Patent Publication Number: US-2021193272-A1

Title: Method for evaluating synthetic aptitude of compound, program for evaluating synthetic aptitude of compound, and device for evaluating synthetic aptitude of compound

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a Continuation of PCT International Application No. PCT/JP2019/036072 filed on Sep. 13, 2019 claiming priority under 35 U.S.C § 119(a) to Japanese Patent Application No. 2018-172576 filed on Sep. 14, 2018. Each of the above applications is hereby expressly incorporated by reference, in its entirety, into the present application. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method for evaluating a synthetic aptitude of a compound, a program for evaluating a synthetic aptitude of a compound, and a device for evaluating a synthetic aptitude of a compound, and particularly relates to a method for evaluating a synthetic aptitude of a compound, a program for evaluating a synthetic aptitude of a compound, and a device for evaluating a synthetic aptitude of a compound, the compound being generated or modified on a computer. 
     2. Description of the Related Art 
     In the related art, the search for a structure of a compound having a desired physical property value has been performed mainly by giving a molecular structure and obtaining a physical property value as a result, but with the development of informatics in recent years, studies of giving a physical property value and obtaining a molecular structure having the physical property value are rapidly progressing. For example, “Bayesian molecular design with a chemical language model”, Hisaki Ikebata et al., “searched on Jul. 23, 2018”, internet (https://www.ncbi.nlm.nih.gov/pubmed/28281211) is known as a method for searching a molecular structure from the physical property value. The “Bayesian molecular design with a chemical language model”, Hisaki Ikebata et al., “searched on Jul. 23, 2018”, internet (https://www.ncbi.nlm.nih.gov/pubmed/28281211) discloses that a structure having a physical property value close to the target value is obtained by, giving a target value of physical property value, (1) generating a plurality of initial structures (chemical structures), (2) randomly changing each structure, (3) estimating the physical property value of each structure, and (4) adopting or rejecting the change in structure based on the distance between the physical property value and the target value. In this process, the processes (2) to (4) are repeated. As described above, in order to search the molecular structure from the physical property value, a technique for performing (1) to (4) is required. 
     In a case of performing the above-described (1) to (4), since it is meaningless in a case where all of the chemical structures obtained in (4) are difficult to synthesize, a technique capable of evaluating a synthetic aptitude of the compound is required. As such an evaluation method, a technique for calculating a synthetic accessibility score (SAscore) has been known (refer to “Estimation of synthetic Accessibility score of drug-like molecules based on molecular complexity and fragment contributions”, Peter Ertl and Ansgar Schuffenhauer, Journal of Cheminformatics 2009, 1; 8, “searched on Jul. 23, 2018”, internet (https://jcheminf.springeropen.com/articles/10.1186/1758-2946-1-8)). SAscore has an actual value from 1 to 10, and as the value is smaller, it is considered to be synthesized more easily. 
     SUMMARY OF THE INVENTION 
     In SAscore disclosed in the “Estimation of synthetic Accessibility score of drug-like molecules based on molecular complexity and fragment contributions”, Peter Ertl and Ansgar Schuffenhauer, Journal of Cheminformatics 2009, 1; 8, “searched on Jul. 23, 2018”, internet (https://jcheminf.springeropen.com/articles/10.1186/1758-2946-1-8), an atomic arrangement in a compound is extracted, the atomic arrangement is fragmented with a definition based on ECFC_4 # fragments, the logarithm of an appearance frequency of each fragment in a database is used as a contribution of the fragment, and the contributions of each fragment are summed, thereby obtaining a score. However, in the “Estimation of synthetic Accessibility score of drug-like molecules based on molecular complexity and fragment contributions”, Peter Ertl and Ansgar Schuffenhauer, Journal of Cheminformatics 2009, 1; 8, “searched on Jul. 23, 2018”, internet (https://jcheminf.springeropen.com/articles/10.1186/1758-2946-1-8), since relatively large fragments or fragments having a complicated branching structure are considered, half of the extracted fragments are fragments appearing only once in the database. The “appearing only once in the database” means that a specific molecule is an individual fragment, and this result suggests that such a molecule-individual fragment is likely to occur based on the ECFC_4 # fragments. 
     As the extracted fragment is larger, or as the branching structure included in the fragment is more complex, the appearance frequency in the database is smaller. In other words, as the number of bonds included in the fragment is larger, the appearance frequency in the database is smaller. However, such a molecular arrangement may not always be difficult to synthesize, and in some cases, the evaluation of the score with the synthetic aptitude are not performed properly. 
     As described above, in the evaluation of synthetic aptitude using the compound database in the related art, the synthetic aptitude of the compound cannot be sufficiently evaluated. 
