Automated Chemical Synthesis Controlled by Computer Generated ProgramsPolypeptidesA. M. Tometsko, J. Garden II, and J. Tischio Citation: Review of Scientific Instruments 42, 331 (1971); doi: 10.1063/1.1685087 View online: http://dx.doi.org/10.1063/1.1685087 View Table of Contents: http://scitation.aip.org/content/aip/journal/rsi/42/3?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Establishing a quality control program for an automated dosimetry system Med. Phys. 26, 1732 (1999); 10.1118/1.598665 Computer generation of chemical structures using the gem program AIP Conf. Proc. 330, 544 (1995); 10.1063/1.47757 MIT to offer summer programs in computer sound synthesis and music composition J. Acoust. Soc. Am. 67, 1834 (1980); 10.1121/1.384270 Computer Program for Automatic Composition and Generation of Music J. Acoust. Soc. Am. 35, 1908 (1963); 10.1121/1.2142796 Computer Program to Generate Acoustic Signals J. Acoust. Soc. Am. 32, 1493 (1960); 10.1121/1.1935147

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THE REVIEW OF SCIENTIFIC INSTRUMENTS VOLUME 42, NUMBER 3 MARCH 1971

Automated Chemical Synthesis Controlled by Computer Generated Programs-Polypeptides*

A. M. TOJlETSKO, J. GARDEN, II, AND J. TISCHIO

Department of Biochemistry, University of Rochester Medical Center, Rochester, N f/W York 14620

(Received 16 March 1970; and in final fonn, 28 August 1970)

Instrumentation for the automated chemical synthesis of polypeptides controlled by computer generated paper tape programs is described. The automatic chemical reaction system (ACRS) translated binary coded commands from the paper tape into physical operations resulting in the synthesis of a model polypeptide. The commands for the entire synthesis were generated by computers. Using our computer programs for the synthesis of polypeptides, it is necessary only to specify the amino acid sequence and the computer will set up the appropriate sequence of physical operations (wash cycles, stirring, filtration steps, amino acid additions, etc.) to carry out the synthesis of the desired amino acid sequence. The computer could also automatically make adjustments in the synthetic approach to accommodate the unique problems involved in coupling different amino acids.

INTRODUCTION

THE development of classical approaches in polypep-tide synthesis in recent years has resulted in the

chemical synthesis of a protein, insulin. Inherent in the chemical synthesis of proteins are large numbers of chemi­cal operationsH requiring a considerable amount of time and attention. During the last decade the Merrifield method5 of solid phase peptide synthesis has been applied in the synthesis of a number of polypeptides6- s and has been extended to protein synthesis.9 This approach to the synthesis of polypeptides has been discussed extensively.lO,1l Recently, the automation of solid phase polypeptide syn­thesis has been undertaken in a number of laboratories.1z-

16

Research in this laboratory has been directed toward the development of computer oriented automation techniques that could be applicable to solid phase peptide synthesis presently with a potentially wider applicability to general chemical synthesis. The developed method essentially divides a chemical synthesis into two categories: (1) physical operations such as stirring reactions, measuring volumes, adding chemicals, filtering, etc., and (2) chemical operations such as coupling amino acids, removing pro­tective groups, etc. In order to carry out the physical operations ACRS's17,18 have been designed and con­structed which will execute commands found on a com­puter generated control tape. The purpose of this report is to describe the ACRS, to discuss the use of computers to generate the paper control tape, and to demonstrate the use of a computer generated command tape in conjunction with the ACRS to synthesize a model polypeptide.

I. PRINCIPLES OF OPERATION

The ACRS was designed and constructed to carry out the physical operations normally involved in the chemical synthesis of polypeptides. These operations usually involve measuring and adding chemicals to the reaction vessel, stirring the reaction mixture, filtering, timing the sequence of additions, indicating the current status of the synthesis

331

through suitable counting means, and, in general, con­trolling the timing of all operations over a long period (weeks of operation). In the case of polypeptide synthesis, solutions of the 20 protected amino acids, a number of wash reagents, deblocking reagents, activating chemicals, neutralizing reagents, etc. must be stored and, further­more, they must be available for addition to the reaction vessel at a prescribed time and in a predetermined amount.

