Total Synthesis of All (-)-Agelastatin Alkaloids Mohammad Movassaghi, Dustin S. Siegel and Sunkyu Han MIT Chemical Science, Advance article N NH Br O OMe NH N O Me Bioinspired cyclization N NH NH N Br O O Me H HO H H (-)-Agelastatin A (+)-O-Me-pre-agelastatin A 1.4 g batch Marija Manojlović Wipf group current literature meeting 8-27-2010
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Total Synthesis of All (-)-Agelastatin Alkaloids
Mohammad Movassaghi, Dustin S. Siegel and Sunkyu Han
MIT Chemical Science, Advance article
NNH
Br
O
OMe
NHN
OMe
Bioinspired cyclization N
NH
NH
NBr
O
OMe
H
HO
H
H
(-)-Agelastatin A(+)-O-Me-pre-agelastatin A
1.4 g batch
Marija Manojlović Wipf group current literature meeting
8-27-2010
Agelastatin alkaloids • 6 Agelastatins A-F isolated so far, differences in substitution pattern
• Agelastatin A biological activity: – Singnificant antitumor activity against wide range of tumor cells (in nM range) – Highly toxic towords anthropods (LC50= 1.7 ppm in brine shrimp assay) – Insecticidal against beet army worm and corn root worm – Selectivly inhibits the glycogen synthase kinase-3b, a potential target for the treatment of
Alzheimer’s disease and bipolar disorder.
• Biosynthetically originate from simpler pyrrole-imidazole alkaloids
NNH
NH
NBr
O
OMe
H
HO
H
H
Agelastatin A
NNH
NH
NBr
O
OMe
H
HO
H
H
Agelastatin B
Br NNH
NH
NBr
O
OMe
OH
HO
H
H
Agelastatin C
NNH
NH
NBr
O
OH
H
HO
H
H
Agelastatin D
NNH
NH
NBr
O
OMe
H
MeO
H
H
Agelastatin E
NNH
NH
NBr
O
OH
H
HO
H
H
Agelastatin F
Br
Pietra et al. J. Chem. Soc., Chem. Commun. 1993, 1305.
Molinski et al. J. Nat. Prod. 1998, 61, 158. Al-Mourabit et al. J. Nat. Prod. 2010, 73, 720.
Movasaghi, Siegel and Han, Chem. Sci. Advance article. Trost and Dong, CEJ 2009, 15, 6910.
N
HN
NH2X = Y = H clathrodinX = H, Y = Br hymenidinX = Y = Br oroidin
NH
O
NHY
X
Previous synthetic work: Agelastatin A - benchmark for showcasing methodology
• 10 total syntheses published prior to the title paper • First synthesis: Weinreb 1999, first asymmetric synthesis: Feldman 2002.
• In all previous synthesis cyclopentane ring C is set early and the rest of molecule is elaborated around it
• Ring C contains 4 stereocenters and this highly substituted cyclopentane was target for showcasing various methodologies.
Weinreb: JOC 1998, 63, 7594 and JACS 1999, 121, 9574. Feldman: JACS 2002, 124, 9060 and JOC 2002, 67, 7096. Hale: OL 2003, 5, 2927 and OL 2004, 6, 2615. Davis: OL 2005, 7, 621 and SC 2009, 39, 1914 (CL in Feb. 2005 by Mike Rishel). Trost: JACS 2006, 128, 6054 and CEJ 2009, 15, 6910. Ichikawa: OL 2007, 9, 2989. Wardrop: OL 2009, 11, 1341. Chida: OL 2009, 11, 2687. Tanaka: OL 2008, 10, 5457 and OL 2009, 11, 3402. Du Bois: ACIE 2009, 48, 3802 (CL in May 2009 by Melissa).
- The first total synthesis of agelastatin A - Key steps: hetero DA reaction, Sharpless-Kresze allylic amination (new SES reagent) and internal Michael addition of pyrrole nitrogen - Why not brominate debromoagelastatin, previously made in Weinreb group?
JOC 1998, 63, 7594. JACS 1999, 121, 9574.
Feldman’s Synthesis of (-)-Agelastatins A and B
- The first enantioselective total synthesis of (-)-agelastatin A - Cyclopentane core was synthesized using alkylnyliodonium salt mediated cyclization
- New methodologies such as Pd-catalyzed asymetric allylic alkylation (AAA) using pyrrole as nucleophile and In(OTf)3 catalyzed oxidative aziridine opening using DMSO were developed. - Both enantiomers of Agelastatin A were synthesized from the same enantiomer of a stereoconducting catalyst.
JACS 2006, 128, 6054. Chem. Eur. J. 2009, 15, 6910.
Biosynthesys of Oroidin-Based Pyrrole-Imidazole Alkaloids
Ali Al Mourabit and Pierre Potier Eur. J. Org. Chem. 2001, 237.
