Synthesis and NMR characterization of regiocontrolled starch alkyl ethers

Abstract

Selective polysaccharide functionalization is of importance in molecular and supramolecular structure design and the development of new products and properties. As a typical partially branched polysaccharide, starch (72% amylopectin) was selectively and completely alkylated in the secondary positions. Starting from 6-O-thexyldimethylsilyl starch (6-O-TDS starch) prepared regiocontrolled, an effective alkylation takes place by using methyl iodide and benzyl bromide, respectively, and sodium hydride as a base in THF solution. Under these conditions, the silyl ether linkages are stable. The subsequent desilylation proceeded with tetra-n-butylammonium uoride (TBAF) under mild conditions to form the alkyl starches without cleavage of the alkyl ether linkage. The pattern of functionalization could be analyzed by using the silyl alkyl ethers or subsequently 6-O-acetylated derivatives and multidimensional NMR techniques. In the case of the methyl ethers, the substituent distribution could be detected not only in the anhydroglucose units (AGUs), but also in the nonreducing end-groups (NEGs). As a result, the starch ethers are alkylated regiocontrolled in 2,3-di-O (AGU) and 2,3,4-tri-O (NEG) positions.

Studies About the Solvent‐Dependent Substitution Pattern of Starch Acetates

“…On the contrary, the synthesis of regioselectively acetylated starches requires homogeneous reaction conditions. A known approach is the use of protective groups, for example tert ‐hexyldimethylsilyl groups, which can be selectively introduced at position 6 of the AGU, resulting in the acetylation at positions 2 and 3 . Moreover, 2‐ O ‐selectivity was found by the transesterification with vinyl acetate in dimethyl sulfoxide (DMSO) catalyzed enzymatically or in the presence of a sodium salt although this method includes the possibility of cross‐linking caused by the by‐product acetaldehyde .…”

“…A known approach is the use of protective groups, for example tert-hexyldimethylsilyl groups, which can be selectively introduced at position 6 of the AGU, resulting in the acetylation at positions 2 and 3. [11] Moreover, 2-Oselectivity was found by the transesterification with vinyl acetate in dimethyl sulfoxide (DMSO) catalyzed enzymatically or in the presence of a sodium salt although this method includes the possibility of cross-linking caused by the by-product acetaldehyde. [9,12] Up to now, the most promising procedure to yield 2-O-acetyl starch was the homogeneous reaction of starch with acetic acid imidazolides in DMSO, which was a mild and efficient conversion and generated starch acetates free of byproducts.…”

Regiocontroll synthesis cellulose-graft-polycaprolactone copolymer (2,3-di-O-PCL-cellulose) by a new route

“…eXPRESS Polymer Letters Vol.11, No.12 (2017) [991][992][993][994][995][996][997][998][999][1000][1001][1002] Available online at www.expresspolymlett.com https://doi.org /10.3144/expresspolymlett.2017.94 Many attempts have been made to create new cellulose derivative materials with combinations of various functional groups. Selective polysaccharide functionalization is of importance in molecular and supramolecular structure design and the development of new products and properties [7]. In the case of cellulose, the examples of regioselective functionalization described 2,3-di-O-methyl- [8,9], 2,6-di-Othexyldimethylsilyl- [10], 2,6-di-O-acetyl-3-O-methyl cellulose [11] and so on.…”

“…In the case of cellulose, the examples of regioselective functionalization described 2,3-di-O-methyl- [8,9], 2,6-di-Othexyldimethylsilyl- [10], 2,6-di-O-acetyl-3-O-methyl cellulose [11] and so on. In previous literatures, the protection/deprotection procedure is known as an example of the protective group technique in polysaccharide chemistry and as a possibility of controlling subsequent reactions such as etherization and esterification [7][8][9][10][11][12]. Protective groups were used in the selective protection of the secondary side of the cellulose.…”

“…The procedures of protecting hydroxyl groups regioselectively by introducing protective groups and the deprotection can be skipped. A careful check has shown that this method has not been tried by other researchers before [7][8][9][10][11][12][13]. The aim of the present paper is to research the feasibility of this method.…”