Scheme 3.

Synthesis of cycloSal-based 2-PMPA prodrugs 18a-c and 21.a
aReagents and conditions: (a) SOCl2, CHCl3, 60 °C; (b) Salicyl alcohol or 2-aminobenzyl alcohol derivatives, DIEA (or Et3N), DCM, 0 °C or rt; (c) SOCl2, CHCl3, 60 °C; (d) (2-Amino-3-methylphenyl)methanol, DIEA/pyr, DCM, −78 °C to 0 °C.