diastereoelective Reactions

First examples?

• Ungemach, F.; Soerens, D.; Weber, R.; DiPierro, M.; Campos ;Mokry, P.; Cook, J. M.; Silverton, J. V. J. Am. Chem. Soc. 1980,102,6976.

Diastereoselective (note: must be catalytic for full inclusion - may be no examples):

• Czarnocki, Z.; MacLean, D. B.; Szarek, W. A. Can. J. Chem. 1986, 64, 2205-2210. (DOI: 10.1139/v86-363) Paper
• Czarnocki, Z.; Suh, D.; MacLean, D. B.; Hultin, P. G.; Szarek, W. A. Can. J. Chem. 1992, 70, 1555-1561. (DOI: 10.1139/v92-191) Paper
• Czarnocki, Z.; Mieckzkowsi, J. B.; Kiegiel, J.; Arazn ́y, Z. Tetrahyedron: Asymmetry 1995, 6, 2899-2902. (DOI: 10.1016/0957-4166(95)00380-0) Paper

Lewis Acids

This section is done

Bronsted Acid Section

Akiyama (2004) says these earlier reports "claim" the use of chiral B acids - is that the case, and is the work relevant here?

• KAB: Not relevant. Not chiral acid, use of chiral aux. in Diels-Alder. C. Palomo, M. Oiarbide, J. M. Garcia, A. Gonzalez, A. Lecumberri, A. Linden, J. Am. Chem. Soc. 2002, 124, 10288 (DOI: 10.1021/ja025906e) Paper
• KAB: relevant. Early use of chiral phosphoric acids (binol and H8-binol) in enantioselective Morita-Baylis-Hillman reaction. N. T. McDougal, S. E. Schaus, J. Am. Chem. Soc. 2003, 125, 12094 (DOI: 10.1021/ja037705w) Paper MHT - that sounds very relevant - a year before Akiyama/Terada. Needs to be properly included? KAB Jan23 - Probably. It's a bit different to the rest. Acids were catalytic, but also required a "nucleophilic promotor." Not sure what that is, but it was present in less than stoich amounts as well.
• KAB: not quite relevant. Uses H-bond activation via chiral TADDOL, in highly enantioselective Hetero-Diels-Alder. Y. Huang, A. K. Unni, A. N. Thadani, V. H. Rawal, Nature 2003, 424, 146. MHT - sure, but why is this paper in Nature? What is it showing that is so important, and does this need to be mentioned in the mech section?

Akiyama (2004) also mentions these "metal salt" versions:

• J. Inanaga, Y. Sugimoto, T. Hanamoto, New J. Chem. 1995, 19, 707 (KAB: Can't access on usyd subscription)
• KAB: Hetero-DA asymmetric amplification by chiral Yb complexes. H. Furuno, T. Hanamoto, Y. Sugimoto, J. Inanaga, Org. Lett. 2000, 2, 49 (DOI: 10.1021/ol991189q) Paper

Previous Bronsted acid example from Terada

• KAB: Not relevent. Chiral TADDOL used in hetero-DA reaction - Huang, Y.; Unni, A. K.; Thadani, A. N.; Rawal, V. H. Nature 2003, 424, 146.
• KAB: See above - McDougal, N. T.; Schaus, S. E. J. Am. Chem. Soc. 2003,125, 12094.

Example of chiral charged Brønsted acid catalyst:

• Nugent, B. M.; Yoder, R. A.; Johnston, J. N. J. Am. Chem. Soc. 2004,126, 3418.

Jacobsen Strecker and Mannich history, from Terada

• Sigman, M. S.; Jacobsen, E. N. J. Am. Chem. Soc. 1998, 120, 4901.
• Vachal, P.; Jacobsen, E. N. Org. Lett. 2000, 2, 867.
• Sigman, M. S.; Vachal, P.; Jacobsen, E. N. Angew. Chem., Int. Ed. 2000, 39, 1279.
• Su, J. T.; Vachal, P.; Jacobsen, E. N. AdV. Synth. Catal. 2001, 343, 197.
• Vachal, P.; Jacobsen, E. N. J. Am. Chem. Soc. 2002, 124, 10013.
• Wenzel, A. G.; Lalonde, M. P.; Jacobsen, E. N. Synlett 2003, 1919.
• Wenzel, A. G.; Jacobsen, E. N. J. Am. Chem. Soc. 2002, 124, 12964.

