Subgoal transforms

In summary, adding simple reactions to LHASA is simple. Incorporating sophisticated reactions can be as complicated as you wish to make it. (Work is currently underway to prepare a general package of subgoal transforms which will serve to remove interferences - relieving the chemist from having to work them out separately for each super transform.)... 

Structural subgoals may be useful in the application of transform-based strategies. This is especially so with structurally complex retrons which can be mapped onto a target in only one or two ways. It is often possible in such cases quickly to derive the structure of a possible intermediate in a trial retrosynthetic sequence. For instance, with 109 as TGT the quinone-Diels-Alder transform is an obvious T-goal. The retron for that transform can readily be mapped... 

All ring chemistry tables are organized into what is called binary search trees. Queries are posed about the existence of certain structural features. Each of these questions is answerable with a yes or a no. Based on the answer one of two different followup questions is selected. Embedded within the table may be requests for subgoals, either those already in the PGI or PGA table or for special reactions which are needed only for these transforms and are not of general synthetic interest. 

The structure of the search space is determined not only by the collection of transforms available to the system but also by the rules for selecting the transforms to be tried for any subgoal. There are two basic ways for selecting transforms. 

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