Synthesis planning programs

The first task can be done very conveniently with the available reaction retrieval systems. The second task is either a synthesis retrieval or a S3mthesis proposal task. The reaction retrieval systems cannot yet handle the synthesis retrieval job, but the synthesis proposal task can be done with one of the synthesis planning programs. 

Overall, the acceptance of such synthesis planning programs up to now has remained rather low, considering all the progress that has been made in the development of such programs [ 1,11 ] There remains the task to improve the interface of these programs to make them really attractive in the future and to maximize their potentials. 

In this paper we describe how the ORAC reaction database system has been integrated with the LHASA synthesis planning program. This interface allows literature precedents for synthetic steps proposed by LHASA to be retrieved from ORAC and displayed to the user. The problem of sequence searching in reaction database systems is also explored and approaches to this problem are described. Finally, the potential use of synthesis planning systems to identify and classify links between reactions in ORAC for use during sequence searching is considered. 

The primary purpose of a reaction database system is to provide quick and easy access to the reaction literature. Users of synthesis planning programs have a need for such access to the literature in elaborating routes suggested by an analysis. An interface between LHASA and ORAC has recently been developed to provide such a link. The interface allows literature precedents for synthetic steps proposed by LHASA to be retrieved automatically from ORAC s database of over 120,000 reactions and to be displayed to the user on an ORAC Display Form. Company databases can also be accessed to search and display in-house preparative methods and processes in conjunction with databases supplied by ORAC Ltd. 

We can further subdivide implicit scheme searches into two categories. If the eocact product of one reaction is used as the reactant in another reaction, then the connection between the two reactions is by exact-structure, and is referred to here as a first-order imphcit sequence. If the connection between the two reactions is by inexact structure match (such as two highly similar molecules), then we refer to it as a second-order implicit sequence. This latter type of search has much in common with synthesis planning programs it has the most to offer, but poses the greatest technical challenge. 

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