Synthesis of symmetrical disulfides by reaction of fluorine-containing thiiranes with cyclic amines

Regioselective opening of the thiirane ring in fluorine-containing thioglycidyl ethers and [(perfluorobutyl) methyl]thiirane by the action of cyclic amines afforded 1,2-aminothiols which were oxidized in situ to symmetrical disulfides. The rate of formation of the latter depended on the amine basicity. According to the NMR data, the resulting disulfides were mixtures of erythro and threo diastereoisomers.     

Synthesis of biomimetic light-driven molecular switches via a cyclopropyl ring-opening/nitrilium ion ring-closing tandem reaction

A cyclopropyl ring-opening/nitrilium ion ring-closing tandem reaction has been conveniently used in an expeditious synthetic approach to light-driven Z/E molecular switches featuring an imine function conjugated to olefin groups that mimics natural protonated Schiff bases.     

Synthesis of polysubstituted 5-hydroxyhydantoins via ring-opening of isatins

A simple and efficient tandem reaction approach was developed for the synthesis of 5-hydroxyhydantoins from one-pot reaction of isatins, phthalic anhydride or succinic anhydride, and 1,3-dimethylurea (1,3-diethylurea). The products were gained through the ring-opening of isatins process. The advantages of this report are simple operation, mild reaction conditions, good yields and easily available raw materials. It was very important for us to obtain the intermediate product and that provided a solid basis for the correct interpretation of the reaction mechanism.     

Synthesis of hyperbranched carbohydrate polymers by ring-opening multibranching polymerization of anhydro sugar

The synthesis of novel hyperbranched carbohydrate polymers, prepared by the ring-opening multibranching polymerizations of anhydro and dianhydro sugars, is described. The hyperbranched carbohydrate polymers were formed by the cationic polymerization of 1,6-anhydro-beta-D-hexopyranose, 1,4-anhydrotetritol, 2,3-anhydrotetritol, and 1,2:5,6-dianhydro-D-mannitol. These polymerizations proceeded without gelation to produce water-soluble hyperbranched carbohydrate polymers with controlled molecular weights and narrow polydispersities. The values for the degree of branching of the polymers were in the range of 0.28-0.50. The polymerization method, which proceeds through a ring-opening reaction by a proton-transfer reaction mechanism, is a facile method leading to a spherical carbohydrate polymer with a high degree of branching.     

Synthesis of optically inactive cellulose via cationic ring-opening polymerization

Cellulose, which comprises D-glucose and L-glucose (D,L-cellulose), was synthesized from D-glucose (1D) and L-glucose (1L) via cationic ring-opening polymerization. Specifically, the ring-opening copolymerization of 3-O-benzyl-2,6-di-O-pivaloyl-β-D-glucopyranoside (2D) and 3-O-benzyl-2,6-di-O-pivaloyl-β-D-glucopyranoside (2L), synthesized from compounds 1D and 1L, respectively, in a 1:1 ratio, afforded 3-O-benzyl-2,6-di-O-β-D,L-glucopyranan (3DL) with a degree of polymerization (DPn) of 28.5 (Mw/Mn?=?1.90) in quantitative yield. The deprotection of compound 3DL and subsequent acetylation proceeded smoothly to afford acetylated compound 4DL with a DPn of 18.6 (Mw/Mn?=?2.08). The specific rotation of acetylated compound 4DL was?+?0.01°, suggesting that acetylated compound 4DL was optically inactive cellulose triacetate. Furthermore, before acetylation, compound 4DL was an optically inactive cellulose comprising an almost racemic mixture of D-glucose and L-glucose. Compound 4DL was an amorphous polymer. This is the first reported synthesis of optically inactive D,L-cellulose.

     

Synthesis of branched aminopolysaccharides by acid-catalyzed polymerization of sugar oxazoline monomer

Acid-catalyzed polymerization of a sugar oxazoline monomer 1b having two free hydroxy groups was carried out to produce a branched aminopolysaccharide 2b. The reaction proceeded via the stereoregular glycosylation through oxazoline ring-opening process, giving rise to 2b consisting of β-glycosidic linkages. The structure of 2b was determined by the ¹H NMR, ¹³C NMR, and IR spectra. The molecular weights determined by GPC measurements were 4200-6100. The degrees of branching were estimated by the ¹H NMR spectra of the products by the reaction of 2b with 3,5-dinitrobenzoyl chloride. Deprotection of 2b was carried out by the catalytic hydrogenation in the presence of 10% Pd-C to produce a free branched aminopolysaccharide.     

