SYNTHESIS OF MULTI-EPITOPIC GLYCOPEPTIDE-BASED CANCER VACCINES - Biologically-Responsive Hybrid Biomaterials - page 145

A)

CH 2
CH 3

O

O 3 , DM S SPPS

CH 3

A-A-Q-X-X-P-X-X-Y-X-X-E

FmocHN CO 2 H FmocHN CO 2 H

14

12 13

O

X =

CH 3

OH

HO

N
H

O

O

8

HO

A-A-Q-Z-Z-P-Z-Z-Y-Z-Z-E AcHN

O

AcONa pH 5.5
37°C

N

15

Z =

CH 3

N
H

O

B)

OH

HO

O

OH

HO

HO

AcHN

AcONa pH 4 .5

O

O

16

HO

AcHN

+

V-H-A-A-H-A-E-I-N-E-A-G-R-G N

O

V-H-A-A-H-A-E-I-N-E-A-G-R-G

18

H 2 NO O

17

O

Fig. 8. Oxime ligation with: (A) aminooxy carbohydrate; (B) C-glycosyl ketone.

For the construction of the mucin mimic, the authors selected peptide
fragments of endothelial mucin GlyCAM-1 with 12- and 17- residues containing
several unnatural keto amino acids 13 - prepared by reductive ozonolysis of the
commercially available Fmoc-dehydroleucine 12 - in place of serine or threonine
(Figure 8). The final oxime assembly between the aminooxy carbohydrate and
the peptide displaying clustered ketone 14 occurred in sodium acetate buffer
pH 5.5 at 37°C until completeness of the reaction (24h). After RP-HPLC
purification, homogenous oxime-linked multivalent glycopeptide 15 was
recovered in 70% yield. A comparable ligation strategy using C-glycoside
analogues of the Tn antigen was described. This carbohydrate moiety bearing α-
C-glycosyl ketone 16 rather than aminooxy function was introduced either in
single [42] or double [43] copies into an aminooxy containing peptide fragment
of ovalbumin as T-cell epitope 17 (Figure 8). As above, the final oxime ligation
proved efficient but revealed cis-trans isomerism of the oxime linkage in the
glycopeptide 18 .

3.2.2. Native chemical ligation

A previous report with liposome-based constructs showed that the use of dimeric
TACA coupled to a Pam 3 Cys moiety derived from the N -terminal sequence of a
lipoprotein of E. coli resulted in a promising immune response against TACAs