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11.
Workman JA Garrido NP Sançon J Roberts E Wessel HP Sweeney JB 《Journal of the American Chemical Society》2005,127(4):1066-1067
The first examples of highly enantioselective [2,3]-sigmatropic rearrangements of acyclic allylic ammonium ylids are reported. Thus, a range of N-{2'-[(N'-allyl-N',N'-dialkyl)ammonium]}acetyl camphor sultams undergo rearrangement at 0 degrees C in DME solution with high diastereofacial control (up to 99:1 dr) to give allylglycines in generally high yield. The power of the method has been demonstrated in a rapid and efficient synthesis of (R)-allyl glycine. 相似文献
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Two symmetrical trehalose glycosyl ‘acceptors’ 4 and 6 were prepared and three of the unsymmetrical type, 8 , 10 , and 11 . Glucosylation of symmetrical ‘acceptor’ 4 gave a higher yield of trisaccharide (44%) than protect ve-group manipulation, namely via selective debenzylidenation 2 → 9 or monoacetylation 2 → 5 which proceeded in moderate yields (33–34%). A comparison of catalysts in the cis-glucosylation of trehalose ‘acceptor’ 10 with tetra-O-benzyl-β-D -glucopyranosyl fluoride 13 profiled triflic anhydride ((Tf)2O) as a new reactive promoter yielding 92% of trisaccharide 14 , deblocking gave the target saccharide α-D -glucopyranosyI-( 1 → 4 )-α,α-D -trehalose. 1H-NMR spectra of most compounds were analyzed extensively. The use of the ID TOCSY technique is advocated for its time efficiency, if needed supplemented by ROESY experiments. 相似文献
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For the purpose of rapid drug monitoring, methods have been developed for the determination of 2,8-dihydroxyadenine, allopurinol, oxypurinol, adenine, hypoxanthine, hippuric acid and xanthine in urine with and without sodium dodecyl sulfate as additive in sodium tetraborate running buffer. No sample preparation is necessary. 6-methylmercaptopurine and etofylline have been used as the internal standards. The limit of detection is 5 microM and the range of quantification stretches from 20 to 2000 microM. The capillary electrophoresis methods are simple, fast and robust. 相似文献
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Hans Peter Wessel Rudolf Minder Gerhard Englert 《Journal of carbohydrate chemistry》2013,32(8):1101-1115
Abstract α,β-(1→4)-Glucans were devised as models for heparan sulfate with the simplifying assumptions that carboxyl-reduction and sulfation of heparan sulfate does not decrease the SMC antiproliferative activity and that N-sulfates in glucosamines can be replaced by O-sulfates. The target oligo-saccharides were synthesized using maltosyl building blocks. Glycosylation of methyl 2,3,6,2′,3′,6′-hexa-O-benzyl-β-maltoside (1) with hepta-O-acetyl-α-maltosyl bromide (2) furnished tetrasaccharide 3 which was deprotected to α-D-Glc-(1→4)-β-D-Glc-(1→4)-α-D-Glc-(1→4)-β-D-Glc-(1→OCH3) (5) or, alternatively, converted to the tetrasaccharide glycosyl acceptor (8) with one free hydroxyl function (4?′-OH). Further glycosylation with glucosyl or maltosyl bromide followed by deblocking gave the pentasaccharide [β-D-Glc-(1→4)-α-D-Glc-(1→4)]2-β-D-Glc-(1→OCH3) (11) and hexasaccharide [α-D-Glc-(1→4)-β-D-Glc-(1→4)2-α-D-Glc-(1→4)-β-D-Glc-(1→OCH3) (14). The protected tetrasaccharide 3 and hexasaccharide 12 were fully characterized by 1H and 13C NMR spectroscopy. Assignments were possible using 1D TOCSY, T-ROESY, 1H,1H 2D COSY supplemented by 1H-detected one-bond and multiple-bond 1H,13C 2D COSY experiments. 相似文献
17.
Yanying Lu Tianyu Zhu Wessel van den Bergh Morgan Stefik Kevin Huang 《Angewandte Chemie (International ed. in English)》2020,59(39):17004-17011
Developing high capacity and stable cathodes is a key to successful commercialization of aqueous Zn‐ion batteries (ZIBs). Pure layered V2O5 has a high theoretical capacity (585 mAh g?1), but it suffers severe capacity decay. Pre‐inserting cations into V2O5 can substantially stabilize the performance, but at an expense of lowered capacity. Here we show that an atomic layer deposition derived V2O5 can be an excellent ZIB cathode with high capacity and exceptional cycle stability at once. We report a rapid in situ on‐site transformation of V2O5 atomic layers into Zn3V2O7(OH)2?2 H2O (ZVO) nanoflake clusters, also a known Zn‐ion and proton intercalatable material. High concentration of reactive sites, strong bonding to the conductive substrate, nanosized thickness and binder‐free composition facilitate ionic transport and promote the best utilization of the active material. We also provide new insights into the V2O5‐dissolution mechanisms for different Zn‐salt aqueous electrolytes and their implications to the cycle stability. 相似文献
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