The sequence of events involved in the synthesis of a polypeptide by the computer oriented automated approach is illustrated in Fig. 1. In this approach the investigator specifies the desired amino acid sequence by suitable means. The command tape for the complete synthesis of the polypeptide or protein is then generated by computers using appropriate computer programs (see Sec. IV). The command tape is introduced into the tape reader of the ACRS unit and is translated (by the decoder) into the corresponding physical operation. The tape moves to the next command at intervals specified by the investigator through the computer program and methodically executes the complete chemical synthesis.

II. DESCRIPTION OF THE AUTOMATIC CHEMICAL REACTION SYSTEM

The ACRS is shown in Fig. 2 (block diagram is provided in Fig. 3). The commands for the physical operations in a chemical synthesis are punched (by a computer) onto a paper command tape (3). The command tape is read by the tape reader (2). The holes are punched into the tape in binary form and the pilot lights (9) indicate the binary code on the tape being read at a given time. Pilot lights were lit at positions 3 and 6 at the time the photograph (Fig. 2) was taken indicating a corresponding hole at positions 3 and 6 on the tape. The holes are translated through a decoder consisting of relay trees through which the electronic pulses are channeled to the appropriate site of action. A number of different relay trees have been in­vestigated. In one case, the eight positions on the tape

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332 TOMETSKO, GARDEN, II, AND TISCHlO

FIG. L The sequence of events il!volved in t~e computer o~iente~ approach to the automated chemical synthesIs of polypeptldes IS illustrated.

were divided into two sets of hole combinations. Set I in­volved the first five positions on the tape and gave a possi­bility of 31 different operations. The remaining three tape positions permitted an additional seven operations. By dividing the tape code in this manner, it is possible to execute two operations simultaneously. For example, a stirring operation could be terminated after a time interval (e.g., 30 sec) by using an appropriate combination of holes (set I) to activate the stirring circuit and another combi­nation (set II) to activate the necessary time delay circuit. In other cases it could be desirable to stir one chemical while another is being added. Combinations of holes in the two code sets make such dual operations possible. The decoder translates each position on the tape.

If a protected amino acid is to be added to the reaction vessel, the decoder sends a pulse to the prescribed solenoid operated valve (three way, normally closed) and the solenoid valve in turn controls the flow of nitrogen gas to the appropriate chemical container and dispenses the

FIG. 2. A photograph of an automatic chem­ical reaction system. The following compo­nents are shown. l­On-off switch; 2-tape reader; 3-paper com­mand tape; 4-reac­tion vessel; 5-pulse generating timer; 6-continuous movement tape advance switch; 7 - single movement (one command) tape advance switch; 8-timer reset switch; 9-pilot lights correspond­ing to tape and switches for manual operation; lO-man­ual-automatic mode switch; ll-pilot lights showing operation be­ing executed; 12-counter; 13-stirrer control; 14-stirrer shaft.

FIG. 3. A block diagram of the automatic chemical reaction system.

solution. Pilot lights (11) indicate which solution is being added.

The volumes of solution have been measured either photoelectrically or through measuring vessels. A typical photoelectric measuring vessel is shown in Fig. 4. "Cpon addition of a solution to the measuring vessel, the vessel (1) and side arm (3) fill, causing a corresponding rise in a silicone-iodine solution (4) contained in the U part of the side arm. As the dark iodine solution breaks the light beam (between 6 and 7), further addition stops, and the contents of the measuring vessel empty into the reaction vessel by activating the solenoid valve (8) which in turn opens valve 9. The intensity of light bulbs will usually decrease with time. The use of the dark silicone-iodine solution permits use of a higher initial intensity. The higher initial intensity lowers the possibility that the light intensity will diminish below the photocell triggering level during a synthesis.

