Photolabile Protection and Deprotection Strategy in Designing Functionalized Surface for Tissue Grow

1
Photolabile Protection and Deprotection Strategy
in Designing Functionalized Surface for Tissue
Growth

• Mei Wang, G. L. Baker, and M. R. Smith III
• Department of Chemistry, and Center for
  Fundamental Materials Research
• Michigan State University, East Lansing, Michigan
  48824

2
Introduction

• Poly(lactide) and its copolymers have been
  used as biomedical materials due to their
  biocompatibility. In recent years, many studies
  have shown their application in tissue
  engineering as a biocompatible and dissolvable
  scaffold1. Our group has worked out chemistry to
  synthesize functionalized copolymers and coupling
  reactions on the polymer surface. As for tissue
  growth on surfaces, cell geometry has been shown
  to be a critical factor for death and growth of
  cell2. We are exploring the modification of the
  surface of in a well controlled fashion.
  Therefore, a strategy for patterning the surface
  of polymer with specific geometry would be
  desirable. Photolabile protection and
  deprotection strategies could be a good solution
  to this problem. Photolabile protecting groups
  are used in solid support peptide synthesis
  because they can be removed without harsh acidic
  or basic conditions, and usually give minimal
  byproducts3. Irradiation of the polymer surface
  through a photolithographic mask, functional
  groups can be exposed with designed pattern.

3
Biodegradable Polymer Synthesis

• Poly(L-lactic acid-co-diallylglycolide)
  (PLLA-co-DAG) was prepared by bulk polymerization
  of L-lactide and diallylglycolide. Controlled
  polymerization gives 10 to 15 mole percent of
  allyl unit. Further oxidation at the terminal
  double bond gives functionality for peptide or
  cell attachment4.

4
Photolabile Protection-deprotection for Cell
Growth

• Silicon wafer is spin-coated with polymer that
  has functionalized side chain being protected by
  photolabile protecting groups. Then, exposed the
  surface to UV light through a mask containing the
  desired pattern.
• After irradiation, protecting group is removed at
  the exposed region, and therefore the surface is
  patterned with functional groups.
• Cells can then grow on polymer surface with
  certain geometry to optimize cell surface
  interaction.

5
Protecting Group Choice

• 3,5 dimethoxybenzyloxycarbonyl protecting
  group was our previous choice for this approach.
  It worked very nicely for model compound
  allyamine. But problems occured while applying it
  on polymer. UV absorption of the chromophore
  overlaps with absorption of polymer backbone.
  Degradation occured while irradiating at wave
  length shorter than 290. But while irradiate at
  longer wavelength (gt290), quantum yield became
  very low.

Anthraquinon-2-ylmethoxycarbonyl (Aqmoc) is a
good photolabile protecting group for cell
biological applications5. It has high efficiency
of photolysis at around 350, which will minimize
cell damage during irradiation, for our system,
also avoid degradation of polymer backbone.
Protecting Group Polymer Backbone
UV-Visc spectrum of 3,5 dimethoxybenzyloxycarbonyl
and Polymer Back Bone
6
Side Chain Functionalization

• PLLA-co-DAG was functionalized using
  hydroboration/oxidation to convert the terminal
  double bond of the side chain to a terminal
  hydroxyl group for further chemistry reactions on
  polymer surface.

7
Anthraquinon-2-ylmethoxycarbonyl (Aqmoc)
Protecting Group Synthesis
8
Photo-deprotection
Protected Polymer Polymer After
Photolysis PLLA-g-PH
VU-Visc Spectrum for Polymer Before and After
Photolysis
9
Molecular Weight Data
During Hydroboration/Oxidation, the molecular
weight of polymer remains the same. However some
molecular weight decrease was observed after
coupling reactions at the presence of DMAP. There
could be a base catalyzed depolymerization during
the reaction6. After Photolysis, molecular weight
of polymer slightly increased, and solubility of
the resulting polymer became poorer. That could
indicated some polymer cross linking under
photochemical conditions.
10
Conclusion

• Photolabile protecting groups can be
  attached on functionalized polymer side chain
  with good conversion. The reactivity and polymer
  stability under photochemical conditions has also
  been tested. Wavelength is found to be a very
  important consideration for these deprotection
  reactions. A protecting group needs to have
  absorption at a high enough wavelength (gt280) to
  avoid polymer degradation. Aqmoc group meets this
  criterion as demonstrated by our model reaction.
  Protection and deprotection on polymer also
  worked fairly well.
• Future work will focus on studying the
  overall effect of molecular weight during
  coupling reactions and photolysis and optimizing
  reaction conditions to keep molecular eight
  constant. Protection and deprotection efficiency
  will also be further quantified. Photolysis of
  spin coated silicon wafer through
  photolithographic mask will be carried out next.

Future Work
11
Reference

• Ma et al,. J. Biomed. Mater Res. 2001, 54,
  284-293.0
• Christopher C. Chen, Milan Mrksich, Sui Huang,
  Ceorge M. Whitesides, Donald Ingber, Science 276
  (5317) 1425-1428 May 1997
• Christan G. Bochet, J. Chem. Soc.,Perkin Trans 1,
  2002, 125-142
• C. P. Radano, G. L. Baker, M. R. Smith, III,
  Polymer Preprints (American Chemical Society,
  Division of Polymer Chemistry) (2002), 43(2),
  727-728.
• T. Furuta, Y. Hirayama, M. Iwamura , Organic
  Letters, 3 (12) 1809-1812 JUN 14 2001
• Frederik Nederberg, Eric F. Connor, Thierry
  Clausser and James L. Hedrick, Chem. Commun.,
  2001,2066-2067

Acknowledgement

• Dr. M. R. Smith III
• Dr. G. L. Baker
• Smith and Baker group members.
• Center for Fundamental Materials Research