a research project in the second semester organic chemistry laboratory
DESCRIPTION
A Research Project in the Second Semester Organic Chemistry Laboratory. Timm A. Knoerzer Nazareth College NERM 2004 Rochester, NY. The Problem. Students are usually not engaged in problem solving or critical thinking while in the laboratory - PowerPoint PPT PresentationTRANSCRIPT
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A Research Project in the Second Semester Organic Chemistry Laboratory
Timm A. Knoerzer
Nazareth College
NERM 2004
Rochester, NY
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The Problem Students are usually not engaged in problem
solving or critical thinking while in the laboratory No connection of work from week to week (does
not simulate the real world; the “one and done” scenario)
Chemistry not done in context (scientifically relevant)
Student do not always learn about modern chemical techniques and reactions
Limited integration of technology Little exposure to structurally sophisticated
molecules
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The Objectives
Do what real organic chemists do (perform a multi-step, multi-week project that requires students to plan, adapt, modify, improvise)
Learn modern/advanced chemical techniques Use technology to support and explain
experimental outcomes Learn relevant chemistry (connected to what
students are learning in class and are interested in) Summarize and communicate the work (report and
poster)
Provide students with an opportunity to:
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Synopsis of The Project Objective: To generate a diverse small molecule
library of benzothiazine/amino acid/isothiocyanate hybrids
Context: Students are active participants in generating new compounds and in rehearsing critical synthetic transformations
Novelty: Synthesize a heterocycle that has limited precedence in the chemical literature (unknown utility)
Relevance: To ultimately explore the binding potential of these compounds toward various molecular recognition targets (receptors, enzymes, and other proteins) = bioorganic chemistry
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Synopsis of The Project
Strategy: Combinatorial chemistry in conjunction with the synthesis of key nitrocinnamic acid starting materials
Schedule: Spring semester -- Begins in week 5; ends in week 14 (total of 9 weeks)
Topics: carbonyl addition, NAcS, SN2 (Mitsunobu), peptide synthesis, NArS, synthesis of ethers, enolates, use of protecting groups, spectroscopy, molecular modeling, scientific communication – parallels the chemistry introduced in class
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Our target
H2N NH
O HN
R1 O NS
HN
R2
R3
linker
diversification #1: amino acids
diversification #2: nitrocinnamic acids
diversification #3: phenyl isothiocyanates
**
R4
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Combinatorial strategy
OH
AA1
AA2
AA3
attach linker split #1NCA1
NCA2
split #2I1
I2
SCN1
SCN2
I3split #3
T1
Total AA = 3, total NCA = 2, total SCN = 2
3 x 2 x 2 = 12 total compounds in this library
Solid-phase parallel synthesis
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Synthesis
OHH2N NH2
N N
O
N N
(CDI)
O NH
O
NH2HO
ONH
R1
O
O
HOBt, HBTU, Hunig's base
DMFWang Resin (1.1mmol/gram)
O NH
O
NH
O HN
R1
fmoc20% piperidine
DMF
HO
O
O2NR2
R3
DCC, HOBt, Et3N
DMF
O NH
O
NH
OHN
R1 O NO2
R2
R3
DMF
SnCl2
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Synthesis
O NH
O
NH
OHN
R1 O NH2
R2
R3NCS
DMF
R
H2N NH
O HN
R1 O NS
HN
R2
R3
R4
O NH
O
NH
O HN
R1 O NH
R2
R3
S
HN
50% TFA, CH2Cl2
R4
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Nitrocinnamic Acid Synthesis
H
O
H3CO
H3CO NO2
HH3CO
H3CO NO2
OO
HO2C CO2H
HHO
H3CO NO2
OOH
RO
H3CO NO2
OO
HO OH
R OH
HRO
H3CO NO2
ORO
H3CO NO2
O
OH
pTSA, toluene
20% aq. KOH
dioxanereflux reflux
10% aq. HCl
piperidine, pyridine
PPh3, DIAD
acetone, heat
We have used this scheme to construct 13 novel substituted 2-nitrocinnamic acidsMcDonald, E; Suksamrarn, A. J. Chem. Soc., Perkin Trans. 1 1978, 440-446.
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Project Design PowerPoint introduction to project Students select synthetic units:
(2-3) amino acids (2) nitrocinnamic acids (1-2) phenyl isothiocyanates may also select linker
Students are responsible for generating enough synthetic material to complete project (need ~20 mg of the final compound)
Students are responsible for using analytical and spectroscopic methods to confirm products
Students must decide if synthetic products are pure enough to continue – if not they must purify (e.g. chromatography)
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Technology Connection #1
HH3CO
H3CO NO2
OO
HHO
H3CO NO2
OO20% aq. KOH
dioxanereflux
1. Is this pathway SN2 or NArS?2. Why does the conversion occur para to the nitro group
rather than meta upon exposure of the starting 4,5-dimethoxy compound to 20% KOH (aq)?
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Molecular Modeling (Spartan)The red line represents the energy of the transition state (kcal/mol) and the green line represents the charge on the incoming OH nucleophile.
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More Modeling ResultsHere surface value = +20 in range of –60 to +26
Here surface value = +13 in range of –60 to +26
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Technology Connection #2
How can you confirm the identity/purity of your products?
NMR
Mass Spec LC
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Example NMR data
1.00 1.23
0.99
5.60
2.95
1.92
2.23
3.19
8 7 6 5 4 3 2 1 ppm
O
O
O
O NO2
CH3
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NMR Expansions
2.0 1.8 1.6 1.4 1.2 1.0 ppm
4.3 4.2 4.1 4.0 3.9 3.8 3.7 3.6 ppm
O
O
O
O NO2
CH3
a
b
b
c
d
e
f
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Example Mass Spec and LC data
H2N NH
OHN
O NH2
O
OMe
H2N
M+1 at 478.4 amu
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More Mass Spec and LC data
H2N NH
OHN
O N
H2N
S
HNPh
M+1 at 483.2 amu
“391” = loss of NH-Ph“348” = leftover starting material (incomplete rxn)
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Further Study and Extensions Design TLC system to monitor the course of
the Mitsunobu reaction and to perform subsequent column chromatographic purification
Determine how to obtain solid products that are free of solvent
Further confirmation of products by 13C-NMR, 13C-DEPT, and 1H-1H-COSY
Adjust # of equivalents and observe changes MECHANISMS Must determine how much analysis is to be
completed for “publication”
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Communicating results
Poster
Formal Report
Questions to Ponder
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Pictures
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Pictures
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Acknowledgements
Dr. Benjamin Miller (U of R Medical School Center for Future Health)
Dr. Paula Satterly-Childs Nazareth College summer research students
(Jessica Goodman, Jennifer Cahoon, Christina Gallis, Ed O’Neil, Ashanti Tolbert)
Graduate students in the the Miller group Terry O’Connell Organic chemistry students 2002-2004