An efficient regio-specific synthetic route to multiply substituted acyl-sulphated β-cyclodextrins

Enrofloxacin Pharmaceutical Formulations through the Polymer-Free Electrospinning of β-Cyclodextrin-oligolactide Derivatives

Enrofloxacin (ENR), a member of the fluoroquinolone class of antibiotics, is widely used in veterinary medicine to treat bacterial infections. Like many antibiotics, ENR has limited water solubility and low bioavailability. To address these challenges, drug formulations using solid dispersions, nanosuspensions, surfactants, cocrystal/salt formation, and inclusion complexes with cyclodextrins may be employed. The approach described herein proposes the development of ENR formulations by co-electrospinning ENR with custom-prepared cyclodextrin-oligolactide (CDLA) derivatives. This method benefits from the high solubility of these derivatives, enabling polymer-free electrospinning. The electrospinning parameters were optimized to incorporate significant amounts of ENR into the CDLA nanofibrous webs, reaching up to 15.6% by weight. The obtained formulations were characterized by FTIR and NMR spectroscopy methods and evaluated for their antibacterial activity against Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa. This study indicates that the presence of CDLA derivative does not inhibit the antibacterial activity of ENR, recommending these formulations for further development.

Mass Spectrometry of Esterified Cyclodextrins

Cyclodextrins are cyclic oligosaccharides that have received special attention due to their cavity-based structural architecture that imbues them with outstanding properties, primarily related to their capacity to host various guest molecules, from low-molecular-mass compounds to polymers. Cyclodextrin derivatization has been always accompanied by the development of characterization methods, able to unfold complicated structures with increasing precision. One of the important leaps forward is represented by mass spectrometry techniques with soft ionization, mainly matrix-assisted laser desorption/ionization (MALDI) and electrospray ionization (ESI). In this context, esterified cyclodextrins (ECDs) benefited also from the formidable input of structural knowledge, thus allowing the understanding of the structural impact of reaction parameters on the obtained products, especially for the ring-opening oligomerization of cyclic esters. The current review envisages the common mass spectrometry approaches such as direct MALDI MS or ESI MS analysis, hyphenated liquid chromatography-mass spectrometry, and tandem mass spectrometry, employed for unraveling the structural features and particular processes associated with ECDs. Thus, the accurate description of complex architectures, advances in the gas phase fragmentation processes, assessment of secondary reactions, and reaction kinetics are discussed in addition to typical molecular mass measurements.

A comprehensive review on bio-mimicked multimolecular frameworks and supramolecules as scaffolds for enzyme immobilization

Immobilization depicts a propitious route to optimize the catalytic performances, efficient recovery, minimizing autocatalysis, and also augment the stabilities of enzymes, particularly in unnatural environments. In this opinion, supramolecules and multimolecular frameworks have captivated immense attention to achieve profound controllable interactions between enzyme molecules and well-defined natural or synthetic architectures to yield protein bioconjugates with high accessibility for substrate binding and enhanced enantioselectivities. This scholastic review emphasizes the possibilities of associating multimolecular complexes with biological entities via several types of interactions, namely covalent interactions, host-guest complexation, π - π ${\rm{\pi }}-{\rm{\pi }}$ interactions, intra/inter hydrogen bondings, electrostatic interactions, and so forth offers remarkable applications for the modulations of enzymes. The potential synergies between artificial supramolecular structures and biological systems are the primary concern of this pedagogical review. The majority of the research primarily focused on the dynamic biomolecule-responsive supramolecular assemblages and multimolecular architectures as ideal platforms for the recognition and modulation of proteins and cells. Embracing sustainable green demeanors of enzyme immobilizations in a quest to reinforce site-selectivity, catalytic efficiency, and structural integrality of enzymes are the contemporary requirements of the biotechnological sectors that instigate the development of novel biocatalytic systems.

