Synthesis and Biological Activity of Arylspiroborate Salts Derived from Caffeic Acid Phenethyl Ester

Scheme 1

Synthesis of CAPE (3) and arylspiroborate salts 4 and 5. Reagents and Conditions. (a) (i) SOCl₂, reflux, 1 h; (ii) HOCH₂CH₂Ph, toluene, pyridine, rt, 12 h. Yield: 78%. (b) Guanidine hydrochloride, CH₃OH–CH₂Cl₂ (1 : 1), rt, 4 h. Yield: 79%. (c) MBH₄, CH₃OH, 6 h (1 h for 5). Yields: 85% for 4, 76% for 5.