FORM 4
Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).
UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP OF SECURITIES

Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934 or Section 30(h) of the Investment Company Act of 1940
OMB APPROVAL
OMB Number: 3235-0287
Estimated average burden hours per response... 0.5

(Print or Type Responses)
1. Name and Address of Reporting Person *
KIRK RANDAL J
  2. Issuer Name and Ticker or Trading Symbol
Synthetic Biologics, Inc. [SYN]
5. Relationship of Reporting Person(s) to Issuer
(Check all applicable)
_____ Director __X__ 10% Owner
_____ Officer (give title below) _____ Other (specify below)
(Last)
(First)
(Middle)
C/O THIRD SECURITY, LLC, 1881 GROVE AVENUE
3. Date of Earliest Transaction (Month/Day/Year)
04/01/2019
(Street)

RADFORD, VA 24141
4. If Amendment, Date Original Filed(Month/Day/Year)
6. Individual or Joint/Group Filing(Check Applicable Line)
___ Form filed by One Reporting Person
_X_ Form filed by More than One Reporting Person
(City)
(State)
(Zip)
Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1.Title of Security
(Instr. 3)
2. Transaction Date (Month/Day/Year) 2A. Deemed Execution Date, if any (Month/Day/Year) 3. Transaction Code
(Instr. 8)
4. Securities Acquired (A) or Disposed of (D)
(Instr. 3, 4 and 5)
5. Amount of Securities Beneficially Owned Following Reported Transaction(s)
(Instr. 3 and 4)
6. Ownership Form: Direct (D) or Indirect (I)
(Instr. 4)
7. Nature of Indirect Beneficial Ownership
(Instr. 4)
Code V Amount (A) or (D) Price
Common Stock 04/01/2019   S   11,413 (1) D $ 0.67 (1) 92,159 (2) I by NRM VII Holdings (3)
Common Stock 04/01/2019   S   30,265 (1) D $ 0.67 (1) 244,402 (2) I by Intrexon (4)
Common Stock 04/02/2019   S   3,737 (1) D $ 0.66 (1) 88,422 (2) I by NRM VII Holdings (3)
Common Stock 04/02/2019   S   9,909 (1) D $ 0.66 (1) 234,493 (2) I by Intrexon (4)
Common Stock 04/03/2019   S   26,080 (1) D $ 0.65 (1) 62,342 (2) I by NRM VII Holdings (3)
Common Stock 04/03/2019   S   69,161 (1) D $ 0.65 (1) 165,332 (2) I by Intrexon (4)

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB control number. SEC 1474 (9-02)

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned
(e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security
(Instr. 3)
2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (Month/Day/Year) 3A. Deemed Execution Date, if any (Month/Day/Year) 4. Transaction Code
(Instr. 8)
5. Number of Derivative Securities Acquired (A) or Disposed of (D)
(Instr. 3, 4, and 5)
6. Date Exercisable and Expiration Date
(Month/Day/Year)
7. Title and Amount of Underlying Securities
(Instr. 3 and 4)
8. Price of Derivative Security
(Instr. 5)
9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s)
(Instr. 4)
10. Ownership Form of Derivative Security: Direct (D) or Indirect (I)
(Instr. 4)
11. Nature of Indirect Beneficial Ownership
(Instr. 4)
Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares

Reporting Owners

Reporting Owner Name / Address Relationships
 Director  10% Owner  Officer  Other
KIRK RANDAL J
C/O THIRD SECURITY, LLC
1881 GROVE AVENUE
RADFORD, VA 24141
    X    
INTREXON CORP
C/O LEGAL DEPARTMENT
20374 SENECA MEADOWS PARKWAY
GERMANTOWN, MD 20876
    X    

Signatures

 /s/ Randal J. Kirk   04/03/2019
**Signature of Reporting Person Date

 /s/ Randal J. Kirk, CEO of Intrexon Corporation   04/03/2019
**Signature of Reporting Person Date

Explanation of Responses:

* If the form is filed by more than one reporting person, see Instruction 4(b)(v).
** Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
(1) Pursuant to a joint selling program, NRM VII Holdings I, LLC ("NRM VII Holdings") and Intrexon Corporation ("Intrexon") sold shares on a pro rata basis.
(2) The indicated share amount is reflective of a 1:35 reverse stock split effected by the issuer on August 10, 2018.
(3) Randal J. Kirk controls NRM VII Holdings. Shares held by this entity may be deemed to be indirectly beneficially owned (as defined under Rule 13d- 3 promulgated under the Securities Exchange Act of 1934, as amended) by Mr. Kirk. Mr. Kirk disclaims beneficial ownership of such shares, except to the extent of any pecuniary interest therein.
(4) Randal J. Kirk, directly and through certain affiliates, is the largest shareholder of Intrexon and serves as Intrexon's Chairman of the Board and Chief Executive Officer. Mr. Kirk may therefore be deemed to have voting and dispositive power over the shares of the issuer owned by Intrexon. Shares held by Intrexon may be deemed to be indirectly beneficially owned (as defined under Rule 13d-3 promulgated under the Securities Exchange Act of 1934, as amended) by Mr. Kirk. Mr. Kirk disclaims beneficial ownership of such shares, except to the extent of any pecuniary interest therein.

Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.

Potential persons who are to respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB number.