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Orally administered drugs primarily enter the systemic circulation via passive diffusion through the intestinal membranes. The drug's absorption is influenced by drug stability in the gastrointestinal GI tract, membrane permeability, the surface area available for absorption, luminal drug concentration, and residence time in the lumen. Drug permeability can be enhanced by adjusting the lipophilicity, polarity, or molecular size of the drug, promoting its passive transport across intestinal...
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Pharmaceutical Alternatives: Polymorphic Form-Related and Particle Size-Related Therapeutic Nonequivalence01:27

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Changes in polymorphic forms can significantly influence the bioavailability of poorly soluble drugs. Although the FDA defines pharmaceutical equivalence based on having the same active ingredient, dosage form, and route of administration, it does not automatically disqualify products with different polymorphic forms. This means two products with different polymorphs can still be deemed pharmaceutically equivalent. However, polymorphic differences can affect properties like wettability,...
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Stability of Substituted Cyclohexanes02:30

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This lesson discusses the stability of substituted cyclohexanes with a focus on energies of various conformers and the effect of 1,3-diaxial interactions.
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Development of a Backbone Cyclic Peptide Library as Potential Antiparasitic Therapeutics Using Microwave Irradiation
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Flexibility versus Rigidity for Orally Bioavailable Cyclic Hexapeptides.

Daniel S Nielsen1, Rink-Jan Lohman1, Huy N Hoang1

  • 1Division of Chemistry and Structural Biology, University of Queensland, Brisbane, QLD, 4072, Australia.

Chembiochem : a European Journal of Chemical Biology
|September 5, 2015
PubMed
Summary

Rigid cyclic peptides, unlike flexible ones, show better membrane permeability and oral bioavailability. This is due to reduced polar surface exposure and lower entropy penalties when moving between environments.

Keywords:
NMR spectroscopycyclic peptidesoral bioavailabilitypeptidespermeability

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Area of Science:

  • Medicinal Chemistry
  • Structural Biology
  • Pharmacology

Background:

  • Cyclic peptides and macrocycles offer potential for membrane permeability and oral bioavailability.
  • These molecules often do not adhere to the established 'rule of five' guidelines for oral drug discovery.

Purpose of the Study:

  • To compare the solvent-dependent 3D structures of three cyclic hexapeptides.
  • To correlate structural properties with membrane permeability, metabolic stability, and oral bioavailability.

Main Methods:

  • Analysis of solvent-dependent three-dimensional structures.
  • Comparison of cyclic hexapeptides containing d-amino acids, prolines, and intramolecular hydrogen bonds.

Main Results:

  • Conformational rigidity, not flexibility, correlated with enhanced membrane permeability.
  • Rigid structures also exhibited improved metabolic stability and oral bioavailability.
  • Reduced polar surface exposure and lower entropy penalties were observed in rigid conformations.

Conclusions:

  • Conformational rigidity is a key factor for improving oral bioavailability and membrane permeability in cyclic peptides.
  • Structural properties, such as reduced solvent-exposed surface area, are critical for drug-like characteristics.