Cryptophane-xenon complexes for 129Xe MRI applications

The use of magnetic resonance imaging (MRI) and spectroscopy (MRS) in the clinical setting enables the acquisition of valuable anatomical information in a rapid, non-invasive fashion. However, MRI applications for identifying disease-related biomarkers are limited due to low sensitivity at clinical magnetic field strengths. The development of hyperpolarized (hp) ¹²⁹Xe MRI/MRS techniques as complements to traditional ¹H-based imaging has been a burgeoning area of research over the past two decades. Pioneering experiments have shown that hp ¹²⁹Xe can be encapsulated within host molecules to generate ultrasensitive biosensors. In particular, xenon has high affinity for cryptophanes, which are small organic cages that can be functionalized with affinity tags, fluorophores, solubilizing groups, and other moieties to identify biomedically relevant analytes. Cryptophane sensors designed for proteins, metal ions, nucleic acids, pH, and temperature have achieved nanomolar-to-femtomolar limits of detection via a combination of ¹²⁹Xe hyperpolarization and chemical exchange saturation transfer (CEST) techniques. This review aims to summarize the development of cryptophane biosensors for ¹²⁹Xe MRI applications, while highlighting innovative biosensor designs and the consequent enhancements in detection sensitivity, which will be invaluable in expanding the scope of ¹²⁹Xe MRI.

This review aims to summarize the development of cryptophane biosensors for ¹²⁹Xe MRI applications, while highlighting innovative biosensor designs and the consequent enhancements in detection sensitivity, which will be invaluable in expanding the scope of ¹²⁹Xe MRI.

Regioselective chemoenzymatic syntheses of ferulate conjugates as chromogenic substrates for feruloyl esterases

Generally, carbohydrate-active enzymes are studied using chromogenic substrates that provide quick and easy color-based detection of enzyme-mediated hydrolysis. For feruloyl esterases, commercially available chromogenic ferulate derivatives are both costly and limited in terms of their experimental application. In this study, we describe solutions for these two issues, using a chemoenzymatic approach to synthesize different ferulate compounds. The overall synthetic routes towards commercially available 5-bromo-4-chloro-3-indolyl and 4-nitrophenyl 5-O-feruloyl-α-ʟ-arabinofuranosides were significantly shortened (from 7 or 8 to 4–6 steps), and the transesterification yields were enhanced (from 46 to 73% and from 47 to 86%, respectively). This was achieved using enzymatic (immobilized Lipozyme^® TL IM from Thermomyces lanuginosus) transesterification of unprotected vinyl ferulate to the primary hydroxy group of α‐ʟ‐arabinofuranosides. Moreover, a novel feruloylated 4-nitrocatechol-1-yl-substituted butanetriol analog, containing a cleavable hydroxylated linker, was also synthesized in 32% overall yield in 3 steps (convergent synthesis). The latter route combined the regioselective functionalization of 4-nitrocatechol and enzymatic transferuloylation. The use of this strategy to characterize type A feruloyl esterase from Aspergillus niger reveals the advantages of this substrate for the characterizations of feruloyl esterases.

Non-ionic PEG-oligoglycerol dendron conjugated nano-carriers for dermal drug delivery

A new class of non-ionic amphiphiles have been synthesised using a combination of polyethylene glycol (PEG) and oligoglycerol dendrons as hydrophilic units and an alkoxy aryl moiety as hydrophobic unit. The resulting amphiphiles were found to aggregate in aqueous medium. Their aggregation behaviour was studied using dynamic light scattering (DLS), fluorescence spectroscopy, and cryogenic electron microscopy (cryo-TEM). The inner hydrophobic core of these aggregates in aqueous medium is capable of encapsulating lipophilic guest molecules. The encapsulation behaviour was studied using Nile red as a hydrophobic dye as well as Curcumin and Dexamethasone as hydrophobic drug candidates. Furthermore, for biological evaluation, cytotoxicity and cellular uptake was studied using different cancer cell lines. The biomedical application of synthesised amphiphiles was further investigated for dermal drug delivery on excised human skin using Nile red encapsulated in the nanocarrier. The release profile of drug/dye encapsulated amphiphiles was studied under physiochemical conditions in the presence of immobilized lipase Novozym 435.

Chemoenzymatic Synthesis, Nanotization, and Anti-Aspergillus Activity of Optically Enriched Fluconazole Analogues

Despite recent advances in diagnostic and therapeutic methods in antifungal research, aspergillosis still remains a leading cause of morbidity and mortality. One strategy to address this problem is to enhance the activity spectrum of known antifungals, and we now report the first successful application of Candida antarctica lipase (CAL) for the preparation of optically enriched fluconazole analogues. Anti-Aspergillus activity was observed for an optically enriched derivative, (-)-S-2-(2',4'-difluorophenyl)-1-hexyl-amino-3-(1‴,2‴,4‴)triazol-1‴-yl-propan-2-ol, which exhibits MIC values of 15.6 μg/ml and 7.8 μg/disc in broth microdilution and disc diffusion assays, respectively. This compound is tolerated by mammalian erythrocytes and cell lines (A549 and U87) at concentrations of up to 1,000 μg/ml. When incorporated into dextran nanoparticles, the novel, optically enriched fluconazole analogue exhibited improved antifungal activity against Aspergillus fumigatus (MIC, 1.63 μg/ml). These results not only demonstrate the ability of biocatalytic approaches to yield novel, optically enriched fluconazole derivatives but also suggest that enantiomerically pure fluconazole derivatives, and their nanotized counterparts, exhibiting anti-Aspergillus activity may have reduced toxicity.

