Acylation of Pullulan by Ring-Opening of Lactones

Abstract

In this paper, we report on the production of modified pullulan derivatives that have been produced in solution by ring-opening ε-caprolactone and [l]-lactide using a tin octanoate [Sn(Oct)2] catalyst system in DMSO. These derivatives designated as hexanoates (1 and 2) and dilactates (4−7) have been characterized and have varying degrees of substitution (DS). 1 and 2 were characterized by interesting thermal properties as well as crystalline morphology. From DSC analysis, 2, unlike the parent polysaccharide, appears to melt at 114 °C. The crystalline morphology of this polymer was characterized by X-ray powder diffraction and d spacings were calculated. This pullulan derivative possessed new crystallographic reflections not seen in either pullulan or poly (ε-caprolactone). The pullulan-6 dilactate samples (4−7), produced had DS values ranging from 0.1 to 0.75. Depending upon the DS, these samples were soluble in a wide range of organic solvents including acetone and methanol. Although these materials did not exhibit any observable melting transitions from inspection of DSC, glass transition temperatures were detected for 5 [DS = 0.21], 6 [DS = 0.44], and 7 [DS = 0.80], at 130, 120, and 90 °C, respectively. As confirmed by 13C NMR, the ring-opening process for all of these pullulan derivatives appears to be taking place through an acyl−oxygen cleavage, producing an ester linkage to the backbone with a hydroxy terminus.

Self‐organized nanogels from pullulan‐g‐poly(L‐lactide) synthesized by one‐pot method: Physicochemical characterization and in vitro doxorubicin release

“…Via the dialysis process, the pullulan, which has a low molecular weight, was removed from the pullulan solution, thus resulting in a narrower molecular weight distribution and yielding a pullulan of slightly greater molecular weight. 13 The resultant solution was lyophilized for 3 days and stored in a dry desiccator. L-Lactide, TEA, and DMSO were acquired from Aldrich.…”

“…The ratio of integration of peaks at 1.4 ppm (the lactide methyl protons, 6H) and 5.2 ppm (3H) was used to determine the degree of substitution (DS) for the polymers. 13 The FTIR spectra were recorded on a Perkin-Elmer FTIR system (Spectrum GX; Perkin-Elmer, Waltham, MA) at an ambient temperature with the use of KBr pellets. By observing the new peaks and comparing them with those of the raw pullulan on the spectroscopy, the formed chemical bonds were verified.…”

“…12 It is a linear polysaccharide harboring maltotriosyl repeating units united by a-(1!6)-linkages or chains of D-glucopyranosyl units that regularly alternate between one a-(1!6)-D and two a-(1!4)-D linkages. 13,14 Pullulan has some limitations in processing as a consequence of its melting temperature and, thus, we conducted acylation with acetic anhydride and L-lactide in an effort to improve its properties.…”

“…However, it required more than 1 week to synthesize when their method was used. 13 In the same journal, another group reported the graft polymerization of Llactide on pullulan via the trimethylsilyl (TMS) protection method and studied their degradation properties. 15 However, three steps were required for the polymerization of this PUPL, and it was difficult to introduce the small number of poly(L-lactide) (PLLA) graft chains via this synthetic method.…”

Nanoparticles prepared by blending of carboxylic acid terminated poly(ε‐caprolactone) and L‐phenylalanine substituted dextran

“…Thus, they are commonly prepared from biodegradable polymer such as polysaccharides and biocompatible polyesters by self-assembling of polysaccharidepolyester copolymers. [6][7][8] Methods for preparing polysaccharide-polyester copolymer include a catalytic ring-opening polymerization of monomers (lactide or caprolactone) in the presence of polysaccharides [9][10][11] and bulk polymerization of monomers in the presence of partially protected hydroxyl groups of polysaccharides, [12][13][14] followed by deprotection. The first approach is the difficulty to obtain controlled structures because all the hydroxyl groups on the polysaccharides, except the ones sterically hindered, initiate the polymerization.…”