Collagen mimetic dendrimers

Article abstract of DOI:10.1021/ja021203l

The synthesis of single-chain, scaffold (TRIS)- and dendrimer-assembled collagen mimetics (both Gly-Pro-Nleu and Gly-Nleu-Pro sequences) is reported. From the CD spectra and the thermal denaturation studies it can be readily seen that mimetics prepared fr

Full text of DOI:10.1021/ja021203l

Published on Web 11/28/2002
Collagen Mimetic Dendrimers
Garth A. Kinberger, Weibo Cai, and Murray Goodman*
Department of Chemistry and Biochemistry, UniVersity of California - San Diego, La Jolla, California 92093
Received September 23, 2002
Collagen is the main structural protein in mammals and consists
of triple helical peptides composed of Gly-Xaa-Yaa trimer repeats.1-5
Templates,6 disulfides,7 and transition metals8 have been utilized
to create protein-like structures.9-11 We report here the synthesis
Figure 1. The Z-protected TRIS scaffold (Z-TRIS[OH]3).
and conformational properties of 162-residue collagen mimetic
dendrimers which exhibit enhanced triple helical stability compared
to equivalent scaffold terminated structures.
Many synthetic collagen mimetics exhibit triple helical conforma-
tions.12-15 In this communication we also report the utilization of
a new scaffold to assemble collagen mimetics: N-(benzyloxycar-
bonyl)-tris(carboxyethoxymethyl)aminomethane (Z-TRIS[OH]3),
possessing three carboxyl groups for peptide chain attachment and
a protected primary amine for further reaction (Figure 1).16
The collagen-like dendrimers were built from Gly-Pro-Nleu and
Gly-Nleu-Pro sequences (where Nleu denotes N-isobutylglycine).
The Z-protecting groups on the scaffold-terminated peptides were
removed and allowed to react with trimesoyl chloride to create the
dendritic structures (Figure 2 and Supporting Information). Figure
2 shows the structure of the dendrimer built from the Gly-Pro-
Nleu sequence, TMA[TRIS[(Gly-Pro-Nleu)6-OMe]3]3 where TMA
denotes the trimesic acid core. We also prepared an analogous den-
drimer from the Gly-Nleu-Pro sequence which possess a â-alanine
spacer between the TRIS amine and the TMA core, TMA[â-Ala-
TRIS[(Gly-Nleu-Pro)6-OMe]3]3 (see Supporting Information Figure
S1).
Figure 2. The collagen mimetic dendrimer TMA[TRIS[(Gly-Pro-Nleu)6-
OMe]3]3.
The triple helicity of all structures were determined by thermal
denaturation monitored by optical rotation and circular dichroism
measurements (Figures 3-5). These spectroscopic studies were
carried out in H2O as well as the triple helicity-enhancing solvent
ethylene glycol:H2O (EG:H2O, 2:1, v/v).14
The optical rotation data shown in Figures 3 and 4 indicate that
the molecules studied exhibit a cooperative melting transition with
the exception of the single-chain compounds shown in Figure 3A
and B which do not exhibit a transition in H2O. A shallow transition
for the linear molecules can be seen in EG:H2O (2:1) (Figure 4A
and B). This indicates that the single-chain structures studied form
triple helices to a small extent in EG:H2O (2:1).
Figure 3. Thermal denaturations measured by changes in optical rotations
carried out in H2O (0.2 mg/mL): (A) Boc-(Gly-Nleu-Pro)6-OMe (0), Boc-
â-Ala-TRIS[(Gly-Nleu-Pro)6-OMe]3 (2) and TMA[â-Ala-TRIS[(Gly-Nleu-
Pro)6-OMe]3]3 (9); (B) Boc-(Gly-Pro-Nleu)6-OMe (0), Boc-â-Ala-TRIS-
[(Gly-Pro-Nleu)6-OMe]3 (2) and TMA[TRIS[(Gly-Pro-Nleu)6-OMe]3]3* (9,
*0.1 mg/mL).
The CD data shown in Figure 5A are indicative of a triple helical
conformation for the scaffold-assembled and dendritic Gly-Pro-
Nleu-containing molecules at low temperature, whereas the single-
chain molecule is not triple helical. In Figure 5B the data were
acquired at 22 °C. Only the dendrimer remains triple helical, while
the scaffold-terminated structure and the single-chain molecule are
not triple helical. This result is consistent with data from the melting
curves contained in Figure 3B. The Gly-Nleu-Pro-containing struc-
tures also exhibit CD spectra of triple helical collagen-like molecules
except for the single-chain compound in H2O (see Supporting
Information Figure S2 and S3).
Figure 4. Thermal denaturations measured by changes in optical rotations
carried out in EG:H2O (2:1, 0.2 mg/mL): (A) Boc-(Gly-Nleu-Pro)6-OMe
(0), Boc-â-Ala-TRIS[(Gly-Nleu-Pro)6-OMe]3 (2) and TMA[â-Ala-TRIS-
[(Gly-Nleu-Pro)6-OMe]3]3 (9); (B) Boc-(Gly-Pro-Nleu)6-OMe (0), Boc-
â-Ala-TRIS[(Gly-Pro-Nleu)6-OMe]3 (2) and TMA[TRIS[(Gly-Pro-Nleu)6-
OMe]3]3* (9,*0.1 mg/mL).
It can be readily seen from Figures 3 and 4 that mimetics
prepared from the Gly-Nleu-Pro sequence form more thermally
* To whom correspondence should be addressed. E-mail: mgoodman@
ucsd.edu.
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J. AM. CHEM. SOC. 2002, 124, 15162-15163
10.1021/ja021203l CCC: $22.00 © 2002 American Chemical Society

C O M M U N I C A T I O N S
To determine whether the stabilizing effect of the dendrimer is
inter- or intramolecular, we measured the concentration dependence
for the melting transition and found no effect between 0.05 and
2.0 mg/mL in H2O (see Supporting Information Figure S4). We
therefore believe that the stabilizing effects arise from an intramo-
lecular clustering of the triple helical arrays about the core structure.
Figure 6 shows a schematic representation for such a clustered
structure. This ensemble excludes solvent from the interior portion
of the array which stabilizes the triple helical bundle.
Acknowledgment. This project is funded by the NSF bioma-
terials division, DMR9802329.
Figure 5. CD spectra in H2O of Boc-(Gly-Pro-Nleu)6-OMe (green, 0.2
mg/mL), Boc-â-Ala-TRIS[(Gly-Pro-Nleu)6-OMe]3 (blue, 0.2 mg/mL) and
TMA[TRIS[(Gly-Pro-Nleu)6-OMe]3]3 (red, 0.1 mg/mL) at (A) 8 °C and
(B) 22 °C.
Supporting Information Available: Experimental details and
figures (PDF). This material is available free of charge via the Internet
at http://pubs.acs.org.
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