The effect of phosphate buffer solutions on uniconazole complexation with hydroxypropyl-β-cyclodextrin and methyl-β-cyclodextrin

Strategies To Stabilize Dalbavancin in Aqueous Solutions; Section 3: The Effects of 2 Hydroxypropyl-β-Cyclodextrin and Phosphate Buffer with and without Divalent Metal Ions

PURPOSE

New formulations of the glycopeptide drug dalbavancin containing 2-hydroxpropyl-β-cyclodextrin (2HPβCD) with or without divalent metal ions in phosphate buffer (pH 7.0) were tested to evaluate whether these excipients influence the aqueous solution stability of dalbavancin.

METHOD

Recovery of dalbavancin from phosphate buffered solutions at pH 7.0 with different concentrations of 2HPβCD and a divalent metal ion (Ca2+, Mg2+, or Zn2+) was evaluated by RP-HPLC and HP-SEC after four weeks of storage at 5°C and 55°C. A long-term study of formulations with 2HPβCD and Mg2+ was carried out over six months at 5°C, 25°C, and 40°C using RP-HPLC.

RESULTS

Dalbavancin solutions with either 5.5 mM or 55 mM 2HPβCD were significantly more stable with Mg2+ than with the other divalent metal ions, both at 55°C for four weeks and at 40°C for six months. Dalbavancin was found to be more stable in aqueous solutions at a concentration of 1 mg/mL than at 20 mg/mL with 2HPβCD and Mg2+ at 40°C for six months.

CONCLUSION

The results suggest that 2HPβCD forms an inclusion complex with dalbavancin that slows the formation of the major degradant, mannosyl aglycone (MAG). The effect of 2HPβCD is increased in the presence of Mg2+ and phosphate at pH 7.0, and the complex is more stable at a dalbavancin concentration of 1 mg/mL than at 20 mg/mL. These observations point towards the possibility of formulating a dalbavancin injection solution with a long shelf life at room temperature and physiological pH.

Inclusion Complexes of Rifampicin with Native and Derivatized Cyclodextrins: In Silico Modeling, Formulation, and Characterization

Inclusion complexation of rifampicin (RIF) with several types of cyclodextrins (βCD, hydroxypropyl-βCD, γCD, hydroxypropyl-γCD) in aqueous solutions at different pH values was investigated to assess the interactions between RIF and cyclodextrins (CDs). Molecular modeling was performed to determine the possible interactions between RIF and CDs at several pH values. The inclusion complexes were characterized by differential scanning calorimetry, Fourier transform infrared spectroscopy, powder X-ray diffractometry, and scanning electron microscopy. Moreover, this study evaluated the dissolution profile and antibacterial activity of the formed complexes. Phase solubility analysis suggested the formation of RIF-CD affirmed 1:1 stoichiometry at all pH values (except RIF-βCD at pH 4.0 and both βCD and γCD at pH 9.0). The inclusion complexation of RIF with CD successfully increased the percentage of RIF released in in vitro studies. The inclusion complexes of RIF exhibited more than 60% of RIF released in 2 h which was significantly higher (p < 0.05) than release of pure RIF, which was only less than 10%. Antibacterial activity of RIF-CD complexes (measured by the minimum inhibitory concentration of RIF against Staphylococcus aureus and methicillin-resistant Staphylococcus aureus) was lower for both RIF-βCD and RIF-HPγCD at pH 7.0 to pure RIF suspension. In conclusion, this work reports that both βCD and γCD can be used to enhance the solubility of RIF and thus, improve the effectivity of RIF by decreasing the required daily dose of RIF for the treatment of bacterial infections.

Improved synthetic route of exo-16,17-dihydro-gibberellin A5-13-acetate and the bioactivity of its derivatives towards Arabidopsis thaliana

BACKGROUND

The use of exo-16,17-dihydro-gibberellin A5-13-acetate (DHGA₅ ) in agriculture has been limited by its low synthetic yield. This study was aimed at optimizing the synthetic route of DHGA₅ , designing and synthesizing new derivatives with strong plant growth inhibitory activities.

RESULTS

Previous synthetic methods were replaced with a shorter, milder and faster reaction route with higher yield (76.3%) of DHGA₅ . Based on this novel route, a series of new derivatives were designed and synthesized using DHGA₅ as a lead compound and characterized and evaluated for biological activities in Arabidopsis thaliana. Among the 15 tested derivatives, compound 14j showed a lower medium inhibition concentration (IC₅₀ , 73 μm) in Arabidopsis than that of DHGA₅ (91 μm). Gibberellin deficient mutant assay further revealed that 14j had very different activities compared to DHGA₅ as it specifically inhibits gibberellin biosynthetic pathways. In addition, 14j does not influence the interaction between gibberellin receptors (GID1) and the master growth repressor (RGA) based on yeast two-hybrid assay.

CONCLUSION

The optimized synthetic route provides a promising method for large-scale preparation of DHGA₅ . Our biological assays indicate that 14j likely acts on gibberellin signaling elements other than GID1. These results indicate that novel plant growth regulators can be developed. © 2019 Society of Chemical Industry.

Effect of sulfobutyl ether-β-cyclodextrin and propylene glycol alginate on the solubility of clozapine

Clozapine (CLZ) is an atypical antipsychotic medication used in the treatment of schizophrenia and is poorly soluble in water (0.05 mM). In this study, we have investigated the effect of β-cyclodextrin (CD) and its derivatives on the solubility of CLZ. The solubility of the CLZ was measured to generate a phase solubility diagram, and the interaction between CLZ and sulfobutyl ether-β-cyclodextrin (SBE-β-CD) in aqueous solution was observed by ¹H- and 2D rotating-frame Overhauser enhancement spectroscopy (ROESY)-NMR methods. Moreover, the synergistic effect of SBE-β-CD and water-soluble polymers, including polyvinylpyrrolidone, hydroxypropyl methylcellulose, carboxymethylcellulose sodium salt, polyvinyl alcohol, sodium alginate, and propylene glycol alginate (PGA), on the solubility of CLZ was investigated. The results show that the solubility of CLZ with 1 w/v% PGA was 7.6 mM, which was almost four times greater than that of CLZ without PGA in a 15 mM SBE-β-CD solution. In contrast, the solubility of CLZ with 1 w/v % PGA in an aqueous solution decreased by one-third relative to that of CLZ in a 15 mM SBE-β-CD solution. 2D ROESY-NMR indicated that a CLZ/SBE-β-CD/PGA ternary complex formed. It was found that the combination of PGA and SBE-β-CD enhanced the solubility of CLZ.

Synthesis of Gibberellic Acid Derivatives and Their Effects on Plant Growth

A series of novel C-3-OH substituted gibberellin derivatives bearing an amide group were designed and synthesized from the natural product gibberellic acid (GA₃). Their activities on the plant growth regulation of rice and Arabidopsis were evaluated in vivo. Among these compounds, 10d and 10f exhibited appreciable inhibitory activities on rice (48.6% at 100 μmol/L) and Arabidopsis (41.4% at 100 μmol/L), respectively. These results provide new insights into the design and synthesis of potential plant growth regulators.