     The present invention has been studied in view of such circumstances, and an object of the present invention is to provide a method for evaluating a synthetic aptitude of a compound, a program for evaluating a synthetic aptitude of a compound, and a device for evaluating a synthetic aptitude of a compound, which evaluate a synthetic aptitude of a compound generated and/or modified on a computer in order to efficiently search for a structure of the compound. 
     In order to achieve the object of the present invention, a method for evaluating a synthetic aptitude of a compound according to an aspect of the present invention includes: 
     a step of selecting a compound database storing a plurality of reference compounds which serve as evaluation criteria for a synthetic aptitude; 
     a step of deciding a structure of a compound to be evaluated for the synthetic aptitude; 
     a step of extracting a reference atomic arrangement from a structure of the reference compound stored in the compound database and obtaining a reference appearance frequency of the reference atomic arrangement; 
     a step of extracting an atomic arrangement from the structure of the compound and obtaining an appearance frequency of the atomic arrangement; and 
     a step of evaluating the synthetic aptitude based on the number of bonds included in the atomic arrangement of the compound and the appearance frequency of the reference atomic arrangement corresponding to the atomic arrangement. 
     In order to achieve the object of the present invention, a program for evaluating a synthetic aptitude of a compound according to an aspect of the present invention causes a computer to execute the above-described method for evaluating a synthetic aptitude of a compound. 
     In order to achieve the object of the present invention, a device for evaluating a synthetic aptitude of a compound according to an aspect of the present invention includes: 
     a database selection part of selecting a compound database storing a plurality of reference compounds which serve as evaluation criteria for a synthetic aptitude; 
     a structure acquisition part of acquiring a structure of a compound to be evaluated for the synthetic aptitude; 
     a first extraction part of extracting a reference atomic arrangement from a structure of the reference compound stored in the compound database and obtaining a reference appearance frequency of the reference atomic arrangement; 
     a second extraction part of extracting an atomic arrangement from the structure of the compound and obtaining an appearance frequency of the atomic arrangement; 
     a calculation part of calculating, as a partial score, a frequency with which the atomic arrangement appears in the reference compound, and calculating a total score by totaling the partial scores, based on the number of bonds included in the atomic arrangement of the compound and the appearance frequency of the reference atomic arrangement corresponding to the atomic arrangement, using a function in which a numerical value decreases as the number of bonds included in the atomic arrangement and the appearance frequency increase; and 
     an evaluation part of evaluating the synthetic aptitude based on the total score. 
     With the method for evaluating a synthetic aptitude of a compound according to the aspect of the present invention, the appearance frequency of the atomic arrangement in the compound database, the atomic arrangement being extracted from a compound to be evaluated, is obtained, and the synthetic aptitude is evaluated based μm the number of bonds included in the atomic arrangement and the appearance frequency. By evaluating the synthetic aptitude in consideration of the number of bonds included in the atomic arrangement, the appearance frequency decreases as the number of bonds increases, and the synthetic aptitude of a compound evaluated as having low synthetic aptitude can be evaluated properly. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram showing a configuration of a device for evaluating a synthetic aptitude of a compound. 
         FIG. 2  is a diagram showing a configuration of a processing part. 
         FIG. 3  is a diagram showing information stored in a storage part. 
         FIG. 4  is a flowchart showing a method for evaluating a synthetic aptitude of a compound. 
         FIG. 5  is a structural formula of a compound for which the synthetic aptitude is evaluated in the present embodiment. 
         FIG. 6  is partial excerpts of tables showing extracted reference atomic arrangements and the number of reference appearance frequencies. 
         FIG. 7  is tables showing extracted atomic arrangements of the compound to be evaluated and frequencies of appearance. 
         FIG. 8  is a diagram showing a relationship between a compound and a synthetic aptitude score. 
         FIG. 9  is a diagram showing a relationship between a compound and SAscore. 
         FIG. 10  is a diagram showing a relationship between ChemistScore and a synthetic aptitude score. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, a method for evaluating a synthetic aptitude of a compound, program for evaluating a synthetic aptitude of a compound, and device for evaluating a synthetic aptitude of a compound according to embodiments of the present invention will be described with reference to the accompanying drawings. 
