With the picolinyl (Pic) group as a C‐1 located directing group and N3 as versatile precursor for C5‐NH2, a novel 1‐Pic‐5‐N3 thiosialyl donor was designed and synthesized, based on which a new ...sialylation protocol was established. In comparison to conventional sialylation methods, the new protocol exhibited obvious advantages, including excellent α‐stereoselectivity in the absence of a solvent effect, broad substrate scope encompassing the challenging sialyl 8‐ and 9‐hydroxy groups of sialic acid acceptors, flexibility in sialoside derivative synthesis, high temperature tolerance and easy scalability. In particular, the applicability to the synthesis of complex and bioactive N‐glycan antennae when combined with the MPEP glycosylation protocol via the “latent‐active” strategy has been shown. Mechanistically, the excellent α‐stereoselectivity of the novel sialylation protocol could be attributed to the dramatic electron‐withdrawing effect of the protonated Pic groups, which was supported by control reactions and DFT calculations.
Sugar building blocks: With 1‐Picolinyl‐5‐azido thiosialoside as donor, a robust sialylation was developed that is applicable to the flexible synthesis of complex sialosides and shows broad substrate scope, good to excellent chemical yield, excellent α‐stereoselectivity, high temperature tolerance, and easy scalability.
An anaerobic/aerobic moving-bed biofilm (A/O-MBBR) reactor system was constructed, and the treatment efficiency of aqueous antibiotics in wastewater was investigated. The effects of antibiotics on ...the microbial communities in the A/O-MBBR were also investigated. Under the optimized reaction conditions, removal of tetracycline antibiotics (TCs) was studied in a series of experiments. When a low concentration of tetracycline (TC) was added to the reactor system, high removal efficiency of conventional pollutants (TC concentration decreased from 10 turn to 2.8 μg L
−1
) was achieved. When mixed TCs (50 μg L
−1
) were added to the system, the removal efficiencies of chlortetracycline (CTC), TC and oxytetracycline (OTC) reached 52.03, 41.79, and 38.42%, respectively. TC degradation was decreased to 21.16% when the antibiotic concentration was 500 μg L
−1
; exposure to this TC concentration destroyed the community structure of the activated sludge bacteria in the reactor. The products of the biodegradation analysis revealed the possible degradation pathways functioning in the experimental A/O-MBBRs.
The 2,2-dimethyl-2-(ortho-nitrophenyl)acetyl (DMNPA) group was introduced to synthetic carbohydrate chemistry as a protecting group (PG) for the first time. Benefiting from a unique chemical ...structure and novel deprotection conditions, the DMNPA group can be cleaved rapidly and mutually orthogonal to other PGs. Orchestrated application of the DMNPA group with other PGs led to the highly efficient synthesis of the glycan of thornasterside A.
A general and efficient method for the synthesis N‐difluoroethyl imides has been developed. This copper‐catalyzed four‐component reaction proceeds via in‐situ generated difluorodiazomethane, which ...does not require prior formation and transferring. The reaction is scalable, tolerant toward a range of functional groups, and also suitable for the late‐stage functionalization of drugs and drug‐like molecules.
A general and efficient copper‐catalyzed four‐component reaction for the synthesis N‐difluoroethyl imides that proceeds via in situ generated difluorodiazomethane, which does not require prior formation and transferring, is described. The reaction is scalable, tolerating a range of functional groups, and it is also suitable for the late‐stage functionalization of drugs and drug‐like molecules.
Based on the application of phase‐transfer‐catalysis and Yu glycosylations, the first total syntheses of the arylnaphthyl glycosides phyllanthusmin D and 4′′‐O‐acetylmananthoside B, which have been ...claimed to be ideal antitumoral lead compounds in terms of cytotoxicity, cytotoxic selectivity, and a new mechanism of action, were achieved. Starting from easily accessible compounds, the two target molecules were obtained with longest linear sequences of 9 and 15 steps, in overall yields of 29 and 9 %, respectively. As part of this synthetic investigation, an efficient and scalable synthetic route to diphyllin was established, and the atropisomeric phenomenon in the arylnaphthyl glycosides was also confirmed.