A second type of measuring vessel that has been used is shown in Fig. S. In this case, a three port measuring vessel is positioned at the bottom of the storage container. This vessel contains a glass check valve (4) at one entrance

FIG. 4. A photoelec­tric measuring vessel used in the ACRS. I-Measuring cham­ber; 2-solution (cross hatched) ; 3-side arm; 4-silicone-iodine so­lution; 5-upper part of side arm with pro­tective cap; 6-photo­cell; 7-light source; 8 -solenoid; 9-ground glass valve with metal core.

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AUTOMATED CHEMICAL SYNTHESIS 333

port through which the vessel is filled with the stored solution (2). The two other ports are used to dispense the contents of the reaction vessel. In the dispensing operation, nitrogen pressure is placed on the measuring vessel by opening a three way normally closed valve (7) which is connected to port (5) and the contents are displaced through port (6) to the reaction vessel. Since the check valve (4) is closed by the nitrogen pressure within the vessel when valve 7 is open, additional solution is pre­vented from entering the measuring vessel during the dispensing process. Upon release of the nitrogen pressure, the vessel refills and is ready for the next chemical addi­tion. This approach saves measuring time since each solu­tion is premeasured and held in reserve for instantaneous delivery.

The reaction vessel contains a coarse sintered glass bottom for filtration operations and is routinely filtered by applying a vacuum to the exit line. The corrosiveness of the chemicals has prevented the use of regular valves in the vacuum system. H0wever, Tefton-glass valves have been used with success. The corrosive problem was also overcome by placing a solenoid valve on a water line and connecting a water aspirator to the valve. When the valve opens, the water running through the aspirator places a vacuum on the exit line of reaction vessel and causes the contents to be filtered. A siphon section at the bottom of the reaction vessel or positive nitrogen pressure below the sintered glass plate prevents the loss of solution prior to evacuation.

The movement of the command tape (3, Fig. 2) is con­trolled by a pulse generating timer (5), which is the primary control of the tape advance. The timer could be readily set at any desired time interval between pulses (movement of the tape) and it is usually set for a specified time interval for a given synthesis. In cases where shorter time intervals are desirable, a number of time delay circuits are available which can be coded in set II (last three holes) on the tape. The computer will introduce the appropriate time delay code by either specifying it in the main com­puter program or introducing it as a variable in the com­puter data set. When a time delay circuit is activated, a pulse is sent to the tape reader which moves the tape to the next position and thus terminates the current reading. Time delays of 10, 30 and 60 sec are being used routinely in our ACRS units.

The importance of saving time becomes more obvious during a lengthy synthesis. Thus, if 1 min were saved during each coupling cycle in synthesizing a 120 amino acid protein, the saving of 2 h would be realized by the end of the synthesis. Actually there are many points (e.g., each wash cycle) where time saving could be made. An assortment of time delays permits most efficient use of time.

In order to permit flexibility in making changes in the

FIG. 5. A gravity TO REACTION VESSEl filling measuring vessel within a solution reser­voir. 1-Stock solution bottle; 2-stock so­lution; 3-measuring vessel; 4-check valve through which (3) is filled; 5-entrance port from nitrogen tank; 6 -exit port for solution (3); 7-three way nor­mally closed valve (controls flow of N 2) ; 8-arrows indicate movement of gas at (5) and solution at (4) and (6).

FROM NITROGEN TANK

synthetic approach after the tape has been generated, a manual-automatic mode switch was incorporated into the system. Thus, if switch 10 is pressed down, the unit is in the manual mode (the tape is not being read) and the operations are executed manually by pressing the switches (9) to execute the desired function (e.g., adding a chemical, stirring, etc.). Once the necessary corrections have been implemented the tape could be advanced by pressing button 6 for continuous movement of the tape or by pressing button 7 to move the tape to the next command. If the command tape is in the proper position, the ARCS could be returned to the automatic mode by resetting switch 10 and the synthesis continues automatically again following the control tape. The manual mode has proved to be particularly useful in up-dating (making minor variations) in a previously used control tape and is im­portant for efficient use of the ACRS.