See also:

• Okino, T.; Hoashi, Y.; Takemoto, Y. J. Am. Chem. Soc. 2003, 125, 12672.
• Okino, T.; Nakamura, S.; Furukawa, T.; Takemoto,Y. Org. Lett. 2004, 6, 625.

Copper complex example from Terada:

• Marigo, M.; Kjærsgaard, A.; Juhl, K.; Gathergood, N.; Jørgensen, K. A. Chem.- Eur. J. 2003, 9, 2359.

The strengths of these chiral phosphoric acids is governed by:

• Akiyama Chem Rev 2007
• Terada ChemComm 2008

Reviews to check through for comments on mechanism of reactions and possible applications of Bronsted acids that have not yet been applied to the PS.

• S.J. Connon, Angew. Chem. Int. Ed. 2006, 45, 3909–3912
• T. Akiyama, J. Itoh, K. Fuchibe, Adv. Synth. Catal. 2006, 348, 999 – 1010
• M. S. Taylor, E. N. Jacobsen, Angew. Chem. Int. Ed. 2006, 45, 1520–1543
• Connon, S. J. Org. Biomol. Chem. 2007, 5, 3407–3417
• Terada Synthesis 2010, 1929-1982
• List, Top. Curr. Chem. 2010, 291, 395-456
• Rueping Angewandte 2011, 50, 6706-6720
• S.-L. You, Q. Cai, M. Zeng, Chem. Soc. Rev. 2009, 38, 2190 – 2201
• A. Zamfir, S. Schenker, M. Freund, S. B. Tsogoeva, Org. Biomol. Chem. 2010, 8, 5262 – 5276 (DOI: 10.1039/c0ob00209g)

Bronsted Acids: N-triflyl phosphoramide Yamamoto 2006, N-triflyl phosphoramide [10.1002/anie.200802139 Rueping 2008] , ? Rueping 2010
Diastereoselective polycyclization involving unactivated Ph using SnCl₄ Yamamoto 2006 - suggestion here to use this enantioselectively.

Link from PS page - MNR

Nakamura 2009 - but Aza-Friedel-Crafts Alkylation of Pyrroles
Possible alternative thiophosphoramide: Yamamoto 2008

Organocatalysis Section

Check for relevancy:

• Metal-free organocatalysis through explicit hydrogen bonding interactions, Schreiner, P. R. Chem. Soc. ReV. 2003, 32, 289. (DOI:10.1039/b107298) - KAB: Not B Acids. On Thio-Urea.
• (Thio)urea organocatalysis—What can be learnt from anion recognition?, Z. Zhang, P. Schreiner, Chem. Soc. Rev. 2009, 38, 1187 – 1198 (DOI: 10.1039/B801793J) Paper - KAB: Not on B acids. Thio-urea stuff.

Not looked at to see which section these go in:

• Asymmetric Bronsted Acid Catalyzed Nucleophilic Addition to in situ Generated Chiral N-Acyliminium Ions, Rueping, M.; Nachtsheim, B. J. Synlett 2010, 1, 119. (DOI: 10.1055/s-0029-1218539) - KAB: Probably needs to go in the B acid section.
• Peterson, E. A.; Jacobsen, E. N. Angew. Chem., Int. Ed. 2009, 48, 6328.
• Raheem, I. T.; Thiara, P. S.; Jacobsen, E. N. Org. Lett. 2008, 10, 1577
• Sun, F.-L.; Zheng, X.-J.; Gu, Q.; He, Q.-L.; You, S.-L. Eur. J. Org. Chem. 2010, 47

Link taken from PS page - MNR

Cationic Polycyclizations Jacobsen 2010

Mechanism section

Some possibly relevant papers arising from Dixon 2010, on chiral counterion-induced enantioselective N-acyliminium ion reactions:

• Li, G.; Kaplan, M. J.; Wojtas, L.; Antilla, J. C. Org. Lett. 2010, 12, 1960.
• Terada, M.; Machioka, K.; Sorimachi, K. Angew. Chem., Int. Ed. 2009, 48, 2553.
• Rueping, M.; Lin, M.-Y. Chem.sEur. J. 2010, 16, 4169.

