ChemInform Abstract: REGIOSELECTIVE HYDROGENOLYSIS OF 4,6‐O‐BENZYLIDENE DERIVATIVES OF HEXOPYRANOSIDES. PREPARATION OF “GLYVENOL”‐LIKE COMPOUNDS

Lipták, András; Pekar, F.; Jánossy, Lóránt; Jodál, I.; Fuegedi, P.; Harangi, János; Nánási, Pál; Szejtli, J.

doi:10.1002/chin.197929345

Cited by 3 publications

(4 citation statements)

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“…A known phenyl 4,6‐O‐benzylidene‐1‐thio‐β‐ d ‐glucopyranoside 7 [19] was selectively benzoylated (method A ) to give a mixture of 3‐ O ‐ and 2‐ O ‐benzoylated derivatives 8 [20] and 9 (63 %), the ratio of 8 : 9 was 7 : 1 according to NMR data. The mixture of 8 + 9 was silylated (method B ) to afford a mixture of 1 + 10 followed by removal of 4,6‐ O ‐benzylidene group under acidic conditions (method D ) to give diols 13 (63 %) and 14 (13 %).…”

Section: Resultsmentioning

confidence: 99%

Stereocontrolling Effect of a Single Triisopropylsilyl Group in 1,2‐cis‐Glucosylation

et al. 2022

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Glycosylation with phenyl 3,4,6-tri-O-benzoyl-2-O-triisopropylsilyl (TIPS)-1-thio-β-d-glucopyranoside is highly 1,2-cis-stereoselective, while the use of 2,3-di-O-TIPS glucosyl donor with benzoyl groups at O-4 and O-6 results in the loss of α-stereoselectivity (α/β = 3 : 1). Complete α-stereocontrol with 2-O-TIPS substituted glucosyl donors could only be achieved in glucosylation of weak nucleophiles. In this case, the glucosylation seems to proceed along the S N 1-like pathway via the 4 H 3 conformer of glycosyl cation stabilized by the bulky TIPS group at O-2.

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Section: Resultsmentioning

confidence: 99%

Stereocontrolling Effect of a Single Triisopropylsilyl Group in 1,2‐cis‐Glucosylation

et al. 2022

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“…The reductive cleavage of benzylidine acetal to form primary or seconday alcohols was achieved using a variety of reducing agents. These include [LiAlH 4 −AlCl 3 ], 152 , 153 [DIBAL-H], 154 − 156 [NaBH 3 CN-HCl], 158 − 160 [CF 3 COOH-Et 3 SiH],( 160 ) [BF 3 .OEt 2 -Et 3 SiH],( 161 ) and others. 162 − 171 An important alternative is oxidative cleavage using NBS in CCl 4 to give regioselectively benzoylated derivatives.…”

Section: Strategies Toward Modeling Starch Features: the Bottom-up Apmentioning

confidence: 99%

First Principles Insight into the α-Glucan Structures of Starch: Their Synthesis, Conformation, and Hydration

et al. 2010

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“…To a stirred solution of 1 19 A vigorously stirred solution of 2 (8.38 g, 19.5 mmol) in THF (24 ml) was added dropwise to a mixture of 50% aq KOH (40 mL), bis(2-chloroethyl)ether (40 mL, 0.34 mol) and catalytic amounts of tetrabutylammonium hydrogen sulfate. The mixture was stirred for 4-5 h at 50°C (TLC control) and then allowed to stand overnight at r.t. After neutralization with 50% aq AcOH and addition of H 2 O (50 mL), the product was extracted with CHCl 3 (3 × 100 mL).…”

Section: Phenyl 23-di-o-allyl-6-o-benzyl-b-d-glucopyranoside (2)mentioning

confidence: 99%

“…The allylation procedure generating the 2,3-di-O-allyl derivative 11 from phenyl 4,6-O-benzylidene-b-D-galactopyranoside (10) 11 is similar to those reported in the literature. 18,19 The reductive benzylidene acetal opening of 11 to the benzyl derivative 12 required a longer reaction time (48 h) than the benzylidene acetal opening of the glucose derivative 1. Furthermore, it is accompanied by a relatively unfavourable product ratio of 6-O-benzyl regioisomer 12 to phenyl 2,3-di-O-allyl-4-O-benzyl-b-Dgalactopyranoside (about 1:1).…”

