Propargylation of arabinogalactan with propargyl halides—a facile route to new functionalized biopolymers

• An efficient method to propargylation of arabinogalactan was developed.
• Etherification of polysaccharide was carried out in aqueous alkaline/toluene system.
• Degree of substitution of arabinogalactan propargyl ethers attains 2.8.
• The structure of ethers was confirmed by IR and 13C NMR.
• Allenyl ethers and silver acetylides of arabinogalactan were prepared.

New arabinogalactan propargyl ethers with degree of substitution (DS) up to 2.8 have been obtained by propargylation of arabino-3,6-galactan (AG) with propargyl bromide (PB) in the two-phase system 30–60% КОН aqueous solution/toluene in the presence of triethylbenzylammonium chloride (TEBAС) or without catalyst (ambient temperature, 1–24 h) in 20–87% yields. The highest yields have been reached using TEBAС as phase-transfer catalyst, though the non-catalytic version proves to be also efficient (DS 2.8, 70% yield). The propargylation of AG is less effective in the systems MОН (M = Na, K)/DMSO. DS of propargyl AG reaches 1.8 (70% yield) when propargyl chloride is used as propargylating agent, while with PB under the same conditions DS value does not exceed 0.4–0.6, the yields being 44–65%. Under the action of t-BuOK/DMSO system, the AG propargyl ethers have been isomerized to the corresponding unstable allenyl ethers. AG propargyl ethers with DS 2.0 have been almost exhaustively metallated with Ag2O/NH3 system to give AG–Ag acetylides derivatives with Ag/CC ratio equaling 0.95.

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