Some papers on dual catalysis referenced by Franz 2011:

• Yamamoto, H.; Futatsugi, K. Angew. Chem., Int. Ed. 2005, 44, 1924–1942
• Lv, J.; Li, X.; Zhong, L.; Luo, S.; Cheng, J.-P. Org. Lett. 2010, 12, 1096–1099
• Rueping, M.; Koenigs, R. M.; Atodiresei, I. Chem. Eur. J. 2010, 16, 9350–9365.

The general reviews need to be checked, to ensure we have not missed anything, and as inspiration for thoughts on the reaction mechanism. e.g. Govindra Org Reactions review we've already cited.

Enzymatic Section

On the promiscuity of the enzyme norcoclaurine synthase: Biocatalytic Production of Tetrahydroisoquinolines, B. M. Ruff, S. Bräse and S. E. O’Connor, Tetrahedron Lett. 2012, 53, 1071-1074 Paper and

• Biocatalytic asymmetric formation of tetrahydro-beta-carbolines, Bernhardt Peter; Usera Aimee R.; O'Connor Sarah E., TETRAHEDRON LETTERS 2010, 51, 4400-4402 paper - already cited, but make sure it's covered.

Other Relevant Systems not yet applied to the PS

Check these papers for possible suitability for the PS, and check that they have not been so-used. The aim is to say in the review which catalysts show promise but are unexplored.

Strong Bronsted acids not yet applied to PS:

• Chiral N-triflyl phosphoramide Yamamoto 2006

Check:

• C. H. Cheon, H. Yamamoto, J. Am. Chem. Soc. 2008, 130, 9246–9247 (DOI: 10.1021/ja8041542) Paper
  
• C. H. Cheon, H. Yamamoto, Org. Lett. 2010, 12, 2476–2479 (DOI: 10.1021/ol100233t) Paper
  
• M. Rueping, W. Ieawsuwan, A. P. Antonchick, B. J. Nacht- sheim, Angew. Chem. Int. Ed. 2007, 46, 2097–2100 (DOI: 10.1002/anie.200604809) Paper
  
• P. Jiao, D. Nakashima, H. Yamamoto, Angew. Chem. Int. Ed. 2008, 47, 2411–2413 (DOI: 10.1002/anie.200705314) Paper
  
• H. Xu, S. J. Zuend, M. G. Woll, Y. Tao, E. N. Jacobsen, Science 2010, 327, 986–990 (mixture).
  
• M. Treskow, J. Neudörfl, R. Giernoth, Eur. J. Org. Chem. 2009, 3693–3697.
  
• P. García-García, F. Lay, P. García-García, C. Rabalakos, B. List, Angew. Chem. Int. Ed. 2009, 48, 4363–4366.
  

TADDOL ligands:

• Akiyama 2005
• (TADDOL activator) Rawal 2003

Enzymatic examples: (Working on, MAT)

• Norcoclaurine synthase Tanner 2007
  
• Strictosidine Synthase Stoeckigt 2008
  
• Deacetylipecoside Synthase - need ref if this is a relevant enzyme

Lewis Acid Examples that seem to be Relevant:

• Tang 2009

Miscellaneous, not 100% relevant:
Asymmetric prolinol Michael addition followed by diastereoselective PS - Fisher 2009
Ditto - Zhao 2010

• Trifluoroacetic Acid-Promoted Synthesis of 3-Hydroxy, 3-Amino and Spirooxindoles from alpha-Keto-N-Anilides, Gorokhovik Ioulia; Neuville Luc; Zhu Jieping, ORGANIC LETTERS, 2011, 13, 5536-5539 paper - not PS, but similar ketoamide substrates vs Leighton, and similar reactivity pattern. Not asymmetric.

Papers that may use the cat, asymm PS in syntheses, to be checked

MAT - Jan 30 - Per Sanjay's request, a Reaxys search for "asymmetric Pictet-Spengler" returns 110 hits, and "catalytic asymmetric Pictet-Spengler" returns only 9. In the former, several recent syntheses we haven't yet addressed (saframycin, alstoscholarine, polyneuridine) may need to be checked to see if they incorporate catalytic methodology to set stereochem (currently looking through syntheses - MAT Feb 11)

Simple items to do

• MHT - Jan21 - Need people to go through all the references on this page and insert a DOI link for ease of access.
  

