Andrew N. Boa

Protein free microcapsules obtained from plant spores as a model for drug delivery: ibuprofen encapsulation, release and taste masking

Sporopollenin exine capsules (SEC) extracted from Lycopodium clavatum spores were shown to encapsulate ibuprofen as a drug model, with 97 ± 1% efficiency as measured by recovery of the loaded drug and absence of the drug on the SEC surface by scanning electron microscopy (SEM). The encapsulated ibuprofen was shown to be unchanged from its bulk crystalline form by solid state NMR, FTIR and XRD. Essential for drug delivery applications, SEC were shown to be non-toxic to human endothelial cells and free of allergenic protein epitopes by MALDI-TOF-MS and ESI-QqToF-MS. Potential application for targeted release into the intestinal region of the gastrointestinal tract (GIT) was demonstrated by 88 ± 1% of the drug being retained in simulated gastric fluid (SGF) after 45 minutes and 85 ± 2% being released after 5 min in buffer (PBS; pH 7.4). The SEC were shown to provide significant taste masking of encapsulated ibuprofen in a double blind trial with 10 human volunteers.

A simple preparation of iodoarenes, iodoalkenes and iodoalkynes by reaction of organolithiums with 2,2,2-trifluoro-1-iodoethane

Abstract Organolithium anions, generated either by deprotonation or lithium-bromine exchange, when quenched with 2,2,2-trifluoro-1-iodoethane produce cleanly the synthetically useful iodoarenes, iodoalkenes and iodoalkynes.

Sporopollenin, The Least Known Yet Toughest Natural Biopolymer

Sporopollenin is highly cross-linked polymer composed of carbon, hydrogen and oxygen that is extraordinarily stable and has been found chemically intact in sedimentary rocks some 500 million year old. It is the outer shell (exine) of plant spores and pollen and when extracted it is in the form of an empty exine or microcapsule. The exines resemble the spores and pollen from which they are extracted, in size and morphology. Also, from any one plant such characteristics are incredible uniform. The exines can be used is microcapsules or simply as micron-sized particles due to the variety of functional groups on their surfaces. The loading of the exine microcapsules into their cavities is via multi-directional nano-diameter sized channels. The exines can be filled with a variety of polar and non-polar materials. Such as enzymes can be encapsulated within the shells and still remain active. In vivo studies in humans have shown that an encapsulated active substance can have a substantially increased bioavailability than if it is taken alone. The sporopollenin exine surface possesses phenolic, alkane, alkene, ketone, lactone and carboxylic acid groups. Therefore it can be derivatised in a number of ways, which has given rise to its having been used for, such as, solid supported for peptide synthesis, catalysis and ion-exchange chromatography. Also, the presence of the phenolic groups on sporopollenin endows it with antioxidant activity.

Sequestration of edible oil from emulsions using new single and double layered microcapsules from plant spores

Microcapsules were obtained conveniently from Lycopodium clavatum spores possessing either a single layered shell of sporopollenin (exine) or double layered shell of sporopollenin and cellulose with an inner layer (intine). These microcapsules were further modified by converting their surface hydroxyl groups (alcohols, phenols carboxylic acids) into salts (Na+ and K+), acetates and methyl ethers accordingly. All of these new types of microcapsules were found to sequester efficiently edible oils from oil-in-water emulsions with the acetylated forms being the most efficient to sequester oils in near quantitative fashion. The latter could be recycled without losing efficiency to recover oil. Oils could also be released from the microcapsules in a stepwise manner by repeated rubbing.

Sporopollenin capsules at fluid interfaces: particle-stabilised emulsions and liquid marbles

Hollow particles of sporopollenin from spores of the plant Lycopodium clavatum have been prepared. These particles possess ionisable groups on their surface such that they become increasingly negatively charged with an increase in pH. The particles adsorb to both air–water and oil–water interfaces, stabilising liquid marbles and emulsions respectively. Water marbles can be formed at all pH values between 2 and 10 and for salt concentrations up to 1 M NaCl. Their stability to evaporation is greater than the equivalent bare water drop. Deformation and buckling of the marbles occur as water is lost due to the solid-like nature of the liquid surface. Transitional phase inversion of emulsions occurs from water-in-oil to oil-in-water with increasing pH, with that corresponding to inversion depending on the oil type. Emulsion drops of millimetre size are stable to coalescence due to a close packed layer of particles at their surfaces.

