Direct, Mild, and Selective Synthesis of Unprotected Dialdo‐Glycosides

Angelin, Marcus; Hermansson, Magnus; Dong, Hai; Ramström, Olof

doi:10.1002/ejoc.200600288

Cited by 58 publications

(27 citation statements)

References 26 publications

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“…The absence of TEMPO EPR signal was due to the oxidation of TEMPO by highly oxidizing species in Tris-treated PSII membranes. It is well known that under highly oxidizing conditions TEMPO is easily oxidized to oxoammonium salt [51]. To prevent the oxidation of paramagnetic TEMPO by highly oxidizing species formed on the PSII electron donor side, the spin-trapping was accomplished by utilizing the oxidation of hydrophilic diamagnetic 2, 2, 6, 6-tetramethyl-4-piperidone (TMPD) by 1 O 2 which yields paramagnetic 2, 2, 6, 6-tetramethyl-4-piperidone-1-oxyl (TEMPONE) (Fig.…”

Section: Resultsmentioning

confidence: 99%

Evidence on the Formation of Singlet Oxygen in the Donor Side Photoinhibition of Photosystem II: EPR Spin-Trapping Study

Yadav¹,

Pospı́šil

2012

PLoS ONE

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When photosystem II (PSII) is exposed to excess light, singlet oxygen (1O2) formed by the interaction of molecular oxygen with triplet chlorophyll. Triplet chlorophyll is formed by the charge recombination of triplet radical pair 3[P680•+Pheo•−] in the acceptor-side photoinhibition of PSII. Here, we provide evidence on the formation of 1O2 in the donor side photoinhibition of PSII. Light-induced 1O2 production in Tris-treated PSII membranes was studied by electron paramagnetic resonance (EPR) spin-trapping spectroscopy, as monitored by TEMPONE EPR signal. Light-induced formation of carbon-centered radicals (R•) was observed by POBN-R adduct EPR signal. Increased oxidation of organic molecules at high pH enhanced the formation of TEMPONE and POBN-R adduct EPR signals in Tris-treated PSII membranes. Interestingly, the scavenging of R• by propyl gallate significantly suppressed 1O2. Based on our results, it is concluded that 1O2 formation correlates with R• formation on the donor side of PSII due to oxidation of organic molecules (lipids and proteins) by long-lived P680•+/TyrZ•. It is proposed here that the Russell mechanism for the recombination of two peroxyl radicals formed by the interaction of R• with molecular oxygen is a plausible mechanism for 1O2 formation in the donor side photoinhibition of PSII.

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Section: Resultsmentioning

confidence: 99%

Evidence on the Formation of Singlet Oxygen in the Donor Side Photoinhibition of Photosystem II: EPR Spin-Trapping Study

Yadav¹,

Pospı́šil

2012

PLoS ONE

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“…A mild oxidant, TEMPOBF 4 , was effective to suppress the epimerization (entry 3). By using strong oxidant, TCCA, [ 35 ] a faster reaction occurred and the ratio was improved to 4/1 albeit with a low isolated yield (entry 4). We then focused on TEMPO‐derivatives.…”

Section: Resultsmentioning

confidence: 99%

A Modular Synthesis of Antitumor Macrolide (–)‐Lasonolide A^†

et al. 2020

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Summary of main observation and conclusion Lasonolide A was identified as a potent antitumor macrolide towards various cancer cell lines. The two tetrahydropyrans bearing multiple stereogenic centers as well as the polyene linkage attracted a dozen synthetic research groups to launch the total synthesis. Based on the synthetic methods developed in our group, namely, the hydroboration of allene and its subsequent allylation as well as the iterative hydroboration of allene and oxidation, the polyol subunits were efficiently constructed and then integrated into the final target. A new Julia olefination reagent, double‐headed sulfone, was designed to promote the rapid coupling of two aldehydes bearing multiple functional groups to secure the whole carbon framework. Another highlight of our approach is the application of a traceless protecting group, 9‐BBN (9‐borabicyclo[3.3.1]nonane), to hide the secondary alcohol for debenzylation, and for the first time, to mask the carboxylic acid for Julia olefination under strong basic conditions.

