Dragon is an application for the calculation of molecular descriptors. Dragon descriptors can be used to evaluate molecular structure-activity or structure-property relationships, as well as for similarity analysis and highthroughput screening of molecule databases.
The first release of Dragon dates back to 1997. Updates and inclusions of new molecular descriptors are regularly made in order to advance research in QSAR and drug design.
Dragon has been designed to run on both Windows and Linux systems and on a variety of computers.
Dragon can run either interactively or in batch mode by a command line.
Dragon provides almost 5,000 molecular descriptors that are divided into 29 logical blocks, each in turn divided into a number of sub-blocks to allow easy retrieval of the molecular descriptors of interest. The user can calculate not only the simplest atom types, functional group and fragment counts, but also several topological and geometrical descriptors. Some molecular properties such as logP, molar refractivity, number of rotatable bonds, H-donors, H-acceptors, molecular volume and surface areas are also calculated by using some common models taken from the literature. Moreover, Lipinski's alert (also known as "the rule of 5") together with some drug-like and lead-like indices are provided to allow selection of compounds for biological screening and/or design of combinatorial libraries.
To calculate molecular descriptors, Dragon requires molecular structure files, which need to be previously generated by other specific chemical drawing programs. The most common molecular file formats are accepted.
To make full use of Dragon calculations, 3D optimised structures with hydrogens are required. However, Dragon can also deal with H-depleted molecules and 2D-structures; in this case, it's clear that some restrictions to descriptor calculation will be applied.
Most of the common organic and inorganic compounds, both charged and uncharged, are correctly processed. Dragon cannot process disconnected structures such as salts. For molecules containing atoms, for which some physicochemical properties are undefined, only the molecular descriptors that do not depend on these atomic properties can be calculated.
Dragon was not designed as QSAR software; it provides only molecular descriptors. However, Dragon permits to merge calculated molecular descriptors and user-defined properties for a set of molecules, providing a complete output file that can be easily loaded by any correlation analysis application. Moreover, a menu has been included in Dragon, which allows calculation of pair correlations between molecular descriptors and experimental properties and performs preliminary SAR investigation through Principal Component Analysis (PCA), allowing the graphical analysis of the distribution of molecules in the structural and response space.
In this section some suggestions will be presented regarding the general work-flow of operations operations that can be carried out by Dragon.
On-line information about Dragon software is given at the web site http://www.talete.mi.it/products/dragon_description.htm