Availability and state of order of hydroxyl groups on the surfaces of microstructural units of crystalline cotton cellulose

The relative accessibilities of the hydroxyl groups of the D-glucopyranosyl units of hydrocellulose have been studied by means of the reaction of N,N-diethylaziridinium chloride, which produces 2-(diethylamino)ethyl cellulose. The deviation in the distribution of substituents among the 2-O-, 3-O-, and 6-O-positions of the D-glucopyranosyl residues in a hydrocellulose from that in a disordered cellulose in which the three types of hydroxyl groups are equally accessible is the basis for estimating the selective accessibilities of the hydroxyl groups in the crystalline cellulose. A particular hydrocellulose, lying within the range of leveling-off degree of polymerization, was studied in detail; this hydrocellulose, designated EHC (“Exemplar Hydrocellulose”), was formed from fibrous cotton by hydrolysis for 0.67 hr in 2.5N hydrochloric acid at reflux. EHC exhibited higher selective accessibility (larger deviation from equal accessibility) of the hydroxyl groups at C-2, C-3, and C-6, than samples of hydrocellulose formed in shorter or longer periods of hydrolysis. This selective accessibility is discussed in terms of intra- and intermolecular hydrogen bonding on the surfaces of crystalline microstructural units in EHC.     

Hydrogen bonds in regioselectively substituted cellulose derivatives

Formation of hydrogen bonds in various cellulose derivatives, 2,3-di-O- and 6-O-substituted cellulose ethers, were characterized by FTIR and solid-state CP/MAS¹³C-NMR. The polymers were synthesized by regioselective substitution of hydroxyl groups and had a uniform structure. Since their three hydroxyl groups (OH) are selectively blocked, the cellulose derivatives appeared to form specific inter- and intramolecular hydrogen bonds. The characteristic OH stretching frequencies in IR spectra and the C-1 chemical shift in CP/MAS spectra of 6-O-substituted cellulose derivatives indicated existence of two equivalent intramolecular hydrogen bonds between ether oxygen and OH groups at 3-OH-O5′ and O6-HO-2′ [Figure 3(C)]. Influence of the substituents at the C-6 position on the formation was not significant except trityl group. Behavior of the hydrogen bonds in 6-O-tritylcellulose were also discussed. © 1994 John Wiley & Sons, Inc.     

27-Ald-triterpenoid saponins from Adina rubella

Four new triterpenoid saponins were isolated from the roots of Adina rubella Hance. They were characterized as adinaic acid 3β-O-[α-L-rhamnopyranosyl(l→2)-β-D-glucopyranosyl(l→2)-β-D-glucurono-pyranoside-6-O-methyl ester]-28-O-β-D)-glucopyranoside, adinaic acid 3β-O-[α-L-rham-nopyranosyl(l→2)-β-D-glucopyranosyl(l→2)-β-D-glucuronopyranoside-6-O-butyl ester]-28-O-β-D-glu-copyranoside, adinaic acid 3β-O-[β-D-glucopyranosyl(l→2)-β-D-glucopyranosyl]-(28→1)-β-D-gluco-pyranosyl(l→6)-β-D-glucopyranosyl ester, 27-hydroxyursolic acid 3β-O-[α-L-rhamnopyranosyl (l→2)-β-O-glucopyranosyl(l→2)-β-D)-glucuronopyranoside-6-O-methyl ester]-28-O-β-D)-glucopyranoside. Their structures were elucidated by spectral methods, especially with the aid of 2D NMR techniques. Their complete assignments of the 1H and 13C NMR signals were carried out.     

