Effect of the reaction temperature on the transglycosylation reactions catalyzed by the cyclodextrin glucanotransferase from Bacillus macerans for the synthesis of large-ring cyclodextrins

The synthesis of cyclodextrins with from 6 to more than 50 glucose units by cyclodextrin glucanotransferase (CGTase, EC 2.4.1.19) from Bacillus macerans was investigated. Analysis of the synthesized cyclic α-1,4-glucan products showed that a higher yield of large-ring cyclodextrins were obtained with a reaction temperature of 60 °C compared to 40 °C. The yield of large-ring cyclodextrins obtained at 60 °C represented about 50% of the total glucans employed in the reaction. Analysis of the cyclodextrin-forming cyclization reaction and of the coupling reaction of the CGTase resulting in the degradation of mainly the larger cyclic α-1,4-glucans indicated higher rates of the cyclization reaction at 60 °C compared to 40 °C while the opposite was found for the coupling reaction.     

Effect of ethanol on the synthesis of large-ring cyclodextrins by cyclodextrin glucanotransferases

Cyclodextrin glucanotransferase (EC 2.4.1.19, CGTase) synthesizes cyclodextrins (CD) composed of 6 to more than hundred glucose units from amylose by an intramolecular transglycosylation reaction. The addition of ethanol to the reaction medium resulted in an increase of the yield of large-ring CD obtained with a CGTase from Bacillus sp. BT3-2 and Bacillus macerans. The presence of 15% ethanol in the reaction mixture with the CGTase from Bacillus sp. BT3-2 resulted in a 30% increase of the amounts of CD₁₀–CD₁₃ synthesized after 5 h of reaction. The addition of 20% ethanol increased the yield of CD₁₄–CD₂₁ up to 1000%. The hydrolysis of the large-ring CD by the CGTases was suppressed in the presence of ethanol. The ring-opening coupling cyclization reactions of the CGTase were effected differently by the organic solvent which may contribute to the observed increase of the yield and size of the CD obtained in the synthesis reactions.     

Coupling of butyl vinyl tellurides with metal acetylides catalyzed by nickel complexes

Z-Vinylic tellurides react with metal acetylides under nickel complexes catalysis to give Z-enynes and Z-enediynes in good yields.     

Synthesis of undecaprenyl pyrophosphate-linked glycans as donor substrates for bacterial protein N-glycosylation

Synthesis of undecaprenyl pyrophosphate (Und-PP)-linked glycans is described. Bacterial ([E]₃,[Z]₇)-undecaprenol was synthesized from trans-geranylgeranyl sulfone and isoprenoid building blocks, which was converted to undecaprenyl phosphate (Und-P). It was coupled with glycosyl phosphates to afford Und-PP-linked glycans, including core trisaccharide of Campylobacter jejuni N-glycan. Our synthetic method for Und-PP-linked glycan would provide various substrates as a useful tool for systematic analysis of bacterial protein N-glycosylation.     

Structure and molecular dynamics of solid-state inclusion complexes of cyclodextrin and permethylated cyclodextrin with benzaldehyde studied by high-resolution CP/MAS13C NMR

The structure and molecular dynamics of the benzaldehyde inclusion-complexes with -and-cyclodextrins and permethylated -cyclodextrin in the solid state have been studied by high-resolution cross-polarization/magic angle sample-spinning¹³C NMR spectroscopy. It is shown that the guest benzaldehyde molecule undergoes motion in the host cyclodextrin cavity and the rate of motion depend on the cavity size. In the -cyclodextrin complex, compared to -and permethylated -cyclodextrin complexes, the benzaldehyde motion is severely restricted, but under high-vacuum benzaldehyde is released more easily from the cavity.     

Mechanistic studies on cationic ring-opening polymerisation of cyclodextrin derivatives using various Lewis acids