Amphiphilic cyclodextrin nanoparticles

Cyclodextrins are cyclic oligosaccharides obtained by enzymatic digestion of starch. The α-, β- and γ- cyclodextrins contain respectively 6, 7 and 8 glucopyranose units, with primary and secondary hydroxyl groups located on the narrow and wider rims of a truncated cone shape structure. Such structure is that of a hydrophobic inner cavity with a hydrophilic outer surface allowing to interact with a wide range of molecules like ions, protein and oligonucleotides to form inclusion complexes. Many cyclodextrin applications in the pharmaceutical area have been widely described in the literature due to their low toxicity and low immunogenicity. The most important is to increase the solubility of hydrophobic drugs in water. Chemically modified cyclodextrin derivatives have been synthesized to enhance their properties and more specifically their pharmacological activity. Among these, amphiphilic derivatives were designed to build organized molecular structures, through selfassembling systems or by incorporation in lipid membranes, expected to improve the vectorization in the organism of the drug-containing cyclodextrin cavities. These derivatives can form a variety of supramolecular structures such as micelles, vesicles and nanoparticles. The purpose of this review is to summarize applications of amphiphilic cyclodextrins in different areas of drug delivery, particularly in protein and peptide drug delivery and gene delivery. The article highlights important amphiphilic cyclodextrin applications in the design of novel delivery systems like nanoparticles.

Cyclodextrin-based supramolecular systems for drug delivery: recent progress and future perspective

The excellent biocompatibility and unique inclusion capability as well as powerful functionalization capacity of cyclodextrins and their derivatives make them especially attractive for engineering novel functional materials for biomedical applications. There has been increasing interest recently to fabricate supramolecular systems for drug and gene delivery based on cyclodextrin materials. This review focuses on state of the art and recent advances in the construction of cyclodextrin-based assemblies and their applications for controlled drug delivery. First, we introduce cyclodextrin materials utilized for self-assembly. The fabrication technologies of supramolecular systems including nanoplatforms and hydrogels as well as their applications in nanomedicine and pharmaceutical sciences are then highlighted. At the end, the future directions of this field are discussed.

Molecular buckets: cyclodextrins for oral cancer therapy

The oral route is preferred by patients for drug administration due to its convenience, resulting in improved compliance. Unfortunately, for a number of drugs (e.g., anticancer drugs), this route of administration remains a challenge. Oral chemotherapy may be an attractive option and especially appropriate for chronic treatment of cancer. However, this route of administration is particularly complicated for the administration of anticancer drugs ascribed to Class IV of the Biopharmaceutical Classification System. This group of compounds is characterized by low aqueous solubility and low intestinal permeability. This review focuses on the use of cyclodextrins alone or in combination with bioadhesive nanoparticles for oral delivery of drugs. The state-of-the-art technology and challenges in this area is also discussed.

[Amphiphilic cyclodextrins and their applications. Preparation of nanoparticles based on amphiphilic cyclodextrins for biomedical applications]

Solubilization of hydrophobic drugs at the molecular level as inclusion complexes inside cyclodextrins (CDs) offers a good alternative for improving their stability, solubility and bioavailability, and for preventing against their possible toxicity or controlling secondary effects. Therefore CDs are widely used as solubilizing excipients. However since dissociation takes place too readily upon dilution, inclusion complexes inside simple water-soluble CD appears ineffective for drug delivery applications. Chemical modifications of CDs allow them to self-organize as larger assemblies useful for resolving this lability issue. Depending on the position, the number and the nature of these groups, amphiphilic CDs can form assemblies such as vesicles, solid-lipid nanoparticles, nanospheres, liquid crystals, or micellar systems. This review deals with the synthesis of amphiphilic cyclodextrins leading to supramolecular assemblies and the physical properties of these assemblies. From the first sulfonated amphiphilic cyclodextrins isolated in our laboratory in 2003, to the latest ones being regioselectively functionalized by two or four fluoroalkyl chains, through the persubstituted fluorinated cyclodextrines, all these amphiphilic cyclodextrins have shown good abilities for encapsulation. Complexation of bioactive molecules (acyclovir) by these modified alpha-cyclodextrin derivatives, the encapsulation efficiency and release profile were measured as an assessment of the properties of such nanoparticles regarding drug delivery applications.