Hydrogen bonding on accessible surfaces of cellulose from various sources and relationship to order within crystalline regions

Celluloses from a variety of common sources were analyzed for availabilities of O(2)H, O(3)H, and O(6)H in order to estimate the extent of hydrogen bonding on accessible fibrillar surfaces. Celluloses from flax, ramie, sisal, and wood (both cellulose I and II from wood) together with liquid NH₃-swollen cotton and NaOH-swollen cotton (cellulose II) had relative availabilities similar to those of native cotton. Celluloses from Valonia centricosa and in rayon samples stood apart from each other and from the “cotton family.” The difference between Valonia and cotton celluloses appears to result, in addition to the accepted smaller, less perfect crystallites in cotton, from an O(2)H hydrogen bond which is likely the intramolecular bond between O(2)H and O(6′)H that is present in Valonia and absent in cotton. Rayon samples also showed evidence of similar bonds involving O(2)H on accessible surfaces. Since the regenerated rayons had relative availabilities different from those of mercerized cotton and wood cellulose samples, it is proposed that chain packing arrangements are not the same in these two types of cellulose II.     

Three 1,6-anhydro-β-d-glycopyranose derivatives

Two of the title compounds, 1,6-an­hydro-2,3-O-(S)-benzyl­idene-β-d -manno­pyran­ose, C₁₃H₁₄O₅, (I), and 1,6-an­hydro-4-O-benzyl-β-d -manno­pyran­ose, C₁₃H₁₆O₅, (II), are derived from β-d -manno­pyran­ose, while the third, 1,6-an­hydro-3,4-O-(S)-benzyl­idene-β-d -galacto­pyran­ose, C₁₃H₁₄O₅, (III), is derived from β-d -galacto­pyran­ose. In the crystal packing, each hydroxyl group is involved in O—H⃛O hydrogen bonds, where the acceptor group is the other hydroxyl group in (II), or the endocyclic O atoms of the dioxolane [in (I)], an­hydro [in (II)] or pyran­ose [in (III)] rings. Differences in the crystal packing arise from the contrasting O—H⃛O hydrogen-bonding environments.     

The nature of accessible surfaces in the microstructure of cotton cellulose

The accessible regions in cotton cellulose were tagged by the introduction of diethyl-aminoethyl (DEAE) substituents at DS = 0.034 without other substantial changes in structure. Evidence from rates of hydrolysis of this DEAE cotton to hydrocelluloses and from the composition and structure of the solubilized and insoluble fractions provides the basis for considerable detail regarding two types of accessible regions in the cotton fiber; these are identified as accessible surfaces of elementary fibrils. One type of accessible surface is characterized by molecular chain segments which are distorted and disordered by tilt/twist strain that is concentrated in this segment of the elementary fibril; the second type of accessible surface is characterized by a relatively high degree of order which reflects the high level of crystallinity within the interior of this unstrained segment of the elementary fibril. Substantial differences between these accessible surfaces are discussed. It is estimated that chain segments on accessible surfaces of the first type are substantially disordered, i.e., approximately 60–90% of the D -glucopyranosyl units are dislocated from positions of perfect crystalline order. Accessible surfaces of the second type are quite highly ordered, i.e., only 5–30% of the D -glucopyranosyl units dislocated.     

Enzymatic synthesis of novel quercetin sialyllactoside derivatives

Quercetin and its derivatives are important flavonols that show diverse biological activity, such as antioxidant, anticarcinogenic, anti-inflammatory, and antiviral activities. Adding different substituents to quercetin may change the biochemical activity and bioavailability of molecules, when compared to the aglycone. Here, we have synthesised two novel derivatives of quercetin, quercetin-3-O-β-d-glucopyranosyl, 4′′-O-d-galactopyranosyl 3′′′-O-α-N-acetyl neuraminic acid i.e. 3′-sialyllactosyl quercetin (3′SL-Q) and quercetin-3-O-β-d-glucopyranosyl, 4′′-O-β-d-galactopyranosyl 6′′′-O-α-N-acetyl neuraminic acid i.e. 6′-sialyllactosyl quercetin (6′SL-Q) with the use of glycosyltransferases and sialyltransferases enzymes. These derivatives of quercetin were characterised by high-resolution quadrupole-time-of-flight electrospray ionisation mass spectrometry (HR-QTOF-ESI/MS) and ¹H and ¹³C nuclear magnetic resonance (NMR) analyses.     

