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Schr?inger provides accurate, reliable, and high performance computational technology to solve real-world problems in pharmaceutical, biotechnology, and materials science research. Schr?inger provides accurate, reliable, and high performance computational technology to solve real-world problems in pharmaceutical, biotechnology, and materials science research.
Overview/Features
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Overview
  Epik: Rapid and robust pKa predictions
Combining the proven reliability of Hammett and Taft methods with powerful tautomerization tools, Epik is the program of choice for accurate enumeration of ligand protonation states in biological conditions.


The Advantages of Empirical pKa Prediction

Proper treatment of ligand protonation states is essential to lead discovery. The pKa's of a drug's various functional groups play a critical role in determining its bioavailability and pharmacokinetic profile, while virtual screening software relies on correctly protonated structures in order to perceive the discrete interactions that drive ligand binding. However, many readily available libraries provide ligand structures in familiar tautomeric forms with all functional groups neutralized. These forms may not be highly populated under biological conditions, and are therefore inappropriate for property prediction or virtual screening experiments.

Epik provides a time-tested solution to these problems, designed specifically to work within the context of contemporary drug discovery workflows. Using Hammett and Taft methods in conjunction with ionization and tautomerization tools, Epik is able to rapidly and reliably predict pKa values and return all chemically sensible structures.

Maleic hydrazide is commonly represented as a dione, shown in the top left corner of the above figure. However, the dione tautomerizes to the more stable alcohol shown here, which subsequently undergoes deprotonation in water. Because Epik iteratively tautomerizes and ionizes, it is able to correctly identify this acidic hydrogen and remove it from the output structure.  Epik predicts its pK<sub>a</sub> to be 5.28, which is in good agreement with the experimentally determined pK<sub>a</sub> of 5.67.
Maleic hydrazide is commonly represented as a dione, shown in the top left corner of the above figure. However, the dione tautomerizes to the more stable alcohol shown here, which subsequently undergoes deprotonation in water. Because Epik iteratively tautomerizes and ionizes, it is able to correctly identify this acidic hydrogen and remove it from the output structure. Epik predicts its pKa to be 5.28, which is in good agreement with the experimentally determined pKa of 5.67.
   Features
 
Support for multiple output structures: While other software may only be capable of returning a single structure or pKa value, Epik can return pKa values and 3D structure files for multiple tautomers and ionization states that are likely to exist under the specified conditions.
Tautomeric optimization: Epik is distinguished by its ability to treat tautomeric states without user intervention, an invaluable feature when processing millions of ligands.
Multiple solvent choices: Epik is parameterized to return accurate pKa values in both water and DMSO.
Multiple prediction modes: For maximum speed, Epik can predict pKa's for a structure file in its supplied state. For maximum accuracy, Epik can vary the tautomeric and ionization states if necessary.
LigPrep integration: With a single click, Epik can automatically be employed by LigPrep to enumerate tautomers and protonation states.
Easy-to-use interface: A streamlined standalone interface makes it trivial to set up calculations and interpret results.
Cross-platform support: Epik supports Linux and SGI, and features distributed processing to expedite predictions for large numbers of compounds.
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