Synthesis of poly(arylene disulfide)-vermiculite nanocomposites via in situ ring-opening reaction of cyclic oligomers

An exfoliated poly(4,4^′-oxybis(benzene)disulfide) (POBDS)/vermiculite (VMT) nanocomposite was prepared by using cyclo(4,4^′-oxybis(benzene)disulfide) (COBDS) oligomers and cetyltrimethyl ammonium bromide exchanged VMT. The POBDS/VMT nanocomposites were fabricated in two steps. First, the COBDS oligomers were used to swell and exfoliate organo VMT to afford COBDS-VMT nanocomposite precursor. Subsequently, the exfoliated POBDS-VMT nanocomposite can be made via in situ and instant melt ring-opening polymerization of the COBDS-VMT nanocomposite precursor. High molecular weight POBDS polymer can be formed in a few minutes. The nano scale dispersion of VMT layers within POBDS polymer was confirmed by both the X-ray diffraction patterns and TEM examinations. This methodology provides a potential approach to synthesize high performance polymer nanocomposite.     

Synthesis and properties of benzyl-substituted thiiranes

The reaction of phenyl- and p-tolylmagnesium bromides, as well as di, tri, and tetramethylbenzene, with epichlorohydrin was used to synthesize the corresponding chlorohydrins, which were then converted to various benzyl-substituted oxiranes and thiiranes.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 598–602, May, 1988.     

Some linear and branched macromolecules by ring-opening polymerization

In the first part the ring-opening polymerization of some macrocyclic ether-acetals is briefly described. Of special interest are acetal polymers with functional groups, for instance C=C-double bonds. Appropriate unsaturated monomers and their polymerizability are discussed. The second part deals with the polymerization of oxazolines, substituted in 2- and/or 4-position. Branched polymers are obtained by copolymerization of 2-ethyl-2-oxazoline with 2-hexyl-2-oxazoline or 2-undecyl-2-oxazoline. The properties of the random copolymers and corresponding block copolymers are compared. By a “mixed mechanism technique” a block copolymer composed of a poly(tert -butyl methacrylate) block and a poly(phenyloxazoline) block was prepared. A new initiator system for the polymerization of oxazolines using alkyl chloroformates is introduced. The chloroformate of a trifunctional alcohol led to a three-arm star polymer. Telechelics with two chloroformate endgroups form ABA type block copolymers. Finally four chiral oxazolines are described and the influence of substitution in dioxolanes and oxazolines on the polymerizability is discussed.     

Synthesis and ring-opening polymerization of glycidyl ethylene phosphate with a formation of linear and branched polyphosphates

1. Download high-res image (98KB)
2. Download full-size image

     

Synthesis of conformationally constrained C-glycosyl alpha- and beta-amino acids and sugar-carbamino sugar hybrids via Diels-Alder reaction

[structure: see text] Sugar-derived dienes undergo Diels-Alder reactions with methyl alpha-nitro acrylate and ethyl beta-nitro acrylate to form the corresponding cycloadducts which have been converted into conformationally constrained C-glycosyl alpha- and beta-amino acids. Further, these beta-amino acids are converted into sugar-carbamino sugar hybrid molecules.     

Synthesis of enantiopure pyrrolidine-derived peptidomimetics and oligo-beta-peptides via nucleophilic ring-opening of beta-lactams

The synthesis of the two enantiomers of pyrrolidine-derived spiro beta-lactams by resolution with D- and L-Boc phenylalanine is described. The potential of these optically active spiro beta-lactams on the synthesis of peptidomimetics as analogues of melanostatin is evaluated. Theoretical studies of several models, at the Becke3LYP/6-31+G* level of theory, together with previous experimental evidences from our group, gathered by NMR, allow us to design structures that can efficiently mimic some biologically active peptide-type molecules. On the other hand, the spiro beta-lactams have shown their utility in the preparation of beta-peptides. As an example, a homo-tetra-beta-peptide was synthesized. This research will continue in the future in order to obtain higher peptides with potential biological activity.     