Preparative isolation and purification of anthocyanins from purple sweet potato by high-speed counter-current chromatography

High-speed counter-current chromatography (HSCCC) was applied to the preparative isolation and purification of peonidin 3-O-(6-O-(E)-caffeoyl-2-O-β-D -glucopyranosyl-β-D -glucopyranoside)-5-O-β-D -glucoside ( 1 ), cyanidin 3-O-(6-O-p-coumaroyl)-β-D -glucopyranoside ( 2 ), peonidin 3-O-(2-O-(6-O-(E)-caffeoyl-β-D -glucopyranosyl)-6-O-(E)-caffeoyl-β-D -glucopyranoside)-5-O-β-D -glucopyranoside ( 3 ), peonidin 3-O-(2-O-(6-O-(E)-feruloyl-β-D -glucopyranosyl)-6-O-(E)-caffeoyl-β-D -glucopyranoside)-5-O-β-D -glucopyranoside ( 4 ) from purple sweet potato. Separation of crude extracts (200 mg) from the roots of purple sweet potato using methyl tert-butyl ether/n-butanol/acetonitrile/water/trifluoroacetic acid (1:4:1:5:0.01, v/v) as the two-phase solvent system yielded 1 (15 mg), 2 (7 mg), 3 (10 mg), and 4 (12 mg). The purities of 1 – 4 were 95.5%, 95.0%, 97.8%, and 96.3%, respectively, as determined by HPLC. Compound 2 was isolated from purple sweet potato for the first time. The chemical structures of these components were identified by ¹H NMR, ¹³C NMR and ESI-MSⁿ.     

Mimics of the Structural Elements of Type III Group B Streptococcus Capsular Polysaccharide. Part I: Synthesis of a Carboxylate-Containing Pentasaccharide

Abstract

A carboxylate-containing pentasaccharide, methyl O-(β-d-galactopyranosyl)-(1→4)-O-(β-d-glucopyranosyl)-(1→6)-O-{3-O-[(S)-1-carboxyethyl]-β-d-galactopyranosyl-(1→4)-O}-(2-acetamido-2-deoxy-β-d-glucopyranosyl)-(1→3)-β-d-galactopyranoside (27) was synthesized by block condensation of suitably protected donors and acceptors. Phenyl 3-O-benzyl-4,6-di-O-chloroacetyl-2-deoxy-2-phthalimido-1-thio-β-d-glucopyranoside (17) was condensed with methyl 2,4,6-tri-O-benzyl-β-d-galactopyranoside (4) to afford a disaccharide, methyl O-(3-O-benzyl-4,6-di-O-chloroacetyl-2-deoxy-2-phthalimido-β-d-glucopyranosyl)-(1→3)-2,4,6-tri-O-benzyl-β-d-galactopyranoside (18). Removal of chloroacetyl groups gave 4,6-diol, methyl 0-(3-O-benzyl-2-deoxy-2-phthalimido-β-d-glucopyranosyl)-(1→3)-2,4,6-tri-O-benzyl-β-d-galactopyranoside (19), in which the primary hydroxy group (6-OH) was then selectively chloroacetylated to give methyl O-(3-O-benzyl-6-O-chloroacetyl-2-deoxy-2-phthalimido-β-d-glucopyranosyl)-(1→3)-2,4,6-tri-O-benzyl-β-d-galactopyranoside (20). This acceptor was then coupled with 2,4,6-tri-O-acetyl-3-O-[(S)-1-(methoxycarbonyl)ethyl]-α-d-galactopyranosyl trichloroacetimidate (14) to afford a trisaccharide, methyl O-{2,4,6-tri-O-acetyl-3-O-[(S)-l-(methoxycarbonyl)ethyl]-β-d-galactopyranosyl}-(1→4)-O-(3-O-benzyl-6-O-chloroacetyl-2-deoxy-2-phthalimido-β-d-glucopyranosyl)-(1→3)-2,4,6-tri-O-benzyl-β-d-galactopyranoside (21). Removal of the 6-O-chloroacetyl group in 21 gave 22, which was coupled with 4-O-(2,3,4,6-tetra-O-acetyl-β-d-galactopyranosyl)-2,3,6-tri-O-acetyl-α-d-glucopyranosyl trichloroacetimidate (23) to yield protected pentasaccharide 24. Standard procedures were used to remove acetyl groups and the phthalimido group, followed by N-acetylation, and debenzylation to yield pentasaccharide 27 and a hydrazide by-product (28) in a 5:1 ratio, respectively. Compound 27 contains a complete repeating unit of the capsular polysaccharide of type III group B Streptococcus in which terminal sialic acid is replaced by an (S)-1-carboxyethyl group.     

