134,008 research outputs found
Synthesis of and a Comparative Study on the Inhibition of Muscle and Liver Glycogen Phosphorylases by Epimeric Pairs of d-Gluco- and d-Xylopyranosylidene-spiro-(thio)hydantoins and <i>N</i>-(d-Glucopyranosyl) Amides
No full textd-Gluco- and d-xylopyranosylidene-spiro-hydantoins and -thiohydantoins were prepared from
the parent sugars in a six-step, highly chemo-, regio-, and stereoselective procedure. In the
key step of the syntheses C-(1-bromo-1-deoxy-β-d-glycopyranosyl)formamides were reacted with
cyanate ion to give spiro-hydantoins with a retained configuration at the anomeric center as
the major products. On the other hand, thiocyanate ions gave spiro-thiohydantoins with an
inverted anomeric carbon as the only products. On the basis of radical inhibition studies, a
mechanistic rationale was proposed to explain this unique stereoselectivity and the formation
of C-(1-hydroxy-β-d-glycopyranosyl)formamides as byproducts. Enzyme assays with a and b
forms of muscle and liver glycogen phosphorylases showed spiro-hydantoin 12 and spiro-thiohydantoin 14 to be the best and equipotent inhibitors with Ki values in the low micromolar
range. The study of epimeric pairs of d-gluco and d-xylo configurated spiro-hydantoins and
N-(d-glucopyranosyl)amides corroborated the role of specific hydrogen bridges in binding the
inhibitors to the enzyme
Biocatalytic route to <i>C</i>-4′-spiro-oxetano-xylofuranosyl pyrimidine nucleosides
No full textA facile access to C-4′-spiro-oxetano-xylofuranosyl nucleosides has been demonstrated for the first time through Lipozyme® TL IM-mediated regioselective acetylation of one of the primary hydroxyl group over the other primary and secondary hydroxyl groups in 3′-O-benzyl-4′-C-hydroxymethyl-β-D-xylofuranosyl nucleosides. Attempts to optimize a convergent route for these spironucleosides via selective manipulation of hydroxyl groups in 3-O-benzyl-4-C-hydroxymethyl-1,2-O-isopropylidene-α-D-xylofuranose were unsuccessful. Nevertheless; the present linear biocatalytic route efficiently afforded the C-4′-spiro-oxetanoxylofuranosyl nucleosides T and U in 47 and 38% overall yields, respectively, starting from corresponding furanose diol.</p
Glucopyranosylidene-spiro-benzo[<i>b</i>][1,4]oxazinones and -benzo[<i>b</i>][1,4]thiazinones: Synthesis and Investigation of Their Effects on Glycogen Phosphorylase and Plant Growth Inhibition
No full textGlucopyranosylidene-spiro-benzo[b][1,4]oxazinones
were obtained via the corresponding 2-nitrophenyl glycosides obtained
by two methods: (a) AgOTf-promoted glycosylation of 2-nitrophenol
derivatives by O-perbenzoylated methyl (α-d-gluculopyranosyl bromide)heptonate or (b) Mitsunobu-type reactions
of O-perbenzoylated methyl (α-d-gluculopyranose)heptonate
with bulky 2-nitrophenols in the presence of diethyl azodicarboxylate
(DEAD) and PPh3. Catalytic hydrogenation (H2–Pd/C) or partial reduction (e.g., H2–Pd/C,
pyridine) of the 2-nitro groups led to spiro-benzo[b][1,4]oxazinones and spiro-benzo[b][1,4]-4-hydroxyoxazinones
by spontaneous ring closure of the intermediate 2-aminophenyl or 2-hydroxylamino
glycosides, respectively. The analogous 2-aminophenyl thioglycosides,
prepared by reactions of O-perbenzoylated methyl
(α-d-gluculopyranosyl bromide)heptonate with 2-aminothiophenols,
were cyclized in m-xylene at reflux temperature to
the corresponding spiro-benzo[b][1,4]thiazinones. O-Debenzoylation was effected by Zemplén transesterification
in both series. Spiro-configurations were determined by NMR and electronic
circular dichroism time-dependent density functional theory (ECD-TDDFT)
methods. Inhibition assays with rabbit muscle glycogen phosphorylase
b showed (1′R)-spiro{1′,5′-anhydro-d-glucitol-1′,2-benzo[b][1,4]oxazin-3(4H)-one} and (1′R)-spiro{1′,5′-anhydro-d-glucitol-1′,2-benzo[b][1,4]thiazin-3(4H)-one} to be the most efficient inhibitors (27 and 28%
inhibition at 625 μM, respectively). Plant growth tests with
white mustard and garden cress indicated no effect except for (1′R)-4-hydroxyspiro{1′,5′-anhydro-d-glucitol-1′,2-benzo[b][1,4]oxazin-3(4H)-one} with the latter plant to show modest inhibition
of germination (95% relative to control)
Spiro-Linked Ter-, Penta-, and Heptafluorenes as Novel Amorphous Materials for Blue Light Emission
No full textA series of spiro-linked oligofluorenes were synthesized that exhibit blue emission with
photoluminescence quantum yields in some cases exceeding 0.50 in neat spin-coated films.
Differential scanning calorimetry revealed highly variable glass transition temperatures. A
longer conjugation length is desired for better stability against thermally activated
crystallization, and a shorter pendant is desired for a higher glass transition temperature
at a given conjugation length. In contrast to poly(2,7-(9,9-di-n-octylfluorene)), prolonged
heating of spiro-oligo(fluorene) films resulted in no changes in morphology, emissive color,
and photoluminescence quantum yield. The propensity of spiro-oligo(fluorene)s to thermally
activated crystallization was rationalized with molecular shapes predicted by molecular
mechanics simulations
Spiro-Conjugated Molecular Junctions: Between Jahn–Teller Distortion and Destructive Quantum Interference
No full textThe
quest for molecular structures exhibiting strong quantum interference
effects in the transport setting has long been on the forefront of
chemical research. We establish theoretically that the unusual geometry
of spiro-conjugated systems gives rise to complete destructive interference
in the resonant-transport regime. This results in a current blockade
of the type not present in meta-connected benzene or similar molecular
structures. We further show that these systems can undergo a transport-driven
Jahn–Teller distortion, which can lift the aforementioned destructive-interference
effects. The overall transport characteristics are determined by the
interplay between the two phenomena. Spiro-conjugated systems may
therefore serve as a novel platform for investigations of quantum
interference and vibronic effects in the charge-transport setting.
The potential to control quantum interference in these systems can
also turn them into attractive components in designing functional
molecular circuits
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