A counter has been incorporated into the hardware in order to show the current status of a synthesis. The com­puter program is written to generate a command to increment the counter (12) by one unit at the beginning of each synthetic cycle. This type of record of the progress of the chemical operations is particularly useful during the synthesis of long polypeptide sequences (e.g., 100 amino acids). Thus, if the counter registered the number 49, the investigator would immediately know that the ACRS unit was executing the addition of the 49th amino acid at the present positions on the command tape.

III. FORMAT OF THE CONTROL TAPE

The ACRS is designed to translate an eight channel control tape. The control tape is read with a binary coded decimal (BCD) format, which provides 2n-l commands, where n is the number of holes in the set. Thus, set I in­cludes five channels on the tape (n=5) and provides 31 commands, whereas set II includes three channels (n =3) and provides seven commands. The hole patterns (H) along with the corresponding decimal equivalents (D) and the operational functions for each combination are listed

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334 TOMETSKO, GARDEN, II, AND TISCHIO

TABLE I. The hole patterns (H), the decimal equivalent (D), and the corresponding function for sets I and II.

Holes Decimal (H) (D) Function

Set I 1 1 Add Gly 2 2 Add Ala 1,2 3 Add Ser 3 4 Add Pro 3,1 5 Add Val 3,2 6 Add Thr 3,2,1 7 Add Ile 4 8 Add Leu 4,1 9 Add Asn 4, 2 10 Add Asp 4,2,1 11 Add Gln 4,3 12 Add Glu 4,3,1 13 Add Met 4,3,2 14 Add His 4,3,2,1 15 Add Phe 5 16 Add Tyr 5,1 17 Add Trp 5,2 18 Add Arg 5, 2, 1 19 Add Cys 5,3 20 Add Lys 5,3,1 21 Deblock 5,3,2 22 Activation 5,3,2, 1 23 Filtration 5, 4 24 Count 5,4,1 25 Off 5,4,2 26 Time delay 5,4,2, 1 27 Add CHCla 5,4,3 28 Add ETOH 5,4,3,1 29 Add ETaN 5,4,3,!2 30 Unassigned 5,4,3,12,1 31 Unassigned

Set II 6 32 Stir 7 64 Time delay 7,6 96 Unassigned 8 128 Time delay 8, 6 160 Unassigned 8,7 192 Unassigned 8,7,6 224 Unassigned

in Table I. If the amino acid, valine, is to be added to the reaction vessel, the BCD equivalent of the decimal, 5 (D=5), would appear on the tape (Le., holes in positions 1 and 3 (H 1 and H 3). The set II codes are incorporated in to the command tape by adding the decimal equivalent in set II to the decimal equivalent in set I. For example, a stirring command would be represented by the decimal equivalent 32 on the control tape. (Note that 32 is the first channel in set II.) If a chemical is to be added [e.g., activating agent (D=22)] and the resulting mixture is to be stirred during the addition, the code on the tape would be the BCD equivalent of the sum of 22 and 32. Thus,

tape code=D(I)+D(I1)=22+32 and

tape code = (H 6,H 4,H 2) & H 6.

In decoding the command tape, the occurrence of a hole fires the coil of the corresponding relay in the appropriate relay tree.

IV. GENERATING CONTROL TAPES BY COMPUTER

In addition to the development of the hardware (ACRS), research has been directed to a method for generating the necessary software (i.e., the paper command tape). A control tape for the synthesis of a protein could contain thousands of operational commands. Therefore, a method was needed which would generate large numbers of commands (e.g., 40000) with speed and reliability. Since the series of physical operations involved in any synthesis takes place sequentially with time, and the series is essentially analogous to a one-dimensional array, a com­puter appeared to be the obvious candidate for generating the paper control tapes. The computer approach offered

