A review on natural sweeteners, sweet taste modulators and bitter masking compounds: structure-activity strategies for the discovery of novel taste molecules

Growing demand for the tasty and healthy food has driven the development of low-calorie sweeteners, sweet taste modulators, and bitter masking compounds originated from natural sources. With the discovery of human taste receptors, increasing numbers of sweet taste modulators have been identified through human taste response and molecular docking techniques. However, the discovery of novel taste-active molecules in nature can be accelerated by using advanced spectrometry technologies based on structure-activity relationships (SARs). SARs explain why structurally similar compounds can elicit similar taste qualities. Given the characterization of structural information from reported data, strategies employing SAR techniques to find structurally similar compounds become an innovative approach to expand knowledge of sweeteners. This review aims to summarize the structural patterns of known natural non-nutritive sweeteners, sweet taste enhancers, and bitter masking compounds. Innovative SAR-based approaches to explore sweetener derivatives are also discussed. Most sweet-tasting flavonoids belong to either the flavanonols or the dihydrochalcones and known bitter masking molecules are flavanones. Based on SAR findings that structural similarities are related to the sensory properties, innovative methodologies described in this paper can be applied to screen and discover the derivatives of taste-active compounds or potential taste modulators.

Modification of Drug Crystallization by Cyclodextrins in Pre-formulation Study

Controlling drug crystallization is one of the important issues in pre-formulation study. In recent years, advanced approaches including the use of tailor-made additives have gathered considerable attention to control crystallization behavior of drugs. This review focuses on the use of hydrophilic cyclodextrins (CDs) as additives for controlling drug crystallization. CDs affect the crystallization of drugs in solution and in solid state based on a host-guest interaction. For example, 2,6-di-O-methyl-β-CD and 2-hydroxybutyl-β-CD suppressed solution-mediated transition of drugs during crystallization by the host-guest interaction; as a result, metastable forms selectively precipitated in solution. The use of CDs in crystal engineering provided an opportunity for the detection of a new polymorph by changing the crystallization pathway. It was also possible to modify crystal morphology (i.e., crystal habit) by selective suppression of crystal growth on a certain direction based on the host-gust interaction. For solid formulation, stable amorphous drug/CDs complex under humid conditions was prepared using two different CDs. An overview of some recent progress in the use of CDs in crystal engineering and in amorphous formulation is described in this review.

Application of Pickering Emulsion with Cyclodextrin as an Emulsifier to a Transdermal Drug Delivery Vehicle

The emulsion prepared with β-cyclodextrin as an emulsifier (βCDE) is considered to be a Pickering emulsion. We examined the characteristics of βCDEs using captopril (CP) as a model drug, and studied the in vitro skin permeation of CP from βCDEs through hairless mouse skin. The stability of βCDE was increased with increasing βCD concentration and conversely decreased with increasing CP concentration. The yield stress value from the rheological measurement results was suggested to be one of the factors determining the stability of the βCDE, and βCDEs with higher yield stress values were more stable. We found that the skin permeability of CP could be improved by using βCDE with isopropyl myristate as the oil phase and that the flux of CP depended on the free CP concentration in the water phase of βCDE.

Ternary inclusion complex formation and stabilization of limaprost, a prostaglandin E1 derivative, in the presence of α- and β-cyclodextrins in the solid state

Limaprost/α-cyclodextrin (CD)/β-CD ternary inclusion complex was prepared by freeze-drying a solution containing all three components. Under humid conditions, limaprost was more stable in the ternary α-/β-CD inclusion complex than in the binary α- or β-CD complex. Specifically, during storage at 30°C/75% relative humidity (R.H.) for 4 weeks, about 19% of limaprost degraded into 17S,20-dimethyl-trans-Δ(2)-prostaglandin A1 (referred as 11-deoxy-Δ(10)) in the β-CD complex, 8.1% degraded in the α-CD complex, and only 2.2% degraded in the α-/β-CD complex. The mechanism of limaprost stabilization in the presence of both CDs was investigated by Raman and solid-state NMR spectroscopy and powder X-ray diffractometry. The fast degradation of limaprost to 11-deoxy-Δ(10) in the β-CD complex was due to the rapid crystallization of β-CD from the complex, liberating the free amorphous drug, which is susceptible to degradation. The dissociation and crystallization of β-CD from the inclusion complex were suppressed by freeze-drying limaprost in the presence of both α- and β-CDs. In addition, the interaction between limaprost and the two CDs was reinforced by inclusion of different moieties of limaprost: α-CD predominantly included the alkyl ω-chain, whereas β-CD included the five-membered ring. Thus, a stable ternary inclusion complex was formed that included limaprost, maintaining the amorphous state of the complex and dramatically stabilizing the drug under humid conditions.

Spectral, thermal, and molecular modeling studies on the encapsulation of selected sulfonamide drugs in β-cyclodextrin nano-cavity

In the present work the inclusion complexation of three sulfonamide (SA) drugs, namely sulfisoxazole (SSX), sulfamethizole (SMZ), and Sulfamethazine (STM) with β-cyclodextrin (β-CD) has been investigated using UV-Vis spectroscopy, DSC, (1)H NMR spectroscopy, and molecular modeling methods. The binding constant (Kb) of SA:β-CD inclusion complexation was determined via applying the modified form of Benesi-Hildebrand equation employing the changes in absorbance at λmax. Obtained results revealed that SA drugs form 1:1 inclusion complex with β-CD with Kb of 650, 1532, 714M(-1) at 25°C for SSX, SMZ, and STM, respectively. The UV-Vis absorption spectra displayed solvatochromic behavior of bathochromic shift with decreasing solvent polarity that in turn is good agreement with their behavior in the presence of β-CD in terms of environment polarity dependency. The inclusion complex formation between β-CD and tested SA drugs in liquid and solid states was confirmed by (1)H NMR and DSC, respectively. Using semi-empirical quantum chemistry methods at PM3 theoretical level, inclusion complexes' structures as well as energetic and thermodynamic parameters of encapsulation were elucidated. Obtained results revealed that the encapsulation is favorably energetic and enthalpic in nature with the inclusion of the aniline moiety through the wide rim side of β-CD nano-cavity. Further, molecular modeling revealed that β-CD encapsulation of SA drugs reduced their (EHOMO-ELUMO) gap.

The formation of host-guest complexes between surfactants and cyclodextrins

Cyclodextrins are able to act as host molecules in supramolecular chemistry with applications ranging from pharmaceutics to detergency. Among guest molecules surfactants play an important role with both fundamental and practical applications. The formation of cyclodextrin/surfactant host-guest compounds leads to an increase in the critical micelle concentration and in the solubility of surfactants. The possibility of changing the balance between several intermolecular forces, and thus allowing the study of, e.g., dehydration and steric hindrance effects upon association, makes surfactants ideal guest molecules for fundamental studies. Therefore, these systems allow for obtaining a deep insight into the host-guest association mechanism. In this paper, we review the influence on the thermodynamic properties of CD-surfactant association by highlighting the effect of different surfactant architectures (single tail, double-tailed, gemini and bolaform), with special emphasis on cationic surfactants. This is complemented with an assessment of the most common analytical techniques used to follow the association process. The applied methods for computation of the association stoichiometry and stability constants are also reviewed and discussed; this is an important point since there are significant discrepancies and scattered data for similar systems in the literature. In general, the surfactant-cyclodextrin association is treated without reference to the kinetics of the process. However, there are several examples where the kinetics of the process can be investigated, in particular those where volumes of the CD cavity and surfactant (either the tail or in special cases the head group) are similar in magnitude. This will also be critically reviewed.