Synthesis, Characterization, and Gas Permeation Properties

Amino Acid Esters of Hydroxypropyl Cellulose
use of N-α-,N-ε-di-t-butoxycarbonyl-L-lysine (9.76 g, 28.17 mmol) instead of
N-α-t-butoxycarbonyl-L-glycine. Yield 92%, white solid, 1 H NMR (400 MHz,
d6-DMSO, 80 ºC, ppm): 1.07–1.13 (m, 13.83H, OCHCH3), 1.38 (s, 27.0H,
OCOC(CH3)3), 1.49 (brs, 6.0H, NHCH(CH2CH2)CO), 1.63 (brs, 6.0H,
NHCH(CH2CH2CH2)CO), 2.11–2.15 (m, 6.0H, NHCH(CH2)CO), 3.1 (brs, 6.0H,
NHCH(CH2CH2CH2CH2NH)CO), 3.21–4.65 (m, 18.83H, OCHCH3, OCH, OCH2, and
3.0H, NHCHCO), 4.90 (brs, 2H, OCHCH3); IR (ATR, cm -1 ): 3375, 2978, 2930, 2866,
1750, 1706, 1689, 1599, 1517, 1456, 1399, 1365, 1249, 1163, 1043, 1024, 859, 778,
763; [α]D = –25.6° (c = 0.10 g/dL in CH3OH); anal. calcd for (C67.83H121.66N6.00O24.61)n
(1415.0972)n: C, 57.57; H, 8.67; N, 5.94; O, 27.82, found: C, 57.15; H, 8.34; N, 6.17;
O, 28.34.
Determination of the Degree of Substitution. The average number of
hydroxypropyl substituents per anhydroglucose unit (molar substitution; MS) in
hydroxypropyl cellulose (1) was determined by 1 H NMR by calculating the integration
ratio of proton on the anomeric carbon of anhydroglucose unit (AGU) to those of the
terminal methyl protons of hydroxypropyl group. On the other hand, the
incorporation of amino acid moieties into hydroxypropyl cellulose has been
accomplished through esterification and the extent of substitution of hydroxy protons
of 1 by aminoalkanoyl pendants has been denoted by DSEst throughout this
contribution, which was determined by calculating the integration ratio of the peaks
arising due to the methyl protons of hydroxypropyl pendants and those of t-Boc
termini of the amino acid moieties.
Results and Discussion
Amino Acid Ester Synthesis. The amino acid esterification of
hydroxypropyl cellulose was accomplished by coupling the hydroxy functionalities of
hydroxypropyl cellulose (1) with the carboxy termini of amino acids;
N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride (EDC·HCl) was
employed as a condensating agent and 4-(dimethylamino)pyridine (DMAP) as a base,
142