HN
N
NH2
CO2H
histidineHN CO2H
proline
HN
NH2N NH2
HN CO2HBr
NH
HN
NHNH
O
NH
Br
oxidation
N
NNH
NH
O
NH
Br
H+
H
O
NH
Br
NH
NH
NNH
H+
O
N
Br
NH
NH
NHNH
O
N
Br
NH
NH
NNH
hydrationmethylationhydrolysis
NNH
NH
NBr
O
OMe
H
HO
H
H
X = H Agelastatin AX = Br Agelastatin B
Nu: E+
XX X
X X
X
X
48
Title Paper: Biosynthetic Hypothesis and Design Plan for Total Synthesis of Agelastatins
Title Paper: Synthesis of (-)-Agelastatin A
H2N CO2Me
CO2Me
N CO2Me
CO2MeNBS, DTBMP
THF, 92% N CO2Me
CO2MeBr
OMeOOMe
ClCl
H2O, 80 °C, 2 h84% 99% ee
ClSO2NCOMeCN, 0 °C;
Na(Hg), NaH2PO482%
N CO2Me
CO2MeBr
O
H2N
NaBH4, MeOH, 0 °C,TsOH·H2O, rt, 90%
NNH
Br OMe
O
O
O
NNH
Br OMe
O
O
OMe
> 99% ee> 10g scale
> 20g scale
TolSH, AlMe3CH2Cl2, 0 °C, 92%
NNH
Br STol
O
O
OMe
Cy3Sn NH
NH
OMe CuTC, THF
50 °C; HClMeOH, 58%
NNH
Br
O
OMe
NHN
OMe
N NNTol
MeOCy3Sn
CuTC, THF50 °C, 96%> 5g scale
NNH
Br
O
O
OMe
N N
N
MeO
Tol
HCl, MeOH65 °C, 89%
NNH
Br
O
O
OMe
HN
HN Me
O
MeSO3H, H2O, 100 °Cthen MeOH, 71%
NNH
NH
NBr
O
OMe
H
HO
H
H
(-)-Agelastatin A
> 1g scale+NNH
NH
NBr
O
OMe
H
MeO
H
H
(-)-O-Me-di-epi-agelastatin A
1 : 2
MeSO3H, H2O, 100 °Cthen MeOH, 66%
The Importance of C13 Bromine Substituent and Imidazolinone
NNH
Br OMe
O
O
O
NNH
Br OMe
O
O
OMe
> 99% ee
N CO2Me
CO2MeBr
O
H2N
NaBH4, MeOH, 0 °C,TsOH·H2O, rt, 90% 77
13 13
No epimerization at C7
CD3OD, 2 hN
NH
Br OMe
O
O
O
713
D
99%racemic
N CO2Me
CO2MeH
O
H2N
NaBH4, MeOH, 0 °C,TsOH·H2O, rt, 90%7
13 NNH
H OMe
O
O
OMe
Significant epimerization at C7
NNH
H
O
OMe
NHN
OMe
MeSO3H, H2O,100 °C, 20 min, 57%
NNH
H
O
NHN
OMe
NNH
Br
O
OMe
NN
NH2H
Dowex, H2O100 °C, 92%
NNH
Br
O
NN
NH2H
Title Paper: Synthesis of (-)-Agelastatins B-F
NNH
NH
NBr
O
OMe
H
HO
H
H
(-)-Agelastatin A
NBS, DTBMPTHF, H2O, 0 °C
84%N
NH
NH
NBr
O
OMe
H
HO
H
H
(-)-Agelastatin B
Br
Amberlyst 15MeOH, 65 °C
96%N
NH
NH
NBr
O
OMe
H
MeO
H
H
(-)-Agelastatin E
NNH
NH
NBr
O
OMe
H
MeO
H
H
(-)-O-Me-di-epi-agelastatin A
pyr, 115 °C
99%N
NH
NH
NBr
O
OMe
H
H
DMDO, acetoneH2O, 98%
NNH
NH
NBr
O
OMe
OH
HO
H
H
Amberlyst 15H2O, 100 °C
5 d, 41% NNH
N
NBr
O
OMe
H
HH N
NH
NH
NBr
O
OMe
OH
HO
H
H
(-)-Agelastatin C
NNH
Br STol
O
O
OMeCy3Sn N
HNH2
O1. CuTC, THF, 50 °C;
2. HCl, MeOH62%
NNH
Br
O
OMe
NHHN
O
MeSO3H, H2O100 °C;
HCl, MeOHN
N
Br
O
NHHN
O
H
NNH
NH
NBr
O
OH
H
HO
H
H
(-)-Agelastatin D26%
+ NNH
NH
NBr
O
OH
H
MeO
H
H
9%
NN
Br
O
NHHN
O
H
NHN
HN
HN
O
O
H
HNHN
O
Br
20%
20%
NNH
NH
NBr
O
OH
H
HO
H
H
(-)-Agelastatin D
NNH
NH
NBr
O
OH
H
HO
H
H
(-)-Agelastatin F
Br
NBS, DTBMPTHF, H2O, 0 °C
86%
Conclusions • All known agelastatin alkaloids were synthesized employing
biosynthetically inspired strategy
• “Pre-agelastatin” derivatives were obtained in multi-gram quantities
• C13 bromine substitution was critical for the successful C-ring cyclization
• Agelastatin A was prepared in 1.4 g batch and bilogical and chemical studies of that compound are ongoing.
• Authors suggest higher probability for biosynthetic introduction of C13-bromopyrrole and imidazolone substructures prior to C-ring formation and this hypothesis is yet to be experimentally checked.