In order to investigate the potential of cyclodextrins for the preparation of block-like substituted polysaccharides, we submitted mixtures of heptakis[2,3,6-tri-O-methyl]-β-cyclodextrin (Me₂₁-β-CD, 1) and heptakis[2,3,6-tri-O-methyl-d ₃]-β-cyclodextrin ((Me-d ₃)₂₁-β-CD, 2) to cationic ring-opening polymerisation (CROP). Reactions were performed with BF₃·OEt₂, methyl triflate (MeOTf), and Et₃OSbCl₆. Products were compared with respect to their degree of polymerisation (DP) and the average block length (BL). Highest DP was observed with BF₃·OEt₂, while Et₃OSbCl₆ was the most active initiator. Average block length decreased from 14 in the early stage of product formation to about 2 due to competing chain transfer reaction. ¹H NMR spectroscopy, GLC, GLC–MS, ESI-MS and MALDI-TOF-MS were applied for detailed investigations of side reactions. During incubation with BF₃·OEt₂, a stereroisomeric β-CD with one β-glucosidic linkage (Me₂₁-β-CD_6α1β, 3a (Me-d ₃)₂₁-β-CD_{6α 1β}, 3b) is formed as an intermediate, while linear Me₂₁- and (Me-d ₃)₂₁-maltoheptaose (4a/b) was detected in the early stage of the reaction promoted by MeOTf. In the case of Et₃OSbCl₆, both intermediates (3a/b, 4a/b) can be observed during the lag phase of polymerisation, but to a very low degree. End group analysis by GLC reveals that some alkyl exchange occurs at position 3 and 6 in the presence of Et₃OSbCl₆, and that polymerisation is also initiated by protons. Copolymerisation of heptakis[2,3,6-tri-O-benzyl]-β-cyclodextrin (Bn₂₁-β-CD, 5) and Me₂₁-β-CD (1) and subsequent debenzylation yielded a polymer of only 1,4-glcp-Me₃- and 1,4-glcp-residues. Reactivity of Bn₂₁-β-CD was significantly lower than of Me₂₁-β-CD, resulting in higher average block length of 1,4-glcp-Me₃-units.     

以淀粉溶液为催化剂锅三组分法合成四氢苯并[b]吡喃和3,4-二氢吡喃并[c]苯并吡喃衍生物简

Tetrahydrobenzo[b]pyran and 3,4-dihydropyrano[c]chromene derivatives were synthesized via a one-pot three-component condensation of aromatic aldehydes with malononitrile and dimedone or 4-hydroxycoumarin in excellent yields in the presence of starch solution as a highly efficient homogenous catalyst. The use of a nontoxic and biodegradable catalyst, simple work-up procedure, and short reaction time are advantages of this method.     

Isolation of naturally occurring dactylomelane metabolites as Laurencia constituents

Dactylomelol 1, initially isolated from molluscs of the genus Aplysia, was the first example of a monocarbocyclic diterpene skeleton with a C-6-C-11 cyclisation. This paper reports on the identification and structural elucidation of six new diterpenes, compounds 4-9, isolated from specimens of Laurencia sp., together with dactylomelol, all with this particular carbon backbone that we named dactylomelane. This result is the first to confirm a red alga as the biogenetic origin of this class of compounds.     

p-Aminobenzoate ion determination in pharmaceutical formulations by using a potentiometric sensor immobilized in a graphite matrix

The characteristics, performance, and application of an electrode, namely, Pt|Hg|Hg₂(PABzt)₂| graphite, where PABzt stands for p-aminobenzoate ion, are described. This electrode responds to PABzt with sensivity of (58.1±1.0) mV per decade over the range 1.0×10⁻⁴ to 1.0×10⁻¹ mol l⁻¹ at pH 6.5-8.0 and a detection limit of 3.2×10⁻⁵ mol l⁻¹. The electrode shows easy construction, fast response time (within 10-30 s), low-cost, and excellent response stability (lifetime greater than 6 months, in continuous use). The proposed sensor displayed good selectivity for p-aminobenzoate in the presence of several substances, especially, concerning carboxylate and inorganic anions. It was used to determine p-aminobenzoate in pharmaceutical formulations by means of the standard additions method. The results obtained by using this electrode compared very favorably with those given by an HPLC procedure.     

Synthesis of 5-substituted 1H-tetrazoles catalyzed by ytterbium triflate hydrate

Various 5-substituted 1H-tetrazoles were synthesized from aryl nitriles, alkyl nitriles, and vinyl nitriles reacting with sodium azide. The tetrazoles were recovered in high yield under mild conditions when the reaction was catalyzed by ytterbium triflate hydrate in dimethylformamide. Other rare-earth and post-transition metal catalysts were also investigated.     

Click chemistry for facile immobilization of cyclodextrin derivatives onto silica as chiral stationary phases

Click chemistry was applied to immobilize mono-azido-β-cyclodextrin derivatives onto the surface of silica to give novel chiral stationary phases (CSPs). The desired CSPs showed high stability and excellent enantioseparation effects in capillary electrochromatography (CEC).     

Multigram scale synthesis of formyl tetra-O-benzyl-β-d-C-glucopyranoside using benzothiazole as a formyl group equivalent

The addition of 2-lithiobenzothiazole to d-gluconolactone followed by deoxygenation of the resulting ketose affords a mixture of benzothiazolyl α- and β-d-glucopyranoside; treatment of this mixture with sodium methoxide gives the β-anomer from which the title aldehyde is obtained in a pure form by transformation of the benzothiazole ring into the formyl group.     