     &lt;&lt;Device for Evaluating Synthetic Aptitude of Compound&gt;&gt; 
       FIG. 1  is a block diagram showing a configuration of a device  10  for evaluating a synthetic aptitude of a compound (hereinafter, also simply referred to as a “synthetic aptitude evaluation device”). The synthetic aptitude evaluation device  10  is a device for evaluating a synthetic aptitude of a compound, and can be realized using a computer. As shown in  FIG. 1 , the synthetic aptitude evaluation device  10  includes a processing part  100 , a storage part  200 , a display part  300 , and an operation part  400 , which are connected to each other to transmit and receive necessary information. Various installation forms can be adopted for these constituents, and each constituent may be installed in one place (one housing, one room, and the like), or may be installed at a distant place and connected through a network. In addition, the synthetic aptitude evaluation device  10  is connected to an external server  500  and an external database  510  through the network NW such as the internet, and can acquire information such as a structural formula of a compound for which the synthetic aptitude is evaluated, and/or structural formulae of a plurality of reference compounds stored in a compound database, as necessary. 
     &lt;Configuration of Processing Part&gt; 
       FIG. 2  is a diagram showing a configuration of the processing part  100 . The processing part  100  includes a database selection part  105 , a structure acquisition part  110 , a first extraction part  115 , a second extraction part  120 , a calculation part  125 , an evaluation part  130 , an output part  135 , a display control part  140 , a central processing unit (CPU)  145 , a read only memory (ROM)  150 , and a random access memory (RAM)  155 . 
     The database selection part  105  selects, from a plurality of compound databases storing a plurality of reference compounds, a compound database storing a compound suitable for the purpose of evaluating a synthetic aptitude. The compound database can be selected from a plurality of compound databases acquired through a recording medium interface such as a DVD drive and a terminal for semiconductor memory (not shown), and/or a network. The compound database to be selected is preferably a compound database having a high structural diversity, and in a case of a special purpose, a compound database having a structural bias according to the purpose can also be selected. For example, in a case where it is required to determine whether or not a compound to be evaluated for a synthetic aptitude is a coloring agent-based compound, a compound database including many compounds which are coloring agents is selected. In addition, in a case where it is required to determine whether or not a compound to be evaluated for a synthetic aptitude is a medicament-based compound, a compound database including many compounds which are medicaments is selected. 
     The structure acquisition part  110  acquires information such as a structural formula of the compound through the recording medium interface such as a DVD drive and a terminal for semiconductor memory (not shown), and/or the network. For information such as a structural formula of the compound, a compound generated and/or modified on a computer can be used. In addition, the structural formula of the compound may be input using a keyboard  410  and mouse  420  of the operation part  400 . 
     The first extraction part  115  extracts a reference atomic arrangement from a structure of the reference compound stored in the compound database, and obtains a reference appearance frequency of the reference atomic arrangement. 
     The second extraction part  120  extracts an atomic arrangement from the structure of the compound for which the synthetic aptitude is evaluated, and obtains an appearance frequency of an atomic arrangement from the compound for which the synthetic aptitude is evaluated. 
     The calculation part  125  calculates, as a partial score, a frequency with which the atomic arrangement appears in the reference compound, based on the number of bonds included in the atomic arrangement of the compound for which the synthetic aptitude is evaluated, and the reference appearance frequency of the reference atomic arrangement of the compound stored in the compound database. In addition, the calculation part  125  totals the partial scores and calculates the total score. 
     The evaluation part  130  evaluates the synthetic aptitude based on the total score calculated by the calculation part  125 . Since the partial score is obtained using a function in which the numerical value decreases as the number of bonds included in the atomic arrangement and the appearance frequency in the compound database increase, it can be evaluated that the synthetic aptitude is higher as the partial score is smaller, that is, the total score is smaller. In addition, in the compound database selected by the database selection part, in a case where a compound database having a structural bias according to the purpose is selected, the similarity between the compound and the reference compound in the compound database can also be evaluated. For example, in a case where a compound database including many compounds which are coloring agents is selected as the compound database, and the total score calculated is small, it can be identified that the appearance frequency of the atomic arrangement is large in the compounds including many compounds which are coloring agents, and it can be evaluated that the similarity is high. As a result, it can be evaluated that the compound to be evaluated has a high possibility of having properties of a coloring agent. 
     The output part  135  outputs the structure of the compound to be evaluated for the synthetic aptitude, which is acquired by the structure acquisition part  110 . In addition, the output part  135  outputs the reference atomic arrangement and appearance frequency of the reference atomic arrangement extracted by the first extraction part  115 , and the atomic arrangement of the compound extracted by the second extraction part  120  and the appearance frequency of the atomic arrangement of the compound. Furthermore, the output part  135  outputs the partial score and total score calculated by the calculation part  125 . 
     The display control part  140  controls display of the acquired information and processing result on a monitor  310 . The method for evaluating a synthetic aptitude of a compound using these functions of the processing part  100  will be described in detail later. The process by these functions is performed under the control of CPU  145 . 