Quality Control

All papers included in the main text of the review will have been summarised by one person. The summary (text and scheme) need to be checked by at least one other person - that means going back to the primary literature source. This section contains a list of who has done what.

Arrange list in approximate order of appearance in review.

• Nakagawa 1998 (10.1021/jo980810h) - written by MNR, checked and rewritten by MAT, checked by KAB - Scheme needs recheck.
  
• Leighton 2009 (10.1002/anie.200806110) - written by MNR - checked by MHT - rechecked by KAB.
  
• Akiyama (10.1002/anie.200353240) - written by MHT, checked and rewritten by MAT - needs recheck.
  
• Terada (10.1021/ja0491533) - written by MHT, checked by MAT.
  
• List 2006 (10.1021/ja057444l) - written by MHT, not yet checked.
  
• Hiemstra 2007 (10.1002/anie.200701808) - written by KAB, checked by MNR & MHT.
  
• Hiemstra 2008 (10.1021/jo8010478) - written by KAB, checked by MNR & MHT.
  
• Hiemstra 2009 (10.1021/ol900888e) - written by MHT, checked by KAB - needs further check
  
• Hiemstra 2011 (10.1021/jo201657n) - written by MHT, not yet checked.
  
• Dixon 2009 (10.1021/ja9024885) - written by MHT, not yet checked.
  
• Dixon 2010 (10.1021/ol101651t) - written by KAB, checked and rewritten by MHT - needs further check.
  
• Franz 2011 (10.1016/j.tetlet.2011.08.071) - written by MNR, significantly re-worked by MHT - needs further check.
  
• Tian 2011 - Writing in progress KAB
• Jacobsen 2004 - written by MNR, checked and rewritten by MAT - needs recheck.
  
• Jacobsen 2007 - written by MNR, not yet checked.
  
• Jacobsen 2007 review - written by MNR, not yet checked.
  
• Jacobsen 2008 - written by MNR, checked by KAB - needs further check.
  
• Jacobsen 2009 - written by MNR, KAB currently working on.
  
• Jacobsen 2011 - written by MNR, checked and rewritten by MAT - needs recheck.
  
• O'Connor 2008 / 2010 - written by MAT, not yet checked.
  
• Stockigt 2012 - written by MAT, not yet checked.
  

Resolved

• KAB - Jan21 - The scheme for 2009 Hiemstra with the H8-BINOL phosphoric acid in the box, doesn't have the H8-BINOL phosphoric acid in the box. Still has the BINOL. (KAB: fixed in the chemdraw file and re-uploaded the png, but it is yet show the change in the review.) - KAB, done.

• 1. KAB attempt to understand 2000 Koomen OrgLett The figure for Table 1 gives diasteromeric ratios. Where are the diastereomers? I only the possibility for enantiomers in the product. Where's the other stereogenic centre? They also mentioned "hydrolysis of the starting material" numerous times. I'm assuming they mean hydrolysis of the N-S bond (there doesn't seem any other reasonable place for hydrolysis of the SM to occur), but I just wanted to check. This comment resolved since this paper no longer included in the review.

• MHT - Jan 22 - Reworked Dixon 2010 into one scheme. KAB please check and comment. KAB: Neater. Is the formation of the enamide intermediates reversible? I was under the impression the first condensation was irreversible. So forego the "best" result, in terms of ee and yield and instead incorporate the mech into the scheme? MHT: I doubt enamide formation is reversible (in its entirety) but it's a toluene reflux, so might be worth erring on the side of caution. And yes - I have foregone the "best" result here so we can combine mechanism and reaction outcome in one. Typical yield/ee mentioned in text.

• MHT - Jan21 - Do we have a significant section on enzyme examples, or do we refer to the 2011 Waldmann review, which appears to cover this well? I would favour a brief description, with the value being clues we learn about the mechanism of catalysis, and whether we can apply those lessons to small molecule catalysis. Resolved because enzyme section now included, with emphasis on preparative utility and, in a separate section, an emphasis on what we learn about the mechanisms of the enzyme-catalyzed reactions.