The first total syntheses of phyllanthusmin D and 4′′‐O‐acetylmananthoside B, which have been claimed to be ideal antitumoral lead compounds in terms of cytotoxicity and selectivity, were achieved. Starting from easily accessible compounds, the two target molecules were obtained with longest linear sequences of 9 and 15 steps, in overall yields of 29 and 9 %, respectively.
Based on the capability of silyl ethers for efficient glycosylation, the new MTEAN glycosylation protocol utilizing 8-methyltosylaminoethynyl-1-naphthyl (MTEAN) glycosides as donors were extended to ...one-pot synthesis of nucleosides, late-stage modification of bioactive molecules, and stereoselective construction of 1,2-cis-glucosidic linkages using silyl ethers of the acceptors. Moreover, the reaction mechanism was systematically investigated by control reactions and side product characterizations, leading to the determination of a TfOH-catalyzed ynamide functionality-initiated process, which was further corroborated by identifications of the departure form of leaving group and the real catalyst.
A novel alkyne-activation-based glycosylation protocol using o-(p-methoxyphenylethynyl)phenyl (MPEP) glycoside was established. The glycosyl MPEP donors were shelf-stable and could be prepared ...efficiently via Sonogashira reaction from the corresponding o-iodophenyl (IP) glycosides. The outstanding stability of IP glycosides as well as their efficient transformations to MPEP glycosides dramatically facilitates the syntheses of MPEP glycosyl donors and IP glycosyl acceptors. Furthermore, they make the MPEP glycosylation protocol applicable to the latent-active oligosaccharide and glycoconjugate synthetic strategy, with IP glycosides as the latent form and MPEP glycosides as the active form, as illustrated by the highly efficient fabrication of Streptococcus pneumoniae type 3 trisaccharide. The phenolic glycoside nature of MPEP glycosides bestows on the new glycosyl donors enhanced stability compared to their thioglycoside counterparts toward activation conditions applied for glycosyl trichloroacetimidate (TCAI) and o-alkynylbenzoate (ABz) donor. Thus, MPEPs can also be utilized in the selective one-pot glycosylation strategy, as exemplified by the syntheses of oligosaccharides via successive glycosylations with glycosyl TCAI, ABz, and EPMP as donors. Despite sharing identical promotion conditions with thioglycoside donors, the odor-free starting material (IP), the stable departure structure of the leaving group (3-iodobenzofuran), and the decreased nucleophilicity of the o-MPEP glycoside help to eliminate the three major shortcomings of the thioglycoside donors (unpleasant odor of starting material, detrimental interference of the cleaved leaving group, and aglycon intra- or intermolecular migration) while maintaining the prominent features of the thioglycoside methodology, including the broad substrate scopes, the mild promotion conditions, the stability of glycosyl donors, and the versatile applications in existing glycoside synthesis strategies. Based on the experimental results, a mechanism for MPEP activation was proposed, which was supported by systematic mechanistic investigations, including trapping of active intermediates, design of a vital disarmed rhamnosyl donor, and isolation and characterization of the departure species of the leaving group.
With glycosyl o-alkynylbenzotes as donors, a highly efficient protocol to construct the challenging glycosidic linkages at C3-OH of C23-oxo oleanane triterpenoids is disclosed, on the basis of which ...different strategies for the highly efficient synthesis of QS-21 analogues with the west-wing trisaccharide of QS-21 have been established.
Abstract
C
12
H
9
NO
4
S, triclinic, P1̅ (no. 2), a = 3.9201(5) Å, b = 11.836(2) Å, c = 13.105(2) Å, ɑ = 67.415(4)°, β = 83.375(4)°, γ = 82.156(4)°, V = 554.8 Å
3
, Z = 2, R
gt
(F) = 0.0401, wR
ref
...(F
2
) = 0.0999, T = 293 K.
C
S, monoclinic, Cc (no. 9), a = 28.720(3) Å, b = 6.1696(6) Å, c = 7.5796(8) Å, ( = 99.756(3)°, V = 1323.6 Å
, Z = 4, R
(F) = 0.0505, wR
(F
) = 0.1154, T = 273 K.
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