OIMENSiON ISEac 10000). JPEP(200) C)IMENSION AWSH( .,.SIIISHe.) .eWSHC. J .OW!;Mf4' .ETN( I

1 FORMAT C 17 J 10 FQRMAT(4X.17)

900 FORiMAT (1"11 ISO jt"ORMATC811'1

INTEGER ACT.ST IR,F IL T.WASH.QEBL.OFF INTEGER AWSH.BWSH.CWSH.OWSM.ETN TEME"'I.!!; IM_80 IN_2° l"'IN-25 DEeL a 21 ACT-22 ITI -,28 IT2-6. FILTa23 CNT-Z4 011',..-25 STI,q-32 REAQC5. III AIilSHIHI .Hat .31 REAO 15.t, I BWSHIHI .Hal. 3, READI~.t' CCIIISHCH) .Hat • .)1 REAOI~. 1 I IDWSHCHI .Hat .3, REAO(~. t I (ETHCH, .Hal.e, REAO(5",CtPEJ)CHI. Nal.tMINI

""0 00 200 N-t.IJiIIIIN JaJ+l ISEOIJlaCHT ..1-.)+1 ISEOI J)_IPEPIN,+I Tl ..1_.)+1 ISI!OCJ,-STtR J-J+I ISI!OCJI_ACT+ITI 005'51-1.1'" .)-.)+' I~QCJlaST,R

~5 CONT I NIJE J_.)+t ISEQIJ) -PIL T+i T2 00 61 '-1.3 0060 "-"3 .)_..1+1 12QIJ'aAWSHf",

60 CONTINJ!

61 CONTINUE DO 65 1."3 00 6. "a"3 ..1_.)+' J201.))-eWSHCK)

6. CONTINJE: 65 CC)NTINJE

00 71 (-1.3 00..,0 K-t.3 J-J+' IHQCJ,-.,WSHCIC'

70 CONTINJE 71 CONTINU!

..1-..1.1 . ISEQI')'-0ES.·1TI DO eo I_,.IH ..1_..1.' IS!QIJI-STlf:I

eo CONTINUE ..1_.)+1 ISEQc.)I· ... ILT+IT2 00 91 1(-1-3 0090 1-1.3 ..1_..1"'. ISEOIJI·AWSHf II

90 CONTINJE 91 CONTINUE:

00 liD 1_1,8 .)-..1+1: IS!:QCI.),aETNIII

110 CONTIiNve: DOtt!6k.I.3 00 1'5 t_l.3

'"""+1 ISEQ_JlaAWSHC I)

liS CONTCNIJe: 116 COHTtNJI:

zoo CONTI''''''' ..1-..1. ISEQ J'aOP'''' WRIT 16,,50,.) "'IT C6.150'(ISEQC I) •• _1.5001 WR I Tit 16.9001 C 1P!P'fN' .N_t .1MINI

:::~~ ~:: ::~: :t~~;! ;~! 1_1,..1' STOP!IZ3 ENO

FIG. 6. A reproduc­tion of the FORTRAN IV computer program . This program sets up an array of decimal commands and stores them on magnetic tape.

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AUTOMATED CHEMICAL SYNTHESIS 335

an additional advantage of making possible variations in the synthesis procedure which could be tailored for each amino acid with no significant loss of time in preparing the tape. Once the basic programs were developed, the variables could be added as the information concerning specific reaction conditions for each amino acid became available. Thus, operationally, the computer (through the programs) not only generates an array of commands for carrying out the physical operations of synthesis, but also sets up the timing of each operation by synchronizing the movement of the control tape (i.e., the flow of com­mands) with the primary pulse generating timer. The computer also controls the duration of operations by adding appropriate time delay codes to the command array where they were needed. The computer approaches to generating the control tape have been developed using either FORTRAN IV programs (Fig. 6) (for use with an IBM-360-44 computer) or symbolic assembler language programsl9 (PDP-7 computer).

