The Experts below are selected from a list of 288 Experts worldwide ranked by ideXlab platform
Ian Milligan - One of the best experts on this subject based on the ideXlab platform.
-
Complete Depolymerization and Repolymerization of a Sugar Poly(orthoester)
ChemSusChem, 2017Co-Authors: Sampa Maiti, Nicole A. Thompson, Ian MilliganAbstract:The capability of a polymer to depolymerize, regenerating its original monomer for further polymerization, is very attractive in terms of sustainability. Recently discovered sugar poly(Orthoesters) are an important class of glycopolymer. The high sensitivity of the backbone orthoester linkage toward acidolysis provides a valuable model to study the depolymerization. Herein, a sugar poly(orthoester) is shown to be completely depolymerized under acidic conditions. Interestingly, instead of the original monomer, the depolymerization gave a stable cyclic product (1,6-anhydro glucopyranose) in most cases, which was kinetically and thermodynamically favored. However, this pathway could be inhibited by chemically deactivating a key intermediate and thus favoring the formation of the original monomer. Efficient repolymerizaton of the regenerated monomer is also demonstrated.
-
Syntheses of sugar poly(Orthoesters) through reverse anomeric effect.
Chemical communications (Cambridge England), 2015Co-Authors: Jun Wang, Ian Milligan, Melissa Obrinske, Kylie O'hara, Lindsay BittermanAbstract:High molecular weight sugar poly(Orthoesters) were synthesized through reverse anomeric effect (RAE). We demonstrated that when RAE-enabled promoters, such as 4-(dimethylamino)pyridine (DMAP), triphenylphosphine (TPP) or imidazole, were employed, efficient polymerizations were achieved, giving sugar poly(Orthoesters) with molecular weights up to 18 kDa.
-
Synthesis of Highly pH‐Responsive Glucose Poly(orthoester)
Angewandte Chemie (International ed. in English), 2013Co-Authors: Ian Milligan, Emily A. FranckowiakAbstract:pH-Responsive polymers have great potential in biomedical applications, including the selective delivery of preloaded drugs to tissues with low pH values. These polymers usually contain acid-labile linkages such as esters and acetals/ketals. However, these linkages are only mildly pH-responsive with relatively long half-lives (t1/2). Orthoester linkages are more acid-labile, but current methods suffer from synthetic challenges and are limited to the availability of monomers. To address these limitations, a sugar poly(orthoester) was synthesized as a highly pH-responsive polymer. The synthesis was achieved by using 2,3,4-tri-O-acetyl-α-D-glucopyranosyl bromide as a difunctional AB monomer and tetra-n-butylammonium iodide (TBAI) as an effective promoter. Under optimal conditions, polymers with molecular weights of 6.9 kDa were synthesized in a polycondensation manner. The synthesized glucose poly(orthoester), wherein all sugar units were connected through orthoester linkages, was highly pH-responsive with a half-life of 0.9, 0.6, and 0.2 hours at pH 6, 5, and 4, respectively.
Srinivas Hotha - One of the best experts on this subject based on the ideXlab platform.
-
Propargyl 1,2-Orthoesters for a catalytic and stereoselective synthesis of pyrimidine nucleosides.
The Journal of organic chemistry, 2015Co-Authors: Boddu Venkateswara Rao, Sujit Manmode, Srinivas HothaAbstract:Pyrimidine nucleosides are synthesized by using propargyl 1,2-Orthoesters and Au(III) salt as a catalyst. Strategically positioned 1,2-Orthoesters are found to yield only 1,2-trans nucleosides and enable preparation of 2′-OH containing pyrimidine nucleosides. The glycosyl donor employed in this study is stable and easily accessible. The identified high-yielding protocol is mild, diastereoselective, and catalytic.
