Pd-catalyzed cross-coupling of arabinogalactan propargyl ethers with 5-bromosalicylic acid

New salicylate derivatives of arabinogalactan have been synthesized in up to 90% yield by cross-coupling of propargyl ethers of arabinogalactan with 5-bromosalicylic acid salts. The reaction proceeds in the presence of the catalytic system Pd(PPh₃)₄/PPh₃ with CuBr (CuI), and piperidine or 1,8-diazabicyclo-[5.4.0]-undec-7-ene (DBU) as a base in DMSO at 70-95 °С. The propargyl groups of the starting arabinogalactan ethers are converted into propinylsalicylate ones with 35 and 50% conversion depending on the nature of the base used. Degree of arabinogalactan substitution with propynyl salicylate fragments reaches 1.0 and 0.7 in the reactions with piperidine and DBU, respectively. In the case of piperidine, along with the main process, intensive unprecedented (for Sonogashira reaction) hydroamination of propargyl groups is also observed, followed by hydrolysis of unstable enamines. The products have been characterized by IR, ¹Н and ¹³С NMR, UV spectroscopy as well as elemental analysis and gel permeation chromatography. Salicylate derivatives of arabinogalactan show high activity in prolonging the activated partial thromboplastin time (APTT), whereas neither the arabinogalactan nor propargyl ethers of arabinogalactan nor salicylic acid salts have obvious effects.