Assessment of the state of order of hydroxyl groups and of molecular segments in hydrocellulose

Through a study of the selective distribution of substituents introduced into hydrocellulose from reaction with N,N-diethylaziridinium chloride, the change in selective availability of hydroxy groups at C-2, C-3, and C-6 has been followed as a function of duration of hydrolysis to form the hydrocellulose. The hydrocellulose formed at a particular duration of hydrolysis showed maximum selective availability of hydroxyl groups; this was found to coincide with minimum moisture regain and minimum breadth at half height for 101 , 101, and 002 peaks in x-ray diffractograms. These points are discussed in terms of the structures of the hydrocelluloses at various stages of hydrolysis and in terms of the sequence of changes which is now associated with the conversion of fibrous cotton to “exemplar hydrocellulose,” i.e., the hydrocellulose having the highest degree of crystalline order, and subsequently, to less highly ordered hydrocelluloses.     

Two new triterpenoids from Nauclea officinalis

Two new triterpenoids and three 27-nor-triterpenoids were isolated from the stems (with bark) of Nauclea officinalis. Their structures were identified to be 2β,3β,19α,23-tetrahydroxy-urs-12-en-28-oic acid (1), 2β,3β,19α,23-tetrahydroxy-urs-12-en-28-O-[β-d-glucopyranosyl (1-2)-β-d-glucopyranosyl] ester (2), pyrocincholic acid 3β-O-α-l-rhamnopyranoside (3), pyrocincholic acid 3β-O-α-l-rhamnopyranosy1-28-O-β-d-glucopyranosyl ester (4), pyrocincholic acid 3β-O-α-l-rhamnopyranosy1-28-O-β-d-glucopyranosyl-(1-6)-β-d-glucopyranosyl ester (5) by spectroscopic methods including 1D, 2D NMR and HR-MS analyses. The cytotoxic activity of 1–5 against lung cancer A-549 cells was also investigated.     

A Comparison in the Efficiency of Six Standard 2-Amino-2-Deoxy-Glucosyl Donors for the Synthesis of (2-Deoxy-2-Phthalimido-β-D-Glucopyranosyl) (1→ 4)-β-D-Glucopyranosides.

ABSTRACT

A systematic study is presented for the most common methods used for the preparation of the disaccharide benzyl O-(3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido-β-D-glucopyranosyl)-(1→'4)-3,6-di-O-benzoyl-2-deoxy-2-phthalimido-β-D-glucopyranoside (9) from “standard 2-amino-2-deoxyglucopyranosyl donors” 1-6 and benzyl 3,6-di-O-benzoyl-2-deoxy-2-phthalimido-β-D-glucopyranoside (7) as an acceptor. It was found that the highest yield was obtained when the trichloroacetimidate derivative 1 was coupled to the 4 position of acceptor 7. In an analogous manner, the disaccharides allyl O-(3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido-β-D-glucopyranosyl)-(1→'4)-3,6,-di-O-benzoyl-2-deoxy-2-phthalimido-β-D-glucopyranoside (10), benzyl O-(3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido-β-D-glucopyranosyl)-(1→'4)-3,6-di-O-benzoyl-2-deoxy-2-phthalimido-β-D-galactopyranoside (12), and allyl O-(3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido-β-D-glucopyranosyl)-(1→'3)-4,6-O-benzylidene-2-deoxy-2-phthalimido-β-D-glucopyranoside (14) were prepared.     