Novel nanoparticles made from amphiphilic perfluoroalkyl alpha-cyclodextrin derivatives: preparation, characterization and application to the transport of acyclovir

The preparation of aqueous suspensions of nanoparticles of the fluorinated amphiphilic alpha-cyclodextrins hexakis[6-deoxy-6-(3-perfluoroalkylpropanethio)-2,3-di-O-methyl]-alpha-cyclodextrin and their hydrocarbon analogues was studied. The complexation of acyclovir by modified alpha-cyclodextrin, the encapsulation efficiency and release profile were measured as an assessment of the properties of such nanoparticles regarding drug delivery applications. Stable aqueous suspensions of nanoparticles were prepared using nanoprecipitation method without using surface-active agent. The organic solvent (ethanol) and cyclodextrin concentration (0.4 mM) were carefully selected. The nanoparticles prepared from these new amphiphilic alpha-cyclodextrin derivatives according to optimized conditions have an average diameter of 100 nm for fluorinated derivatives and 150 nm for hydrocarbon analogues. Suspensions were stable over at least 9 months. Acyclovir forms inclusion complexes of 1:1 stoichiometry and high stability constants (from 700 mol L(-1) to 4000 mol L(-1) in ethanol) as assessed from UV/vis spectroscopy and Electrospray Ionization Mass Spectroscopy. Satisfactory loading of acyclovir inside the nanoparticles was achieved according to the "highly loaded" preparation method (encapsulation efficiency approximately 40%). Nanoparticles based on the fluorinated compounds delayed the drug release up to 3 h with little initial burst release. Fluorinated amphiphilic alpha-cyclodextrins self-assemble in the form of nanospheres that encapsulate acyclovir and allow sustained release, showing their potential for applications to drug delivery.

Synthesis and characterization of an amphiphilic cyclodextrin, a micelle with two recognition sites

A cyclodextrin derivative (Mod-CD) was synthesized through the monoesterification of beta-cyclodextrin (beta-CD) with 3-((E)-dec-2-enyl)-dihydrofuran-2,5-dione. The compound is an interesting surfactant that can form large aggregates not only through the interaction of the hydrophobic tails as in common amphiphilic compounds but also through the inclusion of the alkenyl chain into the cavity of another Mod-CD molecule. The self-inclusion of the chain in the cavity of cyclodextrin as well as the intermolecular inclusion was demonstrated by 1H NMR measurements that were able to detect methyl groups in three different environments. Besides, in the aggregates of Mod-CD, the cavity is available to interact with external guests such as phenolphthalein, 1-amino adamantane, and Prodan. Phenolphthalein has the same binding constant with Mod-CD and beta-CD, but the equilibrium constant for the interaction with Prodan is about 2 times larger for Mod-CD than for beta-CD. The latter result is attributed to the fact that this probe interacts with the micelle in two binding sites: the cavity of the cyclodextrin and the apolar heart of the micelle as evidenced by the spectrofluorimetric behavior of Prodan in solutions containing different concentrations of Mod-CD.

Regioselective synthesis of cyclodextrin mono-substituted conjugates of non-steroidal anti-inflammatory drugs at C-2 secondary hydroxyl by protease in non-aqueous media

Three beta-cyclodextrin (beta-CD) conjugates of non-steroidal anti-inflammatory drugs were synthesized by enzymatic methods. Transesterification of beta-CD with vinyl ester of indomethacin, ketoprofen and etodolac was performed by the catalysis of alkaline protease from Bacillus subtilis in anhydrous DMF for 3 days. The drug molecules were selectively conjugated onto one of the secondary hydroxyl groups of beta-CD through ester-linkage to improve their poor water solubility and absorption characteristics. The products were characterized by ESI-MS, (1)H NMR and (13)C NMR. The structures of products with monoacylation occurring at the C-2 secondary hydroxyl groups of beta-CD were confirmed.

Evidence of a self-inclusion phenomenon for a new class of mono-substituted alkylammonium-β-cyclodextrins

A new class of mono-substituted N-alkyl-N,N-dimethylammonium-beta-cyclodextrins has been synthesized in a three step procedure from the native beta-cyclodextrin. The structural analysis of these compounds undertaken by combined use of 1D and 2D NMR spectra indicate that the two methyl groups bound on the nitrogen are magnetically inequivalent due to a self-inclusion phenomenon of the alkyl chain inside the CD cavity. A variable-temperature 1H NMR study showed that these mono-substituted CD derivatives formed temperature-independent intramolecular complexes with their own alkylammonium substituent. The strength of the interaction between the alkyl moiety and the cyclodextrin cavity has been evaluated by a competitive method using an adamantane derivative. Finally, surface tension measurements demonstrated the surface active character of these compounds and confirmed their self-inclusion ability.