Sonogashira reactions catalyzed by a new and efficient copper(I) catalyst incorporating N-benzyl DABCO chloride

A new and effective catalytic system using [N-benzyl DABCO]⁺[Cu₄Cl₅]⁻ was developed for the palladium-free Sonogashira cross-coupling reactions of phenylacetylene with a variety of aryl halides. In this homogeneous catalytic system, 1-benzyl-4-aza-1-azoniabicyclo[2.2.2]octane chloride, a quaternary ammonium salt containing a coordinating center, plays an important role and increases the efficiency of Cu(I) species during the reaction. A number of internal alkynes were produced in moderate to excellent yields, in short reaction times in DMF at 135 °C.     

Synthesis of meso-tetraarylporphyrins using SeO2 as oxidant

The oxidative step of the two-step, one-flask synthesis of meso-tetraarylporphyrins is herein conducted with heterogeneous oxidant SeO₂ instead of the usual quinones DDQ or p-chloranil. Evaluation of BF₃O(Et)₂ or I₂ amount for the condensation of the first step combined with the excess of SeO₂ defined porphyrin synthesis conditions employing benzaldehydes and pyrrole (or 5-phenyldipyrromethane) as starting materials. The simplicity of the workup, allied with reaction mild conditions, makes this method a good option for the synthesis of this kind of compound.     

Selective cyclization of alkynols and alkynylamines catalyzed by potassium tert-butoxide

Potassium tert-butoxide (t-BuOK) was found to be an effective catalyst for the cyclization of aromatic alkynols and alkynylamines. In the presence of 10 mol % t-BuOK, a range of alkynols were converted to the corresponding exo-cyclic enol ethers as pure Z-stereoisomers with 100% selectivity and moderate to excellent yields. Moreover, the cyclization of alkynylamines was also achieved to afford indoles and isoindolin-1-ones in good yields.     

Synthesis of (+)-anatoxin-a using enyne metathesis

Synthesis of N-tosylanatoxin-a was achieved by metathesis of enyne in cis-substituents on a pyrrolidine derivative. Metathesis reactions of enyne having terminal alkyne using various ruthenium-carbene complexes did not give a good results. However, when the terminal alkyne was protected with a TMS group, the reaction proceeded smoothly using a second-generation ruthenium-carbene complex to give the desired cyclized compound in high yield. Oxymercuration followed by Dess-Martin oxidation afforded N-tosylanatoxin-a.     

Synthesis of ginsenoside Rh2 and chikusetsusaponin-LT8 via gold(I)-catalyzed glycosylation with a glycosyl ortho-alkynylbenzoate as donor

Glycosylation of the acid labile protopanaxadiol derivatives was succeeded with a glycosyl ortho-hexynylbenzoate as donor under the catalysis of PPh₃AuNTf₂, leading to the subsequent elaboration of ginsenoside Rh2 and chikusetsusaponin-LT8 in a concise manner.     

Synthesis of indoles with a polyfluorinated benzene ring

A two-step sequence consisting of a Sonogashira coupling of polyfluorinated 2-iodoanilines with terminal alkynes, followed by a KOH promoted cyclization of the 2-alkynylanilines thus formed, has been developed as a one-pot synthesis of 2-R-indoles (R=n-Bu, Ph, CH₂OTHP→CH₂OH, C(CH₃)₂OH→H) containing a polyfluorinated benzene moiety.     

Cyanosilylation of aldehydes catalyzed by N-heterocyclic carbenes

N-Heterocyclic carbenes produced in situ from salts of imidazolium, benzimidazolium, pyrido[1,2-c]imidazolium, imidazolinium, thiazolium, and triazolium catalyze the addition of trimethylsilylcyanide to aldehydes to yield cyanohydrin trimethylsilyl ethers. The use of C₂-symmetric imidazolidenyl carbene derived from (R,R)-1,3-bis[(1-naphthyl)ethyl]imidazolium chloride led to enantioselective cyanosilylation.     

Efficient synthesis of carbonyl compounds: oxidation of azides and alcohols catalyzed by vanadium pentoxide in water using tert-butylhydroperoxide

Catalytic amount of vanadium reagent with tert-butylhydroperoxide as the oxidant was found to be an excellent oxidizing agent in aqueous medium. Vanadium pentoxide with aq tert-butylhydroperoxide readily oxidizes primary benzylic azides to the corresponding acids and secondary benzylic azides to the corresponding ketones in excellent yields. Further, vanadium pentoxide and aq tert-butylhydroperoxide combination turned out to be an effective catalyst for the oxidation of alcohols. Using vanadium pentoxide and aq tert-butylhydroperoxide primary alcohols were oxidized to the corresponding acids, whereas secondary alcohols underwent a smooth transformation to furnish corresponding ketones in excellent yields. All the oxidations are performed in water.