[Logo] Centre for Molecular and Biomolecular Informatics
Radboud University Nijmegen


LHASA (Logic and Heuristics Applied to Synthetic Analysis) is a program for synthesis planning, an expert system to assist chemists in designing efficient routes to target molecules for organic synthesis. Operating differently from reaction retrieval systems, LHASA searches its own way in synthesizing known and unknown compounds, using a chemical knowledge base (rather than a database of literature examples). Since LHASA operates in a rigorously retrosynthetic fashion, the knowledge base contains information about retro-reactions (or transforms) rather than reactions. The current version of LHASA (20.3) contains 2271 transforms and 495 so-called tactical combinations.

The program is very user-friendly and almost all communication proceeds via the graphics interface. Consequently, using LHASA does not require prior computer experience. The user draws in a target molecule and indicates a strategy for the retrosynthetic analysis. The program then searches the transform knowledge base for those that satisfy the strategy selected, decides which transforms are appropriate for the particular target structure, and displays the resulting precursors to the chemist. The chemist may then select a precursor for further analysis and choose another strategy option, upon which the program returns a second level of precursors in the same way. Processing continues in this manner until the chemist is satisfied that one or more of the precursors correspond to a reasonable starting point for a synthesis.

[LHASA icon] A typical precursor display from a LHASA session.
Click on image for full display

A useful facility accompanying the LHASA program is the TreePlot program. As the name suggests, TreePlot plots the tree - that is, it creates either a PostScript or an HPGL file. The program is simply called with the tree file as argument.

Documentation is available in:
LHASA Help Facility (users)
LHASA Users' Guide (users)
LHASA Transform Writers' Guide (transform writers)
LHASA CHMTRN Manual (transform writers)

A more extensive (and more technical) description of LHASA is available. You may also wish to visit the LHASA Group Home Page at Harvard University.

The program is being continuously developed by the LHASA Group at Harvard University, in cooperation with the collaborative groups of LHASA Ltd (at Leeds University).

Dr. Alan K. Long
LHASA Project Director
1414 Massachusetts Ave., Room 430
Cambridge, MA 02138

Page author: Martin Ott Last update: Wednesday, 27 October 2004