-
Propargyl 1,2-Orthoesters for a Catalytic and Stereoselective Synthesis of Pyrimidine Nucleosides
2015Co-Authors: Boddu Venkateswara Rao, Sujit Manmode, Srinivas HothaAbstract:Pyrimidine nucleosides are synthesized by using propargyl 1,2-Orthoesters and Au(III) salt as a catalyst. Strategically positioned 1,2-Orthoesters are found to yield only 1,2-trans nucleosides and enable preparation of 2′-OH containing pyrimidine nucleosides. The glycosyl donor employed in this study is stable and easily accessible. The identified high-yielding protocol is mild, diastereoselective, and catalytic
-
Facile synthesis of unusual glycosyl carbamates and amino acid glycosides from propargyl 1,2-Orthoesters as glycosyl donors.
Organic & biomolecular chemistry, 2011Co-Authors: Ashif Y. Shaikh, Gopalsamy Sureshkumar, Debasis Pati, Sayam Sen Gupta, Srinivas HothaAbstract:Propargyl 1,2-O-Orthoesters are exploited for the synthesis of 1,2-trans O-glycosides of protected amino acids. N-Fmoc- and N-Cbz protected serine/threonine - benzyl/methyl esters reacted well with glucosyl-, galactosyl-, mannosyl- and lactosyl- derived propargyl 1,2-Orthoesters affording respective 1,2-transglycosides in good yields under AuBr3/4 A MS Powder/CH2Cl2/rt. t-Boc serine derivative gave serine 1,2-orthoester and glycosyl carbamate. Optimized conditions enabled preparation of new glycosyl carbamates from N-Boc protected amines in a single step using gold catalysts and propargyl 1,2-Orthoesters in excellent yields.
-
Orthogonal activation of propargyl and n-pentenyl glycosides and 1,2-Orthoesters.
The Journal of organic chemistry, 2009Co-Authors: Srinivasa Rao Vidadala, Shivaji A. Thadke, Srinivas HothaAbstract:An orthogonal activation strategy with propargyl and n-pentenyl glycosides has been identified. According to this methodology, n-pentenyl glycosides can be selectively activated with NIS/TMSOTf in the presence of either armed or disarmed propargyl O-glycosides. In addition, we report herein that propargyl 1,2-Orthoesters can be selectively activated with AuBr 3 in CH 2 Cl 2 at room temperature in the presence of n-pentenyl glycosides. Similarly, pentenyl 1,2-Orthoesters can be selectively activated with NIS/Yb(OTf) 3 in the presence of propargyl glycosides.
-
Gold mediated glycosylations: selective activation of propargyl 1,2-Orthoesters in the presence of aglycones containing a propargyl moiety
Chemical communications (Cambridge England), 2008Co-Authors: Gopalsamy Sureshkumar, Srinivas HothaAbstract:Selective activation of propargyl 1,2-Orthoesters in the presence of propargyl glycosides and propargyl ethers was studied; a catalytic amount of AuBr3 activated the propargyloxy group of the 1,2-orthoester thereby giving access to disaccharides with the propargyl group at the reducing end; furthermore, propargyl ethers were unaffected under the reaction conditions.
Takeshi Endo - One of the best experts on this subject based on the ideXlab platform.
-
Copolymers containing a spiro orthoester moiety that undergo no shrinkage during cationic crosslinking
Journal of Polymer Science Part A: Polymer Chemistry, 2006Co-Authors: Makoto Kume, Atsunori Hirano, Bungo Ochiai, Takeshi EndoAbstract:A spiro orthoester with an exomethylene group (exoSOE) was radically copolymerized with acrylonitrile or vinyl acetate at several feed ratios to obtain the corresponding copolymers having spiro orthoester moieties in the side chain. The obtained copolymers could be crosslinked via the double ring-opening polymerization of the spiro orthoester moieties in their side chain by a treatment with BF 3 OEt 2 . The volume changes upon the crosslinking of the copolymers were evaluated by density measurements with a micromeritics gas pycnometer. The copolymers experienced less than 1% volume expansion instead of volume shrinkage during typical cationic crosslinking, regardless of the copolymer compositions. Negligible shrinkage was observed during the thermal cationic crosslinking of a film cast from a nitrobenzene solution of the copolymers containing a benzylthiophenium salt as a thermally latent cationic initiator. The constantly low volume changes during the crosslinking of the copolymers from exoSOE probably depended on the almost zero volume change during the cationic polymerizations of spiro orthoester derivatives. This indicates that exoSOE is an effective monomer for crosslinkable polymers without volume changes.
