Development of fully-automated synthesis systems

This paper describes the development of fully-automated synthesis systems for preparing and isolating various kinds of pharmaceutical compounds. The systems are versatile, and are able to perform most of the chemical reactions currently used in organic chemistry, with the exception of hydrogenation which requires high pressure. An additional benefit is the very user-friendly software.


Introduction
Pharmaceutical chemists have to carry out extremely routine tasks, such as optimizing reaction conditions and synthesizing many derivatives on the several hundred milligram scale for determining biological activity at the early stage of screening. To release chemists from these time-consuming tasks, the authors have been developing automated synthesis systems equipped with an artificial intelligence (see table 1). With the first system, over 200 derivatives of substituted N-(carboxyalkyl)amino acids [1][2][3][4] were synthesized. The design of this first-generation system was based on a one-way operating system from the mixing of reactants to the isolation of products. This paper reports on improved second and third generation systems. They consist of modular units, which can be operated together or independently (see figure 1), and are controlled with user-friendly software.  b) pH-adjustment device: flask fitted with a pH electrode to measure the pH of a product solution. c) Reaction unit: two flasks with thermostatic jackets, condensers and stirrers; one flask with a condenser, stirrer and an oil-bath. d) Extraction/separation-funnel device: glass funnel fitted with an electric sensor to allow separation of organic and aqueous phases. e) Drying-tube device: for removing water from organic phases by passing them through a drying agent (for example NaaSO,). (f) Temperature control unit: a circulation system with hot and cold fluids for the reaction flasks and condensers.
(g) Washing-exhaust/drainage unit: wash solvent reservoirs, a diaphragm pump and drainage vessel to enable complete washing of the apparatus after each run.
(h) Purification unit: a HPLC device and a fraction collector device.
(i) Reaction monitor unit: for real-time sampling and HPLC analysis.
Design and construction of the hardware General features The automated system is composed of a computer control and synthesis components. The latter comprises units for performing various tasks, such as the supply of reagents and solvents, the control of reaction conditions and the purification of products. The latest synthesis system is   Reaction unil and pH adjustment device Figure 5 shows the main reaction unit, of three reaction flasks, and the pH adjusting device. Two reaction flasks, RF1 and RF2, and the pH adjusting flask (PH) have jackets through which the heating/cooling fluid of ethylene glycol is circulated. The reaction temperatures are thermostatically controlled by regulating the flow of either hot or cold fluid. The reaction flask, RF3, is equipped with an oil bath and a regulated heating element so that it can be heated up to 200C. Its temperature is set freely by keyboard input through an RS232C port.
All these flasks (RF I-RF3, PH) are approximately 100 ml in volume but can be replaced with other sizes of flask. They are equipped with a magnetic or mechanical stirrer, and are connected with each other to allow solutions to be transferred between them. The flow lines are equipped with G-L sensors to check the beginning and the completion of the liquid flow out of the flasks. Concentration ofsolutions can be pertbrmed in RF 1, RF2, and RF3 by heating and bubbling with an inert gas (argon or nitrogen) at the same time. A concentration sensor, which detects the completion of evaporation by tracing the vapour temperature with a thermocouple K(CA), is also attached.