     The function of each part of the processing part  100  described above can be realized by using various processors. Examples of the various processors include a CPU that is a general-purpose processor which executes software (program) to realize various functions. In addition, examples of the various processors also include a programmable logic device (PLD) which is a processor in which circuit configuration can be changed after manufacturing, such as a field programmable gate array (FPGA). Furthermore, examples of the various processors also include a dedicated electric circuit which is a processor having a circuit configuration specifically designed to execute a specific process, such as an application specific integrated circuit (ASIC). 
     The functions of each part may be realized by one processor, or may be realized by combining a plurality of processors. In addition, a plurality of functions may be realized by one processor. As an example of configuring a plurality of functions with one processor, firstly, an aspect that, as typified by a computer such as a client and a server, one processor is configured by a combination of one or more CPUs and software, and this processor realizes the plurality of functions is exemplified. Secondly, an aspect that, as typified by a system on chip (SoC), uses a processor which realizes the functions of the entire system with a single integrated circuit (IC) chip is exemplified. As described above, various functions are composed by using one or more of the above-described various processors as a hardware structure. Furthermore, the hardware structure of these various processors is more specifically an electric circuit (circuitry) in which circuit elements such as semiconductor elements are combined. 
     In a case where the above-described processor or electric circuit executes a software (program), a processor (computer)-readable code of the software to be executed is stored in a non-temporary recording medium such as ROM  150  (refer to  FIG. 2 ), and the processor refers to the software. The software stored in the non-temporary recording medium includes the program for executing the method for evaluating a synthetic aptitude of a compound according to the embodiment of the present invention. The code may be recorded in a non-temporary recording medium such as various magneto-optical recording devices and semiconductor memories instead of ROM  150 . In a case of processing using a software, for example, RAM  155  is used as a temporary storage area, and for example, data stored in an electronically erasable and programmable read only memory (EEPROM) (not shown) can be referred to. 
     &lt;Configuration of Storage Part&gt; 
     The storage part  200  is configured of a non-temporary recording medium such as a digital versatile disk (DVD), a hard disk, and various semiconductor memories, and a control part thereof, and stores images and information shown in  FIG. 3 . Structure information  205  includes the structure of the compound to be evaluated for the synthetic aptitude. Reference compound information  210  includes structural formulae of a plurality of reference compounds stored in the compound database. Atomic arrangement information  215  includes atomic arrangements extracted from the compound to be evaluated for the synthetic aptitude. Appearance frequency Information  220  includes frequencies of appearance of the extracted atomic arrangements in the compound to be evaluated for the synthetic aptitude. Reference atomic arrangement information  225  includes reference atomic arrangements extracted from the plurality of reference compounds included in the compound database. Reference appearance frequency information  230  includes appearance reference frequencies of the extracted atomic arrangements in the plurality of reference compounds included in the compound database. Function information  235  includes a function for calculating the partial score and a function for calculating the total score. 
     &lt;Configuration of Display Part and Operation Part&gt; 
     The display part  300  includes the monitor  310  (display device), and can display the input image and information, the image and information stored in the storage part  200 , the result of process by the processing part  100 , and the like. The operation part  400  includes the keyboard  410  and the mouse  420  as input devices and/or pointing devices, and the user can perform operations necessary for executing the method for evaluating a synthetic aptitude of a compound according to the embodiment through these devices and a screen of the monitor  310 . Operations which can be performed by the user include input the structure of the compound for which the synthetic aptitude is evaluated, selection of the compound database, specification of an atomic arrangement to be extracted, and the like. 
     &lt;Process in Device for Evaluating Synthetic Aptitude of Compound&gt; 
     In the above-described device  10  for evaluating a synthetic aptitude of a compound, a synthetic aptitude of a compound can be evaluated according to the user&#39;s instruction through the operation part  400 . 
     &lt;&lt;Method for Evaluating Synthetic Aptitude of Compound&gt;&gt; 
       FIG. 4  is a flowchart showing the method for evaluating a synthetic aptitude of a compound. The method for evaluating a synthetic aptitude includes: a step (Step S 10 ) of selecting a compound database storing a plurality of reference compounds which serve as evaluation criteria for a synthetic aptitude; a step (Step S 12 ) of deciding a structure of a compound for which the synthetic aptitude is evaluated; a step (Step S 14 ) of extracting a reference atomic arrangement from the reference compound stored in the compound database and obtaining a reference appearance frequency of the reference atomic arrangement; a step (Step S 16 ) of extracting an atomic arrangement from the structure of the compound and obtaining an appearance frequency of the atomic arrangement; a step (Step S 18 ) of calculating, as a partial score, a frequency with which the atomic arrangement of the compound appears in the reference compound in the compound database; and a step (Step S 20 ) of evaluating the synthetic aptitude from a total score obtained by totaling the partial scores. 