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confidence: 99%

Synthesis of Carbohydrate-based Chiral Crown Ethers as Ligands in Asymmetric Hydrogenation

Faltin¹,

Fehring²,

Kadyrov³

et al. 2001

Synthesis

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Starting from phenyl 2,3-di-O-allyl-4,6-O-benzylideneb-D-glucopyranoside (1) the chiral crown ethers 6 and 7, containing a 1,4-bridged a-D-glucopyranoside moiety, were synthesized in four steps via phenyl 2,3-O-allyl-6-O-benzyl-b-D-glucopyranoside (2). To build up the corresponding polyethylene glycol side chain at 4-position, compound 2 was subsequently alkoxylated with bis(2-chloroethyl)ether and diethylene glycol or triethylene glycol yielding via 3 the polyethylene glycol derivatives 4 and 5, respectively. On a similar way phenyl 2, (15) was prepared from phenyl 4,6-O-benzylidene-b-D-galactopyranoside (10) via the intermediates 11, 12 and 13. The chiral crowns 6, 7, and 16 were obtained in yields of 26-38% by intramolecular transglycosylation of 4, 5, and 15, respectively. Whereas a high a-stereoselectivity was found for the cyclization of the 1,4-bridged D-glucose crowns 6 and 7, galactose derivative 15 gave the b-glycosidic linked crown 16. In order to obtain the rhodium chelates 18 and 20 as precatalysts for asymmetric hydrogenations, the gluco-crown ethers 6 and 7 were deallylated to 8 and 9 and phosphorylated under anaerobic conditions giving the bis(phosphinic esters) 17 and 19. The latter were used as ligands for 18 and 20. Finally, asymmetric hydrogenations of amino acid precursors 21a-d were investigated in the presence of the rhodium chelates 18 and 20. Under hydrogen, they show as catalysts in different solvents a diminished range of enantioselectivity in comparison with an analogous complex without such a crown ether ring. This can be explained by a stiffening effect of the anellated ring on the chelate ring conformation which is confirmed by the unusually uniform CD-spectra of 20 in solvents of different polarity.Carbohydrate-based chiral crown ethers find increasing interest in asymmetric organic synthesis. 1-10 Therefore, these compounds should be useful tools for the separation of enantiomers, chiral recognition in enzymatic reactions, and for the control of asymmetric syntheses. However, only a few of them proved to be effective in enantioselective reactions. 2b,3b,4,5,7c Rhodium(I) chelates of D-hexopyranoside-2,3-O-bisphosphinites are extremely useful in the asymmetric hydrogenation of amino acid precursors 11 and have even found application in the industrial production of L-DOPA. 12 Our aim was to synthesize analogous catalysts containing an anellated crown ether-like ring in the 1,4-position of the carbohydrate. Since it is well known that solvent polarity and the formation of cryptate species with alkali ions strongly influence the conformation of crown ethers, 13 we wanted to investigate whether the tuning of these effects would increase the enantioselectivity of these new catalysts. More detailed background information on asymmetric hydrogenation can be found in the latest review by Brown. 14 Based on a strategy reported before, 8 the 17-membered and 20-membered macrocyclic compounds 6 and 7, were synthesized in four steps according to Scheme 1. At first, the benzylidene acetal of p...

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ChemInform Abstract: REGIOSELECTIVE HYDROGENOLYSIS OF 4,6‐O‐BENZYLIDENE DERIVATIVES OF HEXOPYRANOSIDES. PREPARATION OF “GLYVENOL”‐LIKE COMPOUNDS

Abstract: Hydrogenolyse der alkylierten Glucopyranoside (I) bzw. (III) [erhältlich durch 2,3‐Di‐O‐alkylierung der entsprechenden Glucopyranoside] mit Li‐alanat/AlCl3 liefert die 4‐O‐Benzyl‐Derivate (II) bzw. (IV), die pharmakologisch getestet werden sollen.

Cited by 3 publications

References 0 publications

Stereocontrolling Effect of a Single Triisopropylsilyl Group in 1,2‐cis‐Glucosylation

Stereocontrolling Effect of a Single Triisopropylsilyl Group in 1,2‐cis‐Glucosylation

First Principles Insight into the α-Glucan Structures of Starch: Their Synthesis, Conformation, and Hydration

Synthesis of Carbohydrate-based Chiral Crown Ethers as Ligands in Asymmetric Hydrogenation

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