Using the FORTRAN IV programs (Fig. 6), physical opera­tions involved in the chemical synthesis are incorporated into the main program, along with necessary variables. Wash cycles (AWSH, BWSH, CWSH, ETN) are read into the' computer with the data section of the program and are called upon as required. The amino acid sequence is submitted on data cards. One card is submitted for each amino acid in the desired sequence. Thus, if the sequence Leu.Leu.Thr.Phe. was to be synthesized, four data cards (IMIN =4) corresponding to Leu, Leu, Thr, and Phe would be placed at the end of the data section of the program and would be read into the computer along with the program and other data. If a 200 amino acid sequence was to be synthesized, 200 data cards in the appropriate sequence would be submitted. The computer through the program then sets up a one-dimensional array of commands for the complete synthesis of the polypeptide or protein. The array is then transferred to a magnetic tape. The magnetic tape is translated20 using a PDP-7 computer (equipped with a Dec-tape terminal) into a BCD paper tape output which parallels the decimal commands found on the magnetic tape. By this method, the paper tape is

TABLE II. Molar ratios· of amino acids after each deblocking step for the synthesis of H.Leu.Gly.Ala.Leu.Gly.Ala.OH.

Deblocking step Ala. Gly. Leu.

1 1.00 0 0 2 1.00 1.16 0 3 1.00 1.18 1.22 4 2.00 1.00 0.85 5 2.00 2.30 1.00 6 2.00 2.31 2.20

• The molar ratios of alanine obtained upon amino acid analysis of the polypeptide were taken as 1.00 or 2.00.

prepared with speed (60 commands/second) and with reliabili ty.

The symbolic assembler language approach makes use of the PDP-7 computer directly. The assembler language programl9 is read into the computer. The numerical code for each amino acid is then typed into the computer through a Teletype terminal. The computer then generates the command tape for the total synthesis. Either approach results in the production of a paper command tape for the total synthesis of a polypeptide in a few minutes.

V. SYNTHESIS OF A MODEL POLYPEPTIDE WITH THE ACRS AND A COMPUTER GENERATED CONTROL TAPE

The computer program (see previous section) is de­signed to generate commands for carrying out the total synthesis of a polypeptide once the amino acid sequence has been specified. In this study, the desired sequence, L-Ieucylglycyl-L-alanyl-L-leucylglycyl-L-alanine, was used to generate the control tape by placing five cards corre­sponding to leu, gly, ala, leu, and gly, respectively, in the data section of the program (FORTRAN IV program) or typing in the amino acid sequence (assembler language program). The C-terminal alanine (sixth amino acid) initially was attached to the resin by the method of Merri­field" and was deblocked by treatment with 50% TFA in CHCla for 30 min. Stock solutions of 0.2M t-butoxy­carbonyl amino acids (leucine, alanine, and glycine) in CHCla were placed in the ACRS unit along with (1) the activating agent [0.2M dicyclohexycarbodiimide (DCC) in CHCla], (2) chloroform, (3) 50% TFA in CHCla, (4) 10% ETaN in chloroform, and (5) ethanol. The L-alanine resin was placed in the reaction vessel and the paper command tape was then fed into the ACRS unit and the synthesis commenced. The resin was washed with CHCla three times and t-butoxycarbonyl glycine (30 ml) was added. The reSUlting mixture was stirred for 1 min and 0.3M DCC solution (30 ml) was added. After stirring at room temperature for 2 h the mixture was filtered and was washed three times each with chloroform, ethanol, and chloroform, and the deblocking reagent (50% TFA in CHCh) (60 ml) was added. After stirring at room tempera­ture for 30 min, the mixture was filtered, washed three times with CHCla, and 10% ETaN in CHCla (60 ml) was added. The neutralized resin was filtered after stirring for 10 min and was washed three times with chloroform (60 ml each). The resin was then ready for the next amino acid addition. The cycle of chemical events was repeated for each amino acid in the sequence. The amino acid analysis of an acid hydrolysate of the resin following each de­blocking cycle is shown in Table II. The favorable results obtained in this study will be extended in order to deter­mine optimum reaction conditions for each coupling step . A suitable means for monitoring the current status of the

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336 TOMETSKO, GARDEN, II, AND TISCHIO

synthesis should be developed in subsequent research in order to provide feedback to the computer programs on specific conditions for reacting each amino acid.