     Hereinafter, each step will be described. 
     &lt;Step of Selecting Compound Database (Step S 10 )&gt; 
     The step of selecting a compound database is a step of selecting, from a plurality of compound databases, a compound database which serves as evaluation criteria for a synthetic aptitude. Basically, as the compound database to be selected, a compound database having a high structural diversity is desirable. By selecting a compound database having a high structural diversity, it is possible to evaluate a synthetic aptitude based on various compounds. In addition, in a case where the compound to be evaluated has a special purpose, a compound database having a structural bias according to the purpose may be used. For example, in a case where it is required to determine whether or not the compound is a coloring agent-based compound, a compound database including many known coloring agent compounds can also be selected. In addition, in a case where it is required to determine whether or not the compound is a medicament compound, a compound database including many known medicament compounds can also be selected. As described above, by using a compound database having a structural bias according to a special purpose, it is possible to evaluate whether or not an atomic arrangement appears in the coloring agent compound or medicament compound in the compound database with a high appearance frequency. The case where the appearance frequency is high is considered that the compound to be evaluated has a structure of the reference compound in the selected compound database or a structure close to the atomic arrangement, and is considered that the compound to be evaluated has the same properties as a target compound. 
     The selection of the compound database may be performed according to the operation of the user, or may be configured to select the compound database by the computer according to conditions desired by the user. As an example of the compound database, PubChem can be used. As the reference compound, all the compounds in the compound database may be used for evaluation, or a part, for example, one million compounds, may be extracted and used for evaluation. As a method for extracting the reference compound from the compound database, compounds may be arbitrarily extracted, or compounds according to a purpose may be extracted so that a database according to the purpose is selected. In the present embodiment, PubChem is used as the compound database, and all the compounds in PubChem are used as the reference compound. 
     &lt;Step of Deciding Structure of Compound (Step S 12 )&gt; 
     The step of deciding a structure of the compound is a step of deciding a structure of a compound to be evaluated for the synthetic aptitude. In the compound, a structure of the compound may be input according to the operation of the user through the operation part  400  to decide the structure of the compound. In addition, using a structure of a compound in which a structure has been modified in a computer so that desired physical properties can be obtained, the modified compound can also be decided as the compound to be evaluated for the synthetic aptitude. The structure of the compound may be acquired from the external server  500  and the external database  510  through the network NW to be decided. In the present embodiment, as the compound to be evaluated for the synthetic aptitude, a structure of a compound shown in  FIG. 5  is exemplified. 
     &lt;Step of Extracting Reference Atomic Arrangement and Obtaining Reference Appearance Frequency (Step S 14 )&gt; 
     The step of extracting a reference atomic arrangement and obtaining a reference appearance frequency is a step of extracting a reference atomic arrangement from the reference compound in the compound database selected in the step S 10  and obtaining a reference appearance frequency, which is an appearance frequency of this reference atomic arrangement in the reference compound. 
     The reference atomic arrangement is an atomic arrangement extracted from the reference compound. The atomic arrangement is extracted for each number of bonds. Since the extracted reference atomic arrangement is used in the step (Step S 18 ) of calculating a partial score described later, in the same manner as in an atomic arrangement to be extracted from the compound to be evaluated, at least a reference atomic arrangement corresponding to the atomic arrangement is extracted. For example, the extraction is performed under the same conditions such as the number of bonds from an atom of interest, a structure of the atomic arrangement, and an electronic state of the atom. These conditions are not particularly limited as long as the conditions are the same as in the atomic arrangement extracted from the compound to be evaluated. For example, as the structure of the atomic arrangement, an atomic arrangement having a linear form, a branched form, a cyclic form, or a combination thereof can be extracted. In addition, in a case where electronic states of atoms are different from each other, it is preferable that the reference atomic arrangement and the atomic arrangement are extracted as different atomic arrangements. For example, in a carbon-carbon bond, an SP 1  hybrid orbital, an SP 2  hybrid orbital, and an SP 1  hybrid orbital are preferably extracted as different atomic arrangements. Furthermore, in a bond having a hydrogen atom in an end portion, in a case where a bond with the hydrogen atom does not need to be particularly considered, it is preferable that the extraction is performed such that the number of bonds does not include the bond with the hydrogen atom. Since the appearance frequency increases in a case of including the bond having a hydrogen atom in the end portion, the partial score and total score cannot be evaluated accurately. 