Microstructural order in the developing cotton fiber based on availabilities of hydroxyl groups

The relative availabilities of accessible O(2)H, O(3)H, and O(6)H in the cellulose of developing cotton fibers were measured by conducting a reaction to a low degree of substitution under mild conditions in an aqueous medium. Raw cotton fibers from unopened bolls and from mature, opened bolls were studied. Correction was made for the presence of a β-1,3-glucan that was detected by substitution at the abundant O(4)H of this polysaccharide. The order of decreasing availability of hydroxyl groups of cellulose was O(2)H > O(6)H > > O(3)H. Results indicate that cellulose in the secondary wall of the cotton fiber is laid down with a high degree of order and that this order decreases with opening of the boll.     

New Triterpene Saponins from Herniaria glabra

Three new saponins 1–3 were isolated from Herniaria glabra by means of prep. HPLC and TLC. The structures were established mainly by a combination of 2D-NMR techniques (COSY, TOCSY, ROESY, HMQC, and HMBC) as O-α-L -rhamnopyranosyl-(1→4)-O-β-D -glucopyranosyl-(1-→6)-O-[β-D -glucopyranosyl-(1→2)]-β-D -glucopyranosyl medicagen-28-ate (herniaria saponin 4; 1 ), O-β-D -glucopyranosyl-(1→3)-O-α-L -rhamnopyranosyl-(1→2)-O-[β-(3R)-D -apiofuranosyl-(1→3)]-β-D -4-O-acetylfucopyranosyl 3-O-(β-D -glucuronopyranosyl)-16α-hydroxymedicagen-28-ate (herniaria saponin 5; 2 ), and O-α-L -rhamnopyranosyl-(1→4)-O-β-D -glucopyranosyl-(1→6)-O-[β-D -6-O-acetylglucopyra nosyl-(1→2)]-β-D -glucopyranosyl medicagen-28-ate (herniaria saponin 6; 3 ).     

Novel Reaction Route Including Enzymic Reaction For A Synthesis Of A Branched Polysaccharide

Abstract

Stereoselective synthesis of α-D-glucosyl-branching polysaccharide by chemical and enzymic reactions was investigated. Ring-opening polymerization of 1,6-anhydro-3-O-benzoyl-2,4-di-O-benzyl-β-D-glucopyranose (1) with PF₅ as catalyst at low temperature gave a highly stereoregular polymer, which was converted to 2,4-diO-benzyl-(1→6)-α-D-glucopyranan by debenzoylation with sodium methoxide. The polymer was glucosylated according to the glycosyl imidate method. Deprotection of the branched polysaccharide was carried out with sodium in liquid ammonia at -78 °C to give a (1→6)-α-D-glucopyranan having α-D-glucopyranosyl and β-D-glucopyranosyl branches. Only the β-D-glucopyranosyl branch of the polymer was completely removed by enzymatic hydrolysis by the use of cellulase to provide stereoregular (1→6)-α-D-glucopyranan having an α-D-glucopyranosyl branch at the C-3 position. Polymers were characterized by optical rotation, NMR spectroscopy, GPC, and X-ray diffractometry.     

Disposition of D-glucopyranosyl units on the surfaces of crystalline elementary fibrils of cotton cellulose

The results from two different chemical approaches to study the disposition of D -glucopyranosyl segments of the cellulose chains on the surfaces of microstructural units accessible to chemical reagents in cotton cellulose are compared, correlated, and rationalized. These studies provide the basis for a suggested disposition of D -glucopyranosyl units in the crystalline surfaces of elementary fibrils, for a proposed arrangement of hydrogen bonds on these surfaces, and for estimates of the size of the elementary fibrils.     