Biocatalytic Synthesis of Novel Partial Esters of a Bioactive Dihydroxy 4-Methylcoumarin by Rhizopus oryzae Lipase (ROL)

Highly regioselective acylation has been observed in 7,8-dihydroxy-4-methylcoumarin (DHMC) by the lipase from Rhizopus oryzae suspended in tetrahydrofuran (THF) at 45 °C using six different acid anhydrides as acylating agents. The acylation occurred regioselectively at one of the two hydroxy groups of the coumarin moiety resulting in the formation of 8-acyloxy-7-hydroxy-4-methylcoumarins, which are important bioactive molecules for studying biotansformations in animals, and are otherwise very difficult to obtain by only chemical steps. Six monoacylated, monohydroxy 4-methylcoumarins have been biocatalytically synthesised and identified on the basis of their spectral data and X-ray crystal analysis.

Synthesis of macromolecular systems via lipase catalyzed biocatalytic reactions: applications and future perspectives

This review highlights the application of lipases in the synthesis of pharmaceutically important small molecules and polymers for diverse applications.

Fabrication of honeycomb films from highly functional dendritic structures: electrostatic force driven immobilization of biomolecules

Herein we report the preparation of honeycomb porous films for selective immobilization of biomolecules via the breath figure technique, a water-assisted micropatterning method.

Novozym 435-catalyzed syntheses of polyesters and polyamides of medicinal and industrial relevance

The adverse impact of chemical and biochemical waste on the environment and human health poses a serious challenge in today's World. The best way to address these challenges is to reduce the waste by developing more efficient processes and technologies, based on the principles of "green chemistry". Some of these synthetic approaches involving the chemoenzymatic synthetic methodologies are discussed herein. These lead to the formation of unique nanomaterials with diverse applications, such as drugs/gene delivery systems, flame retardant materials, conducting polymers, controlled release systems, diagnostic agents, and polymeric electrolytes for nanocrystalline solar cells.

Dendritic polyglycerol cyclodextrin amphiphiles and their self-assembled architectures to transport hydrophobic guest molecules

Microwave-assisted synthesis of cyclodextrin–polyglycerol based amphiphilic dendrimers and their self-assembly to form well-defined nanostructures in aqueous solutions are reported here.

Non-ionic dendronized multiamphiphilic polymers as nanocarriers for biomedical applications

A new class of non-ionic dendronized multiamphiphilic polymers is prepared from a biodegradable (AB)n-type diblock polymer synthesized from 2-azido-1,3-propanediol (azido glycerol) and polyethylene glycol (PEG)-600 diethylester using Novozym-435 (Candida antarctica lipase) as a biocatalyst, following a well-established biocatalytic route. These polymers are functionalized with dendritic polyglycerols (G1 and G2) and octadecyl chains in different functionalization levels via click chemistry to generate dendronized multiamphiphilic polymers. Surface tension measurements and dynamic light scattering studies reveal that all of the multiamphiphilic polymers spontaneously self-assemble in aqueous solution. Cryogenic transmission electron microscopy further proves the formation of multiamphiphiles towards monodisperse spherical micelles of about 7-9 nm in diameter. The evidence from UV-vis and fluorescence spectroscopy suggests the effective solubilization of hydrophobic guests like pyrene and 1-anilinonaphthalene-8-sulfonic acid within the hydrophobic core of the micelles. These results demonstrate the potential of these dendronized multiamphiphilic polymers for the development of prospective drug delivery systems for the solubilization of poorly water soluble drugs.

Biocatalytic route to sugar-PEG-based polymers for drug delivery applications

Sugar-PEG-based polymers were synthesized by enzymatic copolymerization of 4-C-hydroxymethyl-1,2-O-isopropylidene-β-L-threo-pentofuranose/4-C-hydroxymethyl-1,2-O-benzylidene-β-L-threo-pentofuranose/4-C-hydroxymethyl-1,2-O-isopropylidene-3-O-pentyl-β-L-threo-pentofuranose with PEG-600 dimethyl ester using Novozyme-435 (Candida antarctica lipase immobilized on polyacrylate). Carbohydrate monomers were obtained by the multistep synthesis starting from diacetone-D-glucose and PEG-600 dimethyl ester, which was in turn obtained by the esterification of the commercially available PEG-600 diacid. Aggregation studies on the copolymers revealed that in aqueous solution those polymers bearing the hydrophobic pentyl/benzylidene moiety spontaneously self-assembled into supramolecular aggregates. The critical aggregation concentration (CAC) of polymers was determined by surface tension measurements, and the precise size of the aggregates was obtained by dynamic light scattering. The polymeric aggregates were further explored for their drug encapsulation properties in buffered aqueous solution of pH 7.4 (37 °C) using nile red as a hydrophobic model compound by means of UV/vis and fluorescence spectroscopy. There was no significant encapsulation in polymer synthesized from 4-C-hydroxymethyl-1,2-O-isopropylidene-β-L-threo-pentofuranose because this sugar monomer does not contain a big hydrophobic moiety as the pentyl or the benzylidene moiety. Nile red release study was performed at pH 5.0 and 7.4 using fluorescence spectroscopy. The release of nile red from the polymer bearing benzylidene moiety and pentyl moiety was observed with a half life of 3.4 and 2.0 h, respectively at pH 5.0, whereas no release was found at pH 7.4.