     Next, the reference appearance frequency of the extracted reference atomic arrangement in the reference compound is obtained. The reference appearance frequency is obtained with regard to all of the reference compounds in the compound database selected in the step S 10 , or with regard to the reference compound extracted from the compound database. 
       FIG. 6  is partial excerpts of tables showing extracted reference atomic arrangements and the number of appearance reference frequencies. In the present embodiment, atomic arrangements having a linear form, in which the number of bonds is up to 5, are extracted. 
     Atom names shown in the tables of  FIG. 6  are atoms shown by Tripos Mol2 format. For example, a carbon of sp 1  hybrid orbital is represented by “C.1”, a carbon of sp 2  hybrid orbital is represented by “C.2”, a carbon of sp 3  hybrid orbital is represented by “C.3”, and a carbon constituting an aromatic ring is represented by “C.ar”. In addition, “-” between atoms means a single bond, “=” therebetween means a double bond, “#” therebetween means a triple bond, and “:” therebetween means aromatic. In addition, in the atom names shown in  FIG. 6 , “I” represents an iodine atom, “S.3” represents a sulfur atom of sp 3  hybrid orbital, “N.pl3” represents a nitrogen atom of a trigonal planar structure, and “O.co2” represents an oxygen atom in a carboxylic acid group and a phosphoric acid group. The tables shown in  FIG. 6  show, as an example, a case of one bond (number of bonds is 1) and five bonds (number of bonds is 5), in which an atomic arrangement having the highest appearance frequency, an atomic arrangement having the second highest appearance frequency, and an atomic arrangement having the lowest appearance frequency is included, but in fact, there are many atomic arrangements, and the number of atomic arrangements in one bond is approximately 1 million. Since the reference atomic arrangement is extracted by the number of bonds from the atom of interest and the structure, in one benzene ring of the reference compound, the appearance frequency of “C.ar:C.ar” is “6”, and the appearance frequency of “C.ar:C.ar:C.ar:C.ar:C.ar:C.ar” is “6”. 
     &lt;Step of Extracting Atomic Arrangement and Obtaining Appearance Frequency (Step S 16 )&gt; 
     The step of extracting an atomic arrangement and obtaining an appearance frequency is a step of extracting an atomic arrangement from the structure of the compound input in the step S 12 , and obtaining an appearance frequency. 
     The extraction of the atomic arrangement can be performed in the same manner as the method of extracting the reference atomic arrangement in the step S 16 . In addition, with respect to the extracted atomic arrangement, the appearance frequency in the compound input in the step S 12  is obtained. 
       FIG. 7  is tables showing, with respect to the compound input in the step S 12 , extracted atomic arrangements and frequencies of appearance of the atomic arrangements in the compound. Even in the step of extracting an atomic arrangement and obtaining an appearance frequency, same as in the step S 14 , atomic arrangements are extracted under the conditions that the number of bonds of atoms is 1 to 5, the atomic arrangements have a structure of a linear form, and an atomic arrangement in which the terminal is a bond of a hydrogen atom is not included, and frequencies of appearance are obtained. “-(edge)” in the tables represents that the atom is the terminal of the structural formula. 
     &lt;Step of Calculating Partial Score (Step S 18 )&gt; 
     The step of calculating a partial score is a step of calculating, as a partial score, a frequency with which the atomic arrangement of the compound to be evaluated for the synthetic aptitude appears in the reference compound in the compound database. 
     As an expression (function) for calculating the partial score, a monotonically decreasing function or a monotonically increasing function can be used. As the function, for example, an inverse proportional function, an exponential function, and the like can be used. As the monotonically decreasing function, a function, in which the value decreases as the number (n) of bonds included in the atomic arrangement and/or the frequency (f) of appearance of the atomic arrangement in the reference compound in the compound database increase, can be used. In a case where the number of bonds included in the atomic arrangement increases, the reference appearance frequency in the reference compound decreases. However, in the atomic arrangement with a large number of bonds, there is an atomic arrangement which has a simple structure and is easy to synthesize, but in which the reference appearance frequency is low due to that the number of bonds is large. For example, in a case where the reference compound is propane (CH 3 CH 2 CH 3 ), the appearance frequency of an atomic arrangement of C.3-C.3 is “2”, and the appearance frequency of C.3-C.3-C.3 is “1”. As described above, even in a case of a compound which is easy to synthesize, a difference in synthetic aptitude occurs in a case where the score is calculated from the reference appearance frequency. In the present embodiment, since a function in which the number of bonds included in the atomic arrangement is also considered as a variable is used, the numerical value of the partial score decreases as the number of bonds increases. As a result, it is possible to reduce the influence of a large (the number of bonds is large) atomic arrangement (complex atomic arrangement which tends to be a unique arrangement of molecule) on an atomic arrangement in which the number of bonds is small and the reference appearance frequency is high. Therefore, comparing with a score simply obtained from the appearance frequency, the synthetic aptitude can be evaluated properly. 