Synthesis and characterisation of sulfated amphiphilic alpha-, beta- and gamma-cyclodextrins: application to the complexation of acyclovir

The synthesis of sulfated amphiphilic alpha-, beta- and gamma-cyclodextrins was achieved according to the standard protection-deprotection procedure. The formation of inclusion complexes between the amphiphilic alpha-, beta- and gamma-cyclodextrins and an antiviral molecule, acyclovir (ACV) was investigated by UV-visible spectroscopy (UV-Vis) and electrospray ionisation mass spectrometry (ESIMS). UV-Vis spectroscopy allowed determination of the stoichiometry and stability constants of complexes, whereas ESIMS, a soft ionisation technique, allowed the detection of the inclusion complexes. The results showed that the non-sulfated amphiphilic cyclodextrins exhibit a 1:2 stoichiometry with acyclovir, while sulfated amphiphilic cyclodextrins, except gamma-cyclodextrin, exhibit a 1:1 stoichiometry indicating the loss of one interaction site. Non-covalent interactions between acyclovir and non-sulfated amphiphilic cyclodextrins appear to take place both in the cavity of the cyclodextrin and inside the hydrophobic zone generated by alkanoyl chains. In contrast, in the case of sulfated amphiphilic cyclodextrins, the interactions appear to involve only the hydrophobic region of the alkanoyl chains.

Regioselective monoacylation of cyclomaltoheptaose at the C-2 secondary hydroxyl groups by the alkaline protease from Bacillus subtilis in nonaqueous media

Transesterification of cyclomaltoheptaose (beta-CD) with divinyl butanedioate, divinyl hexanedioate, and divinyl decanedioate, catalyzed by the alkaline protease from Bacillus subtilis in anhydrous DMF for 5 days, furnished the corresponding vinyl-beta-CD derivatives. The products were characterized by ESI-MS, (1)H NMR, (13)C NMR, IR, and DSC. The results indicated the products to be monosubstituted esters, with monoacylation occurring at the C-2 secondary hydroxyl groups of beta-CD. The regioselectivity of the monoacylation as catalyzed by alkaline protease was not affected by the chain length of the acyl donor.

A practical synthesis of amphiphilic cyclodextrins fully substituted with sugar residues on the primary face

New amphiphilic cyclodextrins fully substituted with sugar residues on the primary face have been synthesised and enzymatically modified.

Scanning electron microscopy and atomic force microscopy imaging of solid lipid nanoparticles derived from amphiphilic cyclodextrins

Scanning electron microscopy (SEM) and atomic force microscopy (AFM) have been applied to the imagery of solid lipid nanoparticles (SLNs) formulated from an amphiphilic cyclodextrin, 2,3-di-o-alkanoyl-beta-cyclodextrin, beta-CD21C6. Comparison of the results shows that the vacuum drying technique used in sample preparation for SEM causes shrinkage in the size of the SLNs, whereas the deposition method used for AFM causes the SLNs to form small clusters. The hydrodynamic diameter determined from photon correlation spectroscopy (PCS) is 359+/-15 nm and the zeta potential is -25 mV.

Interfacial interactions between amphiphilic cyclodextrins and physiologically relevant cations

The compression isotherms of a series of amphiphilic cyclodextrins, formed (a) by acylation at the secondary hydroxyl face and (b) by acylation accompanied by varying degrees of sulfatation (DS) at the primary hydroxyl face (DS=0, 4, and 7), have been studied on subphases of pure water and of water containing NaCl, KCl, MgCl(2), and CaCl(2) at inter- and extracellular concentrations. The formation of solid lipid nanoparticles (SLNs) by two of the molecules has been observed, while these do not aggregate at concentrations of monovalent salts up to 150 mM for the sulfated derivative. In the presence of divalent salts one of these with a DS=0 for sulfatation degree flocculates at divalent salt concentrations below 0.1 mM while the other with a DS=4 flocculates at Mg(2+) concentration above 5 mM and a Ca(2+) concentration above 3 mM. AFM noncontact mode imaging has been carried out, in air, for the SLNs deposited on mica.