-
Synthesis and cationic ring-opening polymerization of mono- and bifunctional spiro Orthoesters containing ester groups and depolymerization of the obtained polymers : An approach to chemical recycling for polyesters as a model system
Journal of Polymer Science Part A: Polymer Chemistry, 1999Co-Authors: Kiyoko Yoshida, Fumio Sanda, Takeshi EndoAbstract:A spiro orthoester having an ester moiety, 2-acetoxymethyl-1,4,6-trioxaspiro[4.6]undecane (4) was synthesized, and its cationic polymerization and depolymerization of the obtained polymer (5) were carried out. The monomer 4 underwent cationic polymerization with a cationic catalyst to afford the corresponding poly(cyclic orthoester) 5. The obtained polymer 5 could be depolymerized with a cationic catalyst to regenerate the monomer 4 in an excellent yield. Further, bifunctional spiro Orthoesters (6, 8, 9) having diester moieties were synthesized from terephthalic acid, succinic acid, and 1,4-cyclohexanedicarboxylic acid, and their acid-catalyzed reversible crosslinking–decrosslinking was examined. The bifunctional monomer 6 derived from terephthalic acid underwent cationic crosslinking to afford the corresponding network polymer (7), which could be also depolymerized to regenerate the original bifunctional monomer 6. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2551–2558, 1999
-
A novel approach for the chemical ‘recycling’ of polymeric materials equilibrium polymerization system of spiro Orthoesters
Reactive and Functional Polymers, 1997Co-Authors: Takeshi Endo, Fumio SandaAbstract:Abstract Crosslinked poly(cyclic orthoester)s prepared by radical additions of poly(cyclic orthoester)s possessing exomethylene groups and dithiols efficiently depolymerized to bifunctional spiro Orthoesters in the presence of trifluoroacetic acid in dichloromethane. Furthermore, the dithiol-linked bifunctional spiro orthoester monomers prepared by the radical additions of spiro orthoester possessing exomethylene group and dithiols afforded the corresponding crosslinked polymers in the presence of trifluoroacetic acid as a catalyst in bulk condition. The quantitative depolymerization of the obtained cross-linked polymer afforded the corresponding bifunctional monomer in dichloromethane at room temperature. Meanwhile, an acid-catalyzed reversible crosslinking-depolymerization of a polymer having a spiro orthoester group in the side chain was carried out. The copolymer obtained by the radical copolymerization of 2-methylene-1,4,6-trioxaspiro[4.6]undecane with acrylonitrile was treated with trifluoroacetic acid in dichloromethane at −10°C to afford the crosslinked polymer quantitatively. The crosslinked polymer was then treated with trifluoroacetic acid at a low concentration in dichloromethane at room temperature to recover the original polymer.
-
Synthesis and Reactions of exo-Methylene-Containing Poly(cyclic orthoester)
Macromolecules, 1994Co-Authors: Satoyuki Chikaoka, Toshikazu Takata, Takeshi EndoAbstract:Syntheses of poly(cyclic orthoester) bearing an exo-methylene group (4) by a polymer reaction of the corresponding bromomethyl derivative and radical additions of thiols to 4 were carried out. The exo-methylene-containing poly(cyclic orthoester) I was prepared in 71% yield by dehydrobromination with t-BuOK of bromomethyl-substituted poly(cyclic orthoester) which was synthesized by cationic single ring-opening polymerization of 2-(bromomethyl)-1,4,6-trioxaspiro[4.6]undecane (6) with SnCl 4 .