Synthesis of a branched chain aza-C-disaccharide via the cycloaddition of a chiral nitrone to an alkene, both sugar derivatives

A multistep synthesis of a protected aza-C-disaccharide derivative with a pyrrolidine ring as the azasugar component is described. The key step is a stereoselective cycloaddition reaction of a chiral nitrone derived from D-ribose and a sugar alkene derived from D-galactose. An intramolecular N-alkylation followed by a reductive cleavage of the isoxazolidine N-O bond, in one pot, gave the final product.     

Synthesis of branched polyisobutylenes via cationic copolymerization of p-chloromethylstyrene and isobutylene

Branched polyisobutylenes (PIBs) with relatively low dispersities (1.4–1.8) and benzylic halide functionalities are synthesized by self-condensing vinyl cationic copolymerization of p-chloromethylstyrene (p-CMS) and isobutylene (IB) coinitiated by TiCl₄. It is found that the [IB]/[p-CMS] feed ratio plays a crucial role for the initiating behavior of p-CMS: the initiation arising from p-CMS is suppressed at [IB]/[p-CMS] ≥17; in contrast, the pendant benzyl chloride moiety of p-CMS monomer in the formed copolymer chains can initiate branching reactions. The resulting branched PIBs are of a gradient composition as well as a gradual increase in branching density due to large disparity in reactivity ratios. This strategy is successfully employed to create branched PIBs with low to moderate molecular weights (M_n, 5 k–78 k Da) through controlling the monomer/initiator mole ratio. However, it is shown that this method failed to obtain branched PIBs with high M_n, bearing a complicated copolymerization mechanism.     

Straightforward synthesis of thiodisaccharides by ring-opening of sugar epoxides

3,4-Anhydro hexopyranosides have been prepared by diastereoselective epoxidation of derivatives of 2-propyl 3,4-dideoxy-alpha-D-erythro-hex-3-enopyranoside (5), selectively protected at HO-2 and HO-6. The allylic group at C-2, in 5 and derivatives, plays a critical role in the facial selectivity of the epoxidation reaction. Thus, the free HO-2 in 3 (the 6-O-acetyl derivative of 5) directs the attack of m-chloroperbenzoic acid from the more hindered alpha face of the molecule to give 2-propyl 6-O-acetyl-3,4-anhydro-alpha-D-allopyranoside (7) accompanied by the beta epoxide 6 as a very minor product. Reverse diastereoselectivity has been obtained when the HO-2 in 3 was substituted by a bulky tert-butyldimethylsilyl (TBS) group. In this case, the major isomer was the 2-O-TBS derivative of 6 (alpha-D-galacto configuration). The ring-opening of sugar epoxides by nucleophilic per-O-acetyl-1-thio-beta-D-glucopyranose (11) was employed as a convenient approach to the synthesis of (1-->3)- and (1-->4)-thiodisaccharides. For example, ring-opening of the oxirane 7 by 11 led to the expected regioisomeric per-O-acetyl thiodisaccharides beta-D-Glc-S-(1-->3)-4-thio-alpha-D-Glc-O-iPr (12) and beta-D-Glc-S-(1-->4)-4-thio-alpha-D-Gul-O-iPr (13). Regioselectivity in the construction of the (1-->4)-thioglycosidic linkage could be achieved by hindering C-3 of the 3,4-anhydro sugar with a bulky silyloxy group at the vicinal C-2. For instance, coupling of the 2-O-TBS derivative of 7 with 11 led regioselectively to the protected thiodisaccharide beta-D-Glc-S-(1-->4)-4-thio-alpha-D-Glc-O-iPr (27). The utility of the approach was demonstrated through the synthesis of sulfur-linked analogues of naturally occurring (laminarabiose and cellobiose) and non-natural disaccharides (i.e., beta-D-Glc-(1-->4)-alpha-D-Gul).