• MAT - Jan 29 - Can someone tell me how to be added to the review DropBox? I have the program installed, but I can't seem to access the folder. (Mendeley works just fine, btw) Resolved - Murray has added Mike to the shared "Pictet-Spengler Review" folder

• MAT - Feb 11 - Natural product synthesis - hongconin and thysanone use Oxa-Pictet-Spengler, non-catalytic. Do not include.

• MAT - Feb11 - Can someone grab the Nature 2010, p.461 O'Connor paper and place it in Dropbox? It's crucial for the enzyme section (no easy access to Nature here!) KAB Added to dropbox

• KAB - Jan22 - Need to annotate Dixon 2010 Cyclisation Cascade with keq's and kminor and kmajor - but MHT has altered this scheme, and I don't think the k's add anything.

• MAT / KAB / MHT - Feb 12 - For anyone who wants to answer, the graphics all have to be open-sourced, right? So I can't clip a xstal structure out of a paper and re-use it here, even if I attribute it to JACS? Please clarify. (KAB reply): are you able to access the PDB, manipulate then export using Jmol? I'm guessing it's enzyme related. (MAT reply): I was going to .pdf snapshot the enzyme overlay from O'Connor JACS 2008 (with the pink and green substrates) to use here, but I likely have to request permission to do so. MHT - correct, we'd need to seek permission. That makes things more complex, so better to do things ourselves using public data, but we can go the permission route if that generates the best drawing. (KAB reply): Yes. I've just downloaded the PDB file with the inhibitor (green) in the binding site. It's available from http://www.rcsb.org/pdb/explore/explore.do?structureId=2VAQ. Interesting. Dimer with 2 active site. And in complex with substrate (I'm guessing that's the pink one?) http://www.rcsb.org/pdb/explore.do?structureId=2V91. It's easy enough to manipulate the PDB to our liking. Can even do our own overlays. Bonus that Jmol is open source. Resolved - we can make our own enzyme overlays from PDB files

• MAT/MHT - MAT - Feb13 - How are we calibrating use of the word "high?" (to describe yield or ee). We have >20 examples of its usage in the review thus far, and seems to encompass a wide range of numbers (70s to 99%!). Resolved with comment above about terminology

• KAB - Mar 3 - RE: Nakagawa 1998. The paper states the reaction is the first example of "reagent-controlled asym. PS reaction." What does that mean? (MHT - means that the thing guiding the stereochemical outcome is something that is added to the reaction mixture but doesn't become part of the product. This distinguishes it from diastereoselective examples where the stereochemistry is defined by a stereocentre already in the molecule, as with many of Cook's examples. However, it's not always completely clear cut. Waldmann used an "easily removeable" chiral aux, which is not so different from a strongly-attached Lewis Acid) Also, first report was in preliminary communication in 1996. So, first reported in 1996 or 1998? MHT - Yes, looks like this needs to be checked T. Kawate, H. Yamada, T. Soe and M. Nakagawa, Tetrahedron: Asymmetry 1996, 7, 1249-1252 Paper Resolved

• Nakagawa first example of reagent-controlled PS? MHT: I think it is - need that confirmed. MAT: - Yup, The Hino 1992 Heterocycles work was all spirocycles, and the 1996 Tet Asymm was what I wanted included. It's AOK now. Resolved
  

• Kat - please check the facts and the new scheme for accuracy (original had a mistake in the borane structure).- KAB 17 Mar: Facts are good. As for the scheme, the "left" ipc is correct, but I'm not 100% sure about the right one.Done!
  

• Lews Acid Section: Pictet-Spengler Reactions of Nb-Hydroxytryptamines and Their Application to the Synthesis of Eudistomins, T. Hino and M. Nakagawa, Heterocycles 1998, 49, 499-531 Paper. Abstract from WoS reads: "Methods for preparing Nb-hydroxytryptamines, their Pictet-Spengler reactions with various aldehydes via nitrones, and their asymmetric inductions are reviewed. Syntheses of oxathiazepine-containing eudistomins and related natural products which incorporate these reactions are also reviewed". This may need to be referenced in Nakagawa's work on Lewis Acid-mediated asymmetric PS. MHT has ordered from Sydney Library 16 Jun 2012. Received June 19 and put in Dropbox. MHT Oct 20th - Included as ref - no obviously new data not covered by research articles - this is more of a review. Resolved