Development of cancer vaccines from fully synthetic mucin-based glycopeptide antigens. A vision on mucins from the bioorganic chemistry perspective - Carbohydrate Chemistry: Chemical and Biological Approaches - page 541

acetonide groups using I 2 in MeOH gave rise to the versatile triol 21 or 22,
which could readily be converted to the peracetyl Tn precursors. Alter-
natively the triols could be transformed, via resilylation with TBSCl, into
diol 3-acceptor 23 or 24, or by benzylidene formation to give specific
position 3 acceptor 25 or 26. This methodology was used to prepare
substantial quantities of the Tn antigen. In addition, we used these
intermediates for the ecient preparation of several O-linked tumor-
associated antigens such as TF, Sialyl-Tn and Sialyl-T antigens.
For the synthesis of the Tn cluster, we used the peracetyl Tn derivatives
23/24 and 25/26, and following standard, IIDQ-mediated, peptide coup-
ling procedures the trimeric clusters 31 and 32 were prepared (Scheme 7).
In these constructs, the amino terminus was acetylated and the
carboxy terminus liberated for further modification. Such derivatization
included coupling of 33/34 to a synthetic lipopeptide, tripalmitoyl-S-
glycerylcysteinylserine (Pam 3 CysSer, 35) as immunological activator to
afford fully synthetic derivatives 36 and 37. Alternatively, after global
deprotection of 38, conjugation of 39 to an immunogenic carrier protein
such as BSA or KLH produced the corresponding functional vaccines
(Scheme 8). 16
The initial experiments were to evaluate the antibody response to
vaccination of mice with either Tn(c)-pam lipopeptide 36 or more con-
ventional Tn(c)-KLH or Tn(c)-BSA conjugates. 16 In the bioconjugation
event, about 317 clusters per KLH were introduced, while BSA showed only
7 clusters per protein. These conjugates plus the adjuvant QS-21, as well as
36 in intralipid, or 36 in intralipid plus QS-21 were used to vaccinate
groups of five mice, and all of these constructs proved to be immunogenic.
Construct 39 conjugated with KLH plus QS-21 was the optimal vaccine,
inducing high IgM and IgG titers by ELISA, whereas sera of mice im-
munized with 36 [Tn(c)-Pam] in conjunction with QS-21 failed to show
strong reaction. The cell surface reactivities of anti-Tn(c) antibodies were

AcO OAc OH OAc

HO AcO

O O O

a b

AcO

HO AcO

N H 2

N HFmoc N HFmoc

AcHN N 3 AcHN

O

OBn O OBn O OH

23 R=H
24 R=Me

21 R=H
22 R=Me

25 R=H
26 R=Me

O

R O O

R R

c

OAc

AcO OAc AcO

AcO OAc

O

O

O

AcO AcO

AcO

AcHN AcHN

AcHN

O R

O R R O

O d, c, d, e

O

N

N

OR 1

R 1 =Bn
R 1 =H

OBn

FmocHN

AcHN H f

O

O O

R O

R O

NHAc

NHAc

OAc

OAc

27 R=H
28 R=Me

29 R=H, R 1 =Bn
30 R=Me, R 1 =Bn

31 R=H, R 1 =H
32 R=Me, R 1 =H

O

O

OAc

AcO

OAc

AcO

Scheme 7 Synthesis of the trimeric Tn cluster. (a) 1. Ac 2 O, DMAP, Et 3 N, CH 2 Cl 2 , 90%; 2.
AcSH; 3. 20% morpholine in DMF, 5 min; (b) Ac 2 O, DMAP, Et 3 N, CH 2 Cl 2 , 90%; 2. AcSH;
3. Pd/C, H 2 , MeOH, H 2 O, 75%. (c) 25/26 IIDQ, CH 2 Cl 2 , 85-97%; (d) 20% morpholine in
DMF, 90-100%, (e) Ac 2 O, CH 2 Cl 2 , 70-76%; (f) Pd/C, H 2 , MeOH, H 2 O, 85-95%.