VI. RESULTS

Generally, synthetic problems might be represented by a series of operations taking place over a period of time. Each operation must take place at a prescribed time and each will require a period of time for completion. This type of time distribution is applicable to most synthetic methods where different operations (e.g., extractions, fil­trations, chemical additions, etc.) are involved. In order to make more efficient use of time during chemical syn­thesis and to focus on the chemistry of the synthesis rather than on the physical operations, an ACRS unit (Fig. 2) has been constructed which will carry out the physical operations involved in chemical synthesis. The ACRS approach has an important difference from classical approaches. Decision making is for all practical purposes eliminated once the synthesis has begun, since the ACRS will follow the commands precisely as found on the tape. Therefore, the chemical events for the total synthesis must be reviewed and evaluated before the synthesis is undertaken.

It should be pointed out that the computer generated programs provide a tool more powerful than is realized in the synthesis of the model peptide described in this report. For example, the computer could select reaction conditions (e.g., reaction time, amounts of reagents, wash cycles, etc.) that would be tailored for each individual amino acid in essentially the same time taken to generate these simple tape programs. This programming flexibility is important since each synthesis presents different and often unique problems.

Automatic chemical reaction system has recently been applied to the solid phase Edman degradation of poly-

peptides.2l Future development could find this approach useful in other areas of chemistry with some modification of the basic hardware (ACRS) and software (computer programs).

ACKNOWLEDGMENTS

The authors wish to express their appreciation to George Mourtzikos for the amino acid analysis and to Ruth Howard for computing assistance.

* The Development of the automatic chemical reaction system was supported by the Chemtrox Corporation, Rochester, N. Y.

1 P. G. Katsoyannis, A. M. Tometsko, and K. Fukuda, J. Amer. Chern. Soc. 85, 2863 (1963).

2 P. G. Katsoyannis, K. Fukuda, A. M. Tometsko, K. Suzuki, and M. TiIak, J. Amer. Chern. Soc. 86, 930 (1964).

3 P. G. Katsoyannis, A. M. Tometsko, C. Zalut, and K. Fukuda, J. Amer. Chern. Soc. 88, 5625 (1966).

'P. G. Katsoyannis, A. M. Tometsko, and C. Zalut, J. Amer. Chern. Soc. 89, 4565 (1967).

6 R B. Merrifield, J. Amer. Chern. Soc. 85, 2149 (1963). 6 R. B. Merrifield, Science 150, 178 (1965). 7 D. A. Ontjes and C. B. Anfinsen, J. Bio!. Chern. 244, 6316 (1969). 8 D. A. Ontjes and C. B. Anfinsen, Proc. Nat. Acad. Sci. 64, 428

(1969). 9 B. Gutte and R. B. Merrifield, J. Amer. Chern. Soc. 91, 501 (1969). 10 R. B. Merrifield, Advan. Enzymol. 32, 221 (1969). 11 J. M. Stewart and J. D. Young, Solid Phase Peptide Synthesis

(Freeman, San Francisco, 1969). 12 R. B. Merrifield, J. M. Stewart, and N. Jernberg, Anal. Chern. 38,

1905 (1966). ]A K. Brunfeldt, J. Halstrom, and P. Roepstorff, in Peptides,

edited by E. Bricas (Wiley, New York, 1968), p. 197. 14 A. Loffet and J. Close, in Ref. 13, p. 189. 16 G. W. H. A. Mansveld, H. Hindriks, and H. C. Beyerman, in

Ref. 13, p. 197. 16 K. Brunfeldt, J. Halstrom, and P. Roepstorff, Acta Chem.

Scand. 23, 2830 (1969). 17 Abbreviations: ACRS; automatic chemical reaction system;

CHela, chloroform; DCC, dicyclohexylcarbodiimide; EtaN, triethyl­amine; TFA, trifluoracetic acid; I-BOC, t-butoxycarbonyl; DMF, dimethylformamide.

18 A. M. Tometsko, patent pending. 19 A listing of the computer programs is available from the authors. 20 Program for decimal to BCD conversion was obtained from the

Atomic Energy Project (U. of R) PDP-7 program library. 21 A. M. Tometsko, J. Tischio, and J. Garden, J. Pharm. Sci.

59, 1655 (1970).

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