Scheme 5. Synthesis of tetravalent and hexadecavalent Tn-oxime vaccine candidates 20 and 21. Reagents and conditions: [a1] Boc-Cys(NPys)NHS (1.5–1.6 eq.), DIPEA (1.5 eq.), DMF, r.t., 30 min, 74% yield; [a2] Boc-Cys(NPys)NHS (1.5 eq.), DMF/PBS (pH 7.4, 10 mM) (1 : 1), 60 min, 41% yield; [b] TFA/CH2Cl2 (1 : 1), r.t., 30 min; [c] 10 (1.1–1.2 eq.), DMF/NaOAc buffer (pH 4.5, 40 mM) (1 : 1), r.t., 20 min.