Extraction-drying unit
The unit consists of a separation funnel (SF) equipped with a liquid-liquid sensor (L-L sensor, LL), two solution reservoirs (SR0 and SR1), and five drying tubes (DTI-DT5, 50 ml), see figure 6.
The reaction mixtures can be transferred from any of the reaction flasks (RF) to the SF under reduced pressure.
Extraction and washing is performed either by stirring vigorously in the RF or by bubbling in the RF or SF. Separation of two immiscible liquid phases, formed after extraction or washing ofa reaction mixture, is accomplished by using the L-L sensor to measure the electroconductivity of the two different phases. The lower layer is transferred to either SR0 or SR1. The organic solutions extracted can then be dried by being passed through one of the drying tubes which are prefilled with desiccant such as anhydrous sodium sulphate. To select the drying tube, a position select rotary valve (E1E-023, Uniflows Co., Ltd, Japan) is employed. The L-L sensor is a simple, but highly sensitive, device which can measure the relative electroconductivity of liquids. The difference between the conductivity in the  Purification and monitoring units Figure 7 shows (0"5 ml) is sucked from any of the reaction flasks (RF1, RF2 or RF3). It is then diluted to 10ml with an appropriate solvent stocked in the corresponding RS, stored in SR2, and injected into the analytical HPLC in order to monitor the reaction.
HPLC data and the chromatogram of both preparative and monitoring procedures are printed out and saved on a floppy disk.
Additional service units (R) solenoid valve (24 V); RV rotary valve; DT drying tube; @ manual three-way valve. dried after each run. The ventilation lines of the apparatus are connected to an exhaust duct and the vapour is condensed by a cold trap so that it does not escape into the atmosphere.

Computer control system
The construction of the computer system and interfaces is shown in figure 9. An NEC PC-9801 series (16 or 32 bit CPU, with an 80-120 MB hard disk) was used as the control system. An I/O expansion unit (PC-9811L, NEC, Japan), consisting of an Intelligent AD-converter (AD12-16S(98)H, CONTEC Co. Ltd, Japan), an input/output board (PIO-24/24(98), CONTEC)and three output boards (PO-48(98), CONTEC), is connected to the main CPU. This expansion unit connects each interface board to the synthesis apparatus in order to register signals from the detectors and sensors via input lines, and to operate the various solenoid valves and relays via output lines. The AD12-16S(98) input board receives signals from the L-L sensor, the UV detectors, the pH meter and the concentration sensors. The input/output board receives signals from 20 photosensors, and the output boards send signals to 160 switches of the synthesis apparatus. An RS232C port is used for the exchange of signals between the CPU and the apparatus in order to control the temperature of the reaction flasks.
The apparatus includes an auto/manual changeover  A/M auto/manual changeover switch; SWP switch panel.  Transport liquid in RR to RFs (x 1-3, y= 1; x=4-6, y=2;x= 7-9, y=3) Transport liquid in RFx to RFy(x 1, y=2,3;x=2,y= 1,3;x=3,y= 1,2) Transport liquid in RFx to PH (x 1-3) Transport liquid in PH to RF (x 1, 3) Transport liquid in RF to SRs (x 1, 3, Transport liquid in RF to SF (x 1-3) Transport liquid in SF to RFx (x 1-3) Transport liquid in SF to SR (x 0, 1) Transport liquid in SRx to SF (x 0, 1) Transport liquid in SF by half to RF and RFy (x,y combination of two out ofl,    (see table 2). For the reaction work-up procedure, the user can modit, or create an extraction module by choosing from the extraction subroutine pool, which has about 60 subroutines (see table 3).
There are five main programs (MAKE, REFORM, SIMU, RUN and CHART) comprising about 25000 lines in total (see figure 10). The programs are led by menu screens, so they are user-friendly.
The user composes a reaction program by using MAKE, arranges with REFORM, and simulates with SIMU.
RUN is used to run the apparatus. When 'START' is chosen as the first subroutine, the parameters for the run can be input (volume, temperature, time, pH, HPLC conditions etc.); the parameters can be saved on a floppy disk and used for the next run. START has a self-diagnosis function--it defines the initial state of the apparatus by checking the sensors and warns the user if any of them is in a wrong position. During operation, the user can freely interrupt the procedure or renew the parameters, either from function keys or from manual operation units.   The automated synthesis systems described are capable of running continuously 24 hours a day preparing various kinds ot7 organic compounds. They can perform most of the common organic reactions used in the pharmaceutical industry that do not require the use of high pressures or the automated handling of solids. The menu system used tbr operation means that it is easy for users to compose or modit/ a program and to operate the synthesizing systems.
Details of the synthesis projects performed with these systems will be published in future papers.