THOR Synthorx Inc

Synthorx, Inc. (Nasdaq: THOR), a biotechnology company using a first-of-its-kind Expanded Genetic Alphabet platform technology to discover and develop optimized biologics for cancer and autoimmune disorders, today announced the pricing of its initial public offering of 11,912,727 shares of common stock at a public offering price of $11.00 per share.  Synthorx anticipates total gross proceeds of approximately $131 million, before deducting underwriting discounts and commissions and other offering expenses. All shares of common stock are being offered by Synthorx. The shares are expected to begin trading on The Nasdaq Global Select Market on December 7, 2018 under the ticker symbol "THOR." The offering is expected to close on or about December 11, 2018, subject to customary closing conditions. In addition, Synthorx has granted the underwriters a 30-day option to purchase up to an additional 1,786,909 shares of common stock at the initial public offering price.

Jefferies LLC, Leerink Partners LLC and Evercore ISI are acting as joint book-running managers for the offering. H.C. Wainwright & Co., LLC is acting as lead manager for the offering.

Registration statements relating to these securities have been filed with the Securities and Exchange Commission and became effective on December 6, 2018. The offering will be made only by means of a prospectus. Copies of the final prospectus relating to the offering, when available, may be obtained from Jefferies LLC, Attention: Equity Syndicate Prospectus Department, 520 Madison Avenue, 2nd Floor, New York, NY 10022 or by telephone at (877) 547-6340 or by email at Prospectus_Department@Jefferies.com; Leerink Partners LLC, Attention: Syndicate Department, One Federal Street, 37th Floor, Boston, MA 02110 or by