Synthesis of novel glycopeptide-polyoxazoline block copolymers by direct coupling between living anionic and cationic polymerization systems

A novel glycopeptide-containing block copolymer, poly[O-(tetra-O-acetyl-β-D -glucopyranosyl)-L -serine]-block-poly(2-methyl-2-oxazoline) ( 5 ), was synthesized by mutual termination of living polymerizations of a sugar-substituted α-amino acid N-carboxyanhydride (NCA) ( 1 ) and 2-methyl-2-oxazoline ( 3 ). 5 was deacetylated to provide the glycopeptide-polyoxazoline block copolymer, poly[O-(β-D -glucopyranosyl)-L -serine]-block-poly(2-methyl-2-oxazoline) ( 6 ).     

Lebbeckoside C,a new triterpenoid saponin from the stem barks of Albizia lebbeck inhibits the growth of human glioblastoma cells

One new acacic acid-type saponin, named lebbeckoside C (1), was isolated from the stem barks of Albizia lebbeck. Its structure was established on the basis of extensive analysis of 1D and 2D NMR (¹H, ¹³C NMR, DEPT, COSY, TOCSY, ROESY, HSQC and HMBC) experiments, HRESIMS studies, and by chemical evidence as 3-O-[β-d-xylopyranosyl-(l→2)-β-d-fucopyranosyl-(1→6)-[β-d-glucopyranosyl(1→2)]-β-d-glucopyranosyl]-21-O-{(2E,6S)-6-O-{4-O-[(2E,6S)-2,6-dimethyl-6-O-(β-d-quinovopyranosyl)octa-2,7-dienoyl]-4-O-[(2E,6S)-2,6-dimethyl-6-O-(β-d-quinovopyranosyl)octa-2,7-dienoyl]-β-d-quinovopyranosyl}-2,6-dimethylocta-2,7-dienoyl}acacic acid 28 O-[β-d-quinovopyranosyl-(l→3)-[α-l-arabinofuranosyl-(l→4)]-α-l-rhamnopyranosyl-(l→2)-β-d-glucopyranosyl] ester. The isolated saponin (1) displayed significant cytotoxic activity against the human glioblastoma cell line U-87 MG and TG1 stem-like glioma cells isolated from a patient tumor with IC₅₀ values of 1.69 and 1.44 μM, respectively.     

短柄雪胆中的三萜葫芦素及其皂苷

从短柄雪胆的块根中分离得到了14个三萜葫芦素类化合物. 经波谱分析及化学方法鉴定了它们的结构, 其中有新化合物5个, 分别命名为短柄雪胆苷A～E (1～5), 以及肉花雪胆苷元A (6), 藤三七雪胆苷R8 (7), 肉花雪胆苷I (8), 肉花雪胆苷II (9), 肉花雪胆苷III (10), 雪胆甲素(11), 雪胆乙素(12), 雪胆甲素苷(13), 藤三七雪胆苷R1 (14)等9个已知化合物. 6是首次从自然界中得到的化合物.     

High-Yield Syntheses of Tetra-O-benzyl-α-D-glucopyranosyl bromide and Tetra-O-pivaloyl-α-D-glucopyranosyl bromide and their Advantage in the Koenigs-Knorr Reaction

Summary. Several improved approaches for the preparation of tetra-O-benzyl-α-D-glucopyranosyl bromide and tetra-O-pivaloyl-α-D-glucopyranosyl bromide are discussed. The importance of these compounds, which are useful glycosyl donors, was demonstrated by successful preparation of cholesteryl glucopyranosides in an almost neutral medium without the formation of orthoesters. In addition, accurate ¹H and ¹³C NMR resonance assignments of the synthesized cholesteryl glycosides were performed by 2D NMR spectroscopy.