     In addition, in a case where the frequency f of appearance is 0, that is, a case where an atomic arrangement extracted from the compound does not appear in the reference compound, it is preferable to use a function having no singular point. The atomic arrangement in which the frequency f of appearance is 0 is considered to be an atomic arrangement which is unlikely to exist as an atomic arrangement of a compound in the related art. Therefore, a compound with such an atomic arrangement should be evaluated as a compound having low synthetic aptitude, but since the score cannot be calculated in a case where a singular point is present at f=0, the contribution from such an atomic arrangement is ignored in the evaluation of synthetic aptitude. As a result, the score may indicate that the compound has the synthetic aptitude, which is a case where the synthetic aptitude is not evaluated properly. By using a function having no singular point at the frequency f of appearance is 0, the synthetic aptitude can be evaluated properly. 
     As a function used for the calculation of the partial score, for example, functions shown by Expression (1) and Expression (2) can be used. 
     
       
         
           
             
               
                 
                   
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     In the expressions, substr is an atomic arrangement included in the compound to be evaluated, and s is a partial score. n is the number of bonds included in the atomic arrangement, and f is a reference appearance frequency in the compound database. d, d n , and d f  are parameters, and by changing the numerical values of d, d n , and d f , the numerical value of s(substr) can be changed. The partial score can be increased by increasing the value of d, and the partial score can be decreased by increasing the values of d n  and d f . In addition, σ n  and σ f  are parameters, and by changing the numerical values of σ n  and σ f , the numerical value of s(substr) can be changed. The partial score can be increased by increasing the values of σ n  and σ f . Expression (1) and Expression (2) are monotonically decreasing functions, and in a case where a monotonically increasing function is used, the interpretation of the obtained score is reversed, that is, it can be determined that the synthetic aptitude is higher as the obtained score is higher. 
     Next, an example of calculating the partial score will be described. As an example, a partial score of C.ar:C.ar (carbon-carbon bond in an aromatic ring) which is an atomic arrangement of one bond will be calculated. As an expression for obtaining the partial score, Expression (1) described above is used. In addition, the parameter d is set to “1”. 
     First, a partial score of the atomic arrangement C.ar:C.ar in the reference compound of the compound database (PubChem) is calculated. Since the appearance frequency of the atomic arrangement C.ar:C.ar in the reference compound of the compound database (PubChem) is 799082034, s(C.ar:C.ar) is 1/(1×(799082034+1))=1.25×10 −9 . 
     Next, based on the partial score of the atomic arrangement C.ar:C.ar in the reference compound of the compound database (PubChem), a partial score of C.ar:C.ar in the compound for which the synthetic aptitude is evaluated is calculated. Since the appearance frequency of C.ar:C.ar in the compound for which the synthetic aptitude is evaluated is “6”, the partial score of C.ar:C.ar in the compound for which the synthetic aptitude is evaluated is 1.25×10 −9 ×6=7.5×10 −9 . 
     In addition, since the appearance frequency of the atomic arrangement Br-O.3-C.ar:C.ar:C.ar:C.ar in the reference compound of the compound database is 670, s(Br-O.3-C.ar:C.ar:C.ar:C.ar) is 1/(5×(670+1))=2.98×10 −4 . Since the appearance frequency of Br-O.3-C.ar:C.ar:C.ar:C.ar in the compound to be evaluated for the synthetic aptitude is “2”, the partial score is 2.98×10 −4 ×2=5.96×10 −4 . 
     As described above, the partial score can be decided by a balance between the number of bonds in the atomic arrangement and the appearance frequency in the reference compound of the compound database. 
     In the step S 18 , partial scores are calculated for all of the atomic arrangements shown in the tables of  FIG. 7 . In  FIG. 7 , the number of bonds is 5 and the atomic arrangement is linear, but depending on the type of an atomic arrangement to be extracted, partial scores of the atomic arrangement are also calculated. 
     &lt;Step of Evaluating Synthetic Aptitude (Step S 20 )&gt; 
     The step of evaluating the synthetic aptitude is a step of evaluating the synthetic aptitude from a total score obtained by totaling the partial scores. 
