douglas amato, thesis.pptx

7/28/2019 Douglas Amato, Thesis.pptx

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Douglas Amato

Latent Cysteine Residues on

Polymers prepared via Freeand Controlled Radical

Polymerizations


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Part ILatent cysteine residues formed via RAFT

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Goals of Click Chemistry

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Quantitative yields

Tolerant to functional groups

Insensitive to solvents

Example:

Copper mediated azide alkyne cycloaddition

R+ R'

N3Cu(I) N

NN

R

R'


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Development of New Click Rxns

Variety of Click reactions currently exist

Diels-Alder (DA)

Thiol-ene/yne (TE/TY)

Oxime

Limitations

Require an external stimulus (DA & TE/TY)

Require additional reagents (TE/TY)

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Goal - Develop Click chemistry that is biocompatible, non-

reversible, and does not require an external stimulus to add

new functionality to existing materials


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Thiazolidine linkages

Reaction is simple

No external stimulus or additional reagents

Not thermally reversible

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Example of thiazolidine linkages

Grinstaff lab at BostonUniversity

Utilized as suturingmaterial in eyesurgery

Challenging sythesis

Limited through-put

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Reversible AdditionFragmentation Chain

Transfer (RAFT) Polymerization

Predetermined Mn

Low PDI

Able to prepare block copolymers

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RAFT

Wide range of monomers Terminated with transfer agent

Can reduce transfer agent to thiol functionality

Part of thiazolidine linkage

Need amine functionality8


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Thiazolidine Prepolymer

Prepare a styrene-block-acrylonitrile copolymer

Reduce to form a cysteine like functionality

Only need/want a few AN repeat units

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Polymer Synthesis

Simple and efficient synthesis

Able to prepare large quantities of material

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Step-Wise Reduction Method

Reduce and prepare disulfide to prevent coupling

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Coupling Experiments

Clean shift in GPC indicates simple and effective coupling12


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Limitations and Solutions

LAH : effective but incompatible with other functional groups

Use tetrabutylammonium borohydride (TBABH4)

New transfer agents Prepare easy to synthesize RAFT transfer agents

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New Transfer Agents

Simple and efficient synthesis

Able to polymerize styrenes and acrylates

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TA:1 Polymer Synthesis

Modification of previously established method New AN extension conditions

15Conditions : A) TA-1, RAFT; B) AN, RAFT; C) MTS, propyl amine;D) i TBABH4, THF, EtOH ii - DTT, isophthaldehyde


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Polystyrene

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PS-PAN

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PS-PAN-S-S-CH3

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Coupling

TA-1 and TA-3 showed best coupling, but not nearideal.

TA-1 used for optimization due ease of synthesis

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Potential Issues

Solvent

Reaction time

Dithiothreitol

Basic solution

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Solvent / Reaction Time

More polar= higher coupling

Time for thiazolidine ring formation insignificant

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Dithiothreitol

More DTT = higher coupling efficiency

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Potassium Carbonate

More K2CO3= Increase in coupling

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Conclusions / Future Work

Trithiocarbonates unable to achieve 100 % coupling

Coupling conditions were attempted to be optimized Dependent upon : [K2CO3],[DTT],solvent

New goal: synthesis of a single molecule that containscysteine residue to attach to polymer

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Part IILatent small molecule cysteine residues


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Goals

1. Design a molecule that contains a latent(i.e. protected) cysteine residue

2. Incorporate molecule into a polymer

3. Prove exposure of cysteine residues

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Initial synthetic scheme

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Synthesis of mesylated compound successful.

However required column to purify


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Mesylate to thioacetate

Showed multiple spots via TLC

Alternative route investigated

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New Approach

Start with cysteine and add protectinggroups

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Thia


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1H NMR

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a

a

b

b

c

c

d

d

Thia


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Next step

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Forma-thia


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1H NMR

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thia

Forma thia


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Alkylation of carboxyl group

Ester proved unstable in acid

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Solution

Use acid stable linkage such as amides

Various carbodiimides did not prove to beeffective

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Alternative to carbodiimide coupling

Mixed anhydride

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Proof of amide formation

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formathia


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Incorporation into Polymeric System

Need to synthesize polymerizable amines.

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Routes

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Synthesis of 4-vinylbenzyl amine:


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Synthesis of 4-vinylbenzyl amine

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a

a

a

a

a

a


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Ligate polymerizable amine

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?


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NMR

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Polymerization of protected molecule

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NMR

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Issues with deprotection

IR could not detect difference fromprotected vs. unprotected

Need higher amount of cysteine within thebackbone

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Alternative synthesis

First attach propargyl amine

Then click azide to alkyne

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NMR

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Evidence of reversibility

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Conclusion

Latent cysteine residues derived frompost-polymerization modification arepossible, yet are not fully optimized.

A facile, high yielding set of reactions havebeen found to produce a protectedcysteine

The deprotection of the cysteine has beenshown

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Future Work

Attach alkyne protected cysteine topolymers with pendant azides

Thiolene/yne chemistry with latent thiolresidue in RAFT

Creation of new materials with pendentcysteines.

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Acknowledgements

Advisor: Dr. Philip Costanzo

Thesis Committee:

Prof. Chad Immoos

Prof. Derek Gragson

Funding provided by an award from theResearch Corporation for Science

Advancement

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Costanzo Research Group

Dahlia Amato

Anton Chavez

Julia Dean

Guilhem Dehoe

Thaddeus Formal

Alex London

Tristan Kleine

Craig Machado

Miles Markmann

Leanna Monteleone

Chris Pattillo

Dimitri Pappademos

Alicia Ross

Kim Varney

Anthony Varni

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Polymers & Coatings Program

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Chemistry & Biochemistry Department

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Thank You

douglas amato, thesis.pptx

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