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“…However, for challenging carbohydrate substrates, complex product mixtures and overoxidation have been reported. [1b] Later, Ramström and co‐workers developed a method utilizing trichloroisocyanuric acid (TCICA) as the stoichiometric oxidant in DMF, buffered with NaHCO 3 , for the TEMPO‐catalyzed selective oxidation of the primary C ‐6‐OH function of unprotected glycosides . For the synthesis of bradyrhizose A (Figure ), Yu and co‐workers,[2b] and later Lowary and co‐workers,[2d] employed a slightly modified TEMPO‐catalyzed method (TEMPO/TCICA in CH 2 Cl 2 , no buffer) for the selective primary alcohol oxidation.…”

Section: Resultsmentioning

confidence: 99%

“…Likewise, in our case, the transformation of (7 S ,8 S )‐4 required meticulous optimization. Application of Ramström's conditions (cat. TEMPO, TCICA, NaHCO 3 in DMF) for the reaction of (7 S ,8 S )‐4 provided spiro‐ribofuranose 6 by direct hemiacetal formation of the intermediary aldehyde in an unclean manner and in only mediocre yields (44 %).…”

Section: Resultsmentioning

confidence: 99%

Synthetic Adventures with 2‐C‐Branched Carbohydrates: 4‐C‐Formyl Branched Octoses with Structural Analogy to Bradyrhizose

2019

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The synthesis of three 4‐C‐formyl branched octoses with variable stereoconfiguration at the C‐2 and C‐3 stereogenic centers is described. This class of compounds is of interest due to potential structural analogies to the naturally occurring bradyrhizose monosaccharide. Branched key sugar intermediates of the synthesis are 2‐C‐(1,2,3‐trihydroxyprop‐1‐yl)‐β‐d‐mannosides. A new mild oxidation protocol using known TEMPO/trichloroisocyanuric acid in ethyl acetate/toluene, buffered with 3‐(N‐morpholino)propanesulfonic acid, is described as a valuable reaction for selective primary alcohol oxidation and, hence, the formation of 2‐(spirofuranose)pyranoses. Upon global deprotection these spirofuranoses give complex mixtures of diverse hemiacetal forms of the liberated 4‐C‐formyl octoses. As revealed by detailed NMR studies, the bradyrhizose‐type annulated forms do not represent the major isomers. For each of the target octoses, these potential neighboured acetal‐hemiacetal‐forms (9,7‐pyranose‐1,9‐pyranoses) seem to be unfavorable, and instead remote bis(hemiacetals) are formed (1,5‐pyranose‐9,7‐pyranoses or 1,4‐furanose‐9,7‐pyranoses) as the major species.

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Direct, Mild, and Selective Synthesis of Unprotected Dialdo‐Glycosides

Cited by 58 publications

References 26 publications

Evidence on the Formation of Singlet Oxygen in the Donor Side Photoinhibition of Photosystem II: EPR Spin-Trapping Study

Evidence on the Formation of Singlet Oxygen in the Donor Side Photoinhibition of Photosystem II: EPR Spin-Trapping Study

A Modular Synthesis of Antitumor Macrolide (–)‐Lasonolide A^†

Synthetic Adventures with 2‐C‐Branched Carbohydrates: 4‐C‐Formyl Branched Octoses with Structural Analogy to Bradyrhizose

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Direct, Mild, and Selective Synthesis of Unprotected Dialdo‐Glycosides

Cited by 58 publications

References 26 publications

Evidence on the Formation of Singlet Oxygen in the Donor Side Photoinhibition of Photosystem II: EPR Spin-Trapping Study

Evidence on the Formation of Singlet Oxygen in the Donor Side Photoinhibition of Photosystem II: EPR Spin-Trapping Study

A Modular Synthesis of Antitumor Macrolide (–)‐Lasonolide A†

Synthetic Adventures with 2‐C‐Branched Carbohydrates: 4‐C‐Formyl Branched Octoses with Structural Analogy to Bradyrhizose

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A Modular Synthesis of Antitumor Macrolide (–)‐Lasonolide A^†