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            <secFileNumber>001-37708</secFileNumber>
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                <ns2:city>Waltham ,</ns2:city>
                <ns2:stateOrCountry>MA</ns2:stateOrCountry>
                <ns2:zipCode>02451</ns2:zipCode>
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            <issuerContactPhone>7814191400</issuerContactPhone>
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            <relationshipsToIssuer>
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                <address>
                    <ns2:street1>1 New York Plaza</ns2:street1>
                    <ns2:street2>38th Fl.</ns2:street2>
                    <ns2:city>New York</ns2:city>
                    <ns2:stateOrCountry>NY</ns2:stateOrCountry>
                    <ns2:zipCode>10004</ns2:zipCode>
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            <aggregateMarketValue>1072427.95</aggregateMarketValue>
            <noOfUnitsOutstanding>68821277</noOfUnitsOutstanding>
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            <securitiesExchangeName>NASDAQ</securitiesExchangeName>
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            <acquiredDate>05/09/2023</acquiredDate>
            <natureOfAcquisitionTransaction>Exercise of Stock Options</natureOfAcquisitionTransaction>
            <nameOfPersonfromWhomAcquired>Issuer</nameOfPersonfromWhomAcquired>
            <isGiftTransaction>N</isGiftTransaction>
            <amountOfSecuritiesAcquired>52855</amountOfSecuritiesAcquired>
            <paymentDate>05/09/2023</paymentDate>
            <natureOfPayment>Cash</natureOfPayment>
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                    <ns2:stateOrCountry>MA</ns2:stateOrCountry>
                    <ns2:zipCode>02451</ns2:zipCode>
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            <securitiesClassTitle>Common</securitiesClassTitle>
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            <grossProceeds>1032237.01</grossProceeds>
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                    <ns2:zipCode>02451</ns2:zipCode>
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            <grossProceeds>1190673.77</grossProceeds>
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        <noticeSignature>
            <noticeDate>05/09/2023</noticeDate>
            <planAdoptionDates>
                <planAdoptionDate>02/09/2023</planAdoptionDate>
            </planAdoptionDates>
            <signature>/s/ Briggs Morrison </signature>
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144
0001654430
XXXXXXXX
LIVE
0001395937
SYNDAX PHARMACEUTICALS INC
001-37708
35 Gatehouse Drive, Building D, Floor 3
Waltham ,
MA
02451
7814191400
BRIGGS W MORRISON &ANGELA HOOVER MORRISON JT TEN
Officer
COMMON
Morgan Stanley Smith Barney LLC Executive Financial Services
1 New York Plaza
38th Fl.
New York
NY
10004
52855
1072427.95
68821277
05/09/2023
NASDAQ
Common
05/09/2023
Exercise of Stock Options
Issuer
N
52855
05/09/2023
Cash
N
10b5-1 Sales Plan for BRIGGS W MORRISON
35 Gatehouse Drive, Building D, Floor 3
Waltham ,
MA
02451
Common
04/10/2023
52855
1032237.01
10b5-1 Sales Plan for BRIGGS W MORRISON
35 Gatehouse Drive, Building D, Floor 3
Waltham ,
MA
02451
Common
03/13/2023
52854
1190673.77
05/09/2023
02/09/2023
/s/ Briggs Morrison