TRPA1 is activated by direct addition of cysteine residues to the N-hydroxysuccinyl esters of acrylic and cinnamic acids.

The nociceptor TRPA1 is thought to be activated through covalent modification of specific cysteine residues on the N terminal of the channel. The precise mechanism of covalent modification with unsaturated carbonyl-containing compounds is unclear, therefore by examining a range of compounds which can undergo both conjugate and/or direct addition reactions we sought to further elucidate the mechanism(s) whereby TRPA1 can be activated by covalent modification. Calcium signalling was used to determine the mechanism of activation of TRPA1 expressed in HEK293 cells with a series of related compounds which were capable of either direct and/or conjugate addition processes. These results were confirmed using physiological recordings with isolated vagus nerve preparations. We found negligible channel activation with chemicals which could only react with cysteine residues via conjugate addition such as acrylamide, acrylic acid, and cinnamic acid. Compounds able to react via either conjugate or direct addition, such as acrolein, methyl vinyl ketone, mesityl oxide, acrylic acid NHS ester, cinnamaldehyde and cinnamic acid NHS ester, activated TRPA1 in a concentration dependent manner as did compounds only capable of direct addition, namely propionic acid NHS ester and hydrocinnamic acid NHS ester. These compounds failed to activate TRPV1 expressed in HEK293 cells or mock transfected HEK293 cells. For molecules capable of direct or conjugate additions, the results suggest for the first time that TRPA1 may be activated preferentially by direct addition of the thiol group of TRPA1 cysteines to the agonist carbonyl carbon of α,β-unsaturated carbonyl-containing compounds.

Access to a primary aminosporopollenin solid support from plant spores

Sporopollenin, which is a naturally occurring and highly resilient organic polymer constituting the external shell of spores and pollen grains, has been converted into a primary amine form with a loading of 0.58 ±0.04 mmol.g−1 by reductive amination with ammonia and lithium aluminium hydride successively. The presence of the amine and precursor amide groups were established by combustion elemental analysis, ICP-OES, FTIR, solid-state NMR and reactivity of the primary amine group to salt formation and nucleophilic addition and substitution with phenyl isothiocyanate and benzene sulfonyl chloride, respectively. This relatively simple conversion has served to provide further information regarding the presence and reactivity of carboxylic acid functions on this relatively uncharted polymer and offers aminosporopollenin as a new material for potential solid-phase applications.

Pharmacological comparison of novel synthetic fenamate analogues with econazole and 2-APB on the inhibition of TRPM2 channels

BACKGROUND AND PURPOSE Fenamate analogues, econazole and 2‐aminoethoxydiphenyl borate (2‐APB) are inhibitors of transient receptor potential melastatin 2 (TRPM2) channels and are used as research tools. However, these compounds have different chemical structures and therapeutic applications. Here we have investigated the pharmacological profile of TRPM2 channels by application of newly synthesized fenamate analogues and the existing channel blockers.

Synthesis of α-heterosubstituted glycine derivatives from dihaloethanamides

Abstract A range of protected α-heterosubstituted analogues of glycine were synthesised from starting materials of the type CHFX-CONHR [X = Cl, Br, I; R = CH 2 Ph, ( S )-CHMePh]; the final products included derivatives of glycine possessing N , O , F or S in the α-position, and the first example of a free α-fluoro-α-amino acid (α-fluorobetaine) whose structure was confirmed by X-ray crystal structure determination.

Sporopollenin as an efficient green support for covalent immobilization of a lipase

Sporopollenin exine capsules (SECs), derived from the spores of Lycopodium clavatum, have been functionalised with 1,n-diamines and the resulting aminoalkyl microcapsules used to immobilize Candida antarctica lipase B (Cal B) via a glutaradehyde-based diimine covalent linker. The supported enzyme efficiently catalyzes the esterification of oleic acid with ethanol. Initial rates using the SEC-CalBs were comparable to the commercial enzyme Novozym 435, but displayed up to 20-fold higher specific activity. The supported enzymes could also be recycled and after four cycles displayed only a modest decrease in conversions. In a kinetic resolution the SEC-CalBs efficiently acetylated rac-1-phenylethanol, with conversions up to 37% after 5 hours and product enantiomeric excesses of >99%. Related to this, the dynamic resolution of rac-1-phenylethylamine, in the presence of Pd–BaSO4 and ammonium formate, led to the acetylated amine with a 94% conversion and >99% ee.