     The partial scores of the respective atomic arrangements calculated in the step S 18  are totaled to obtain the total score. The total score can be obtained by totaling the partial scores. In a case where, with regard to the compound shown in  FIG. 5 , the partial scores of the respective atomic arrangements shown in  FIG. 7  are calculated and a total score thereof is calculated, the total score is 7.17×10 −3 . 
       FIG. 8  is a diagram in which compounds and synthetic aptitude scores are shown on the horizontal axis. The total score obtained in the step S 18  is the synthetic aptitude score in the present embodiment. It can be evaluated that the synthesis is easier as the synthetic aptitude score is smaller, and it can be determined that the synthesis is more difficult as the synthetic aptitude score is larger. Among compounds A to E shown in  FIG. 8 , the compound D is a compound, as an example of the present embodiment, for which the total score is obtained. The compound A is known for a synthesizable compound, that is, a compound which is stable under the atmosphere at ordinary temperature and pressure and is isolatable. The compound B is known for a compound which is isolatable, but which is unstable under the atmosphere at ordinary temperature and pressure and has no synthetic aptitude. The compounds C to E are known for a compound which also has no synthetic aptitude because the isolation is not possible under the atmosphere at ordinary temperature and pressure. As shown in  FIG. 8 , it can be confirmed that a compound having lower total score (synthetic aptitude score) is more synthesizable and stable. Therefore, by calculating the total score (synthetic aptitude score), the synthetic aptitude of the compound can be evaluated without actually performing the synthesis. It should be noted that, as a parameter is used in a case of calculating the partial score, the total score (synthetic aptitude score) does not perform the evaluation of the synthetic aptitude (easy or difficult to synthesize) at a certain score or higher, but performs the evaluation by comparison with other compounds. 
     In the present embodiment, the partial score is calculated for each of the atomic arrangements to be quantified, and the synthetic aptitude is evaluated by the total score totaling the partial scores. However, the present embodiment is not limited thereto. Instead of quantifying, a partial evaluation may be performed for each of the atomic arrangements, and a total evaluation is performed by totaling the partial evaluations. 
       FIG. 9  is a diagram showing a relationship between SAscore and a compound. It is evaluated that the synthesis is difficult in a case where SAscore is 6 or more. As shown in  FIG. 9 , since the compound B which is unstable and the compounds C to E which are non-synthesizable compounds are in a range in which SAscore is 2 to 3, it is determined that the compounds have the synthetic aptitude. 
     In addition,  FIG. 10  is a diagram showing a relationship between ChemistScore and the total score obtained in the present embodiment. ChemistScore is a score disclosed in “Estimation of synthetic Accessibility score of drug-like molecules based on molecular complexity and fragment contributions”, Peter Ertl and AnsgarSchuffenhauer, Journal of Cheminformatics 2009, 1; 8, “searched on Jul. 23, 2018”, internet (https://jcheminf.springeropen.com/articles/10.1186/1758-2946-1-8), and is a score which is ranked by chemists with regard to the ease of synthesizing a compound. It can be determined that a compound having ChemistScore of 6 or more is difficult to synthesize. As shown in  FIG. 10 , comparing the total score (synthetic aptitude score) obtained in the present embodiment with ChemistScore, in a score equal to or more than the score determined to be difficult to synthesize by ChemistScore, the total score of the present embodiment also determines to be difficult to synthesize. Therefore, it is considered that, as evaluation criteria for the synthetic aptitude, the total score can evaluate the aptitude. 
     &lt;Effects of method for evaluating synthetic aptitude of compound and program for evaluating synthetic aptitude of compound&gt; 
     As described above, using the method for evaluating a synthetic aptitude of a compound and program for evaluating a synthetic aptitude of a compound according to the present embodiment, the device  10  for evaluating a synthetic aptitude of a compound can properly evaluate the synthetic aptitude of the compound, particularly the synthetic aptitude of a compound generated or modified on a computer. 
     Explanation of References 
     
         
         
           
               10 : device for evaluating synthetic aptitude of compound 
               100 : processing part 
               105 : database selection part 
               110 : structure acquisition part 
               115 : first extraction part 
               120 : second extraction part 
               125 : calculation part 
               130 : evaluation part 
               135 : output part 
               140 : display control part 
               145 : CPU 
               150 : ROM 
               155 : RAM 
               200 : storage part 
               205 : structure information 
               210 : reference compound information 
               215 : atomic arrangement information 
               220 : appearance frequency information 
               225 : reference atomic arrangement information 
               230 : reference appearance frequency information 
               235 : function information 
               300 : display part 
               310 : monitor 
               400 : operation part 
               410 : keyboard 
               420 : mouse 
               500 : external server 
               510 : external database 
             NW: network