Wenbin Lin - One of the best experts on this subject based on the ideXlab platform.
-
Rearrangement of sugar 1,2-Orthoesters to glycosidic products: a mechanistic implication.
Carbohydrate research, 2000Co-Authors: Zunyi Yang, Wenbin LinAbstract:The identification of cross-over products in the rearrangement of two structurally similar sugar 1,2-Orthoesters to glycosidic products is reported.
Hucheng Zhu - One of the best experts on this subject based on the ideXlab platform.
-
(±)-PeniOrthoesters A and B, Two Pairs of Novel Spiro-Orthoester en-antiomers With an Unusual 1,4,6-Trioxaspi-ro[4.5]decane-7-One Unit From Penicillium minioluteum
Frontiers Media S.A., 2018Co-Authors: Xiaorui Liu, Chunmei Chen, Yinyu Zheng, Mi Zhang, Qingyi Tong, Junjun Liu, Qun Zhou, Jianping Wang, Zengwei Luo, Hucheng ZhuAbstract:(±)-PeniOrthoesters A and B (±1 and ±2), two pairs of unprecedented spiro-orthoester enantiomers with a 1,4,6-trioxaspiro[4. 5]decane-7-one unit, were obtained from Penicillium minioluteum. Their structures were determined by spectroscopic methods, X-ray diffraction analyses, and ECD calculations. (±)-PeniOrthoesters A and B are the first examples of spiro-orthoester enantiomers, and they represent the first spiro-Orthoesters originating from fungi. All compounds showed potential inhibitory activities comparable to dexamethasone against NO production with IC50 values ranging from 14.2 to 34.5 μM
-
Data_Sheet_1_(±)-PeniOrthoesters A and B, Two Pairs of Novel Spiro-Orthoester en-antiomers With an Unusual 1,4,6-Trioxaspi-ro[4.5]decane-7-One Unit From Penicillium minioluteum.PDF
2018Co-Authors: Xiaorui Liu, Chunmei Chen, Yinyu Zheng, Mi Zhang, Qingyi Tong, Junjun Liu, Qun Zhou, Jianping Wang, Zengwei Luo, Hucheng ZhuAbstract:(±)-PeniOrthoesters A and B (±1 and ±2), two pairs of unprecedented spiro-orthoester enantiomers with a 1,4,6-trioxaspiro[4. 5]decane-7-one unit, were obtained from Penicillium minioluteum. Their structures were determined by spectroscopic methods, X-ray diffraction analyses, and ECD calculations. (±)-PeniOrthoesters A and B are the first examples of spiro-orthoester enantiomers, and they represent the first spiro-Orthoesters originating from fungi. All compounds showed potential inhibitory activities comparable to dexamethasone against NO production with IC50 values ranging from 14.2 to 34.5 μM.
-
Table_1_(±)-PeniOrthoesters A and B, Two Pairs of Novel Spiro-Orthoester en-antiomers With an Unusual 1,4,6-Trioxaspi-ro[4.5]decane-7-One Unit From Penicillium minioluteum.DOC
2018Co-Authors: Xiaorui Liu, Chunmei Chen, Yinyu Zheng, Mi Zhang, Qingyi Tong, Junjun Liu, Qun Zhou, Jianping Wang, Zengwei Luo, Hucheng ZhuAbstract:(±)-PeniOrthoesters A and B (±1 and ±2), two pairs of unprecedented spiro-orthoester enantiomers with a 1,4,6-trioxaspiro[4. 5]decane-7-one unit, were obtained from Penicillium minioluteum. Their structures were determined by spectroscopic methods, X-ray diffraction analyses, and ECD calculations. (±)-PeniOrthoesters A and B are the first examples of spiro-orthoester enantiomers, and they represent the first spiro-Orthoesters originating from fungi. All compounds showed potential inhibitory activities comparable to dexamethasone against NO production with IC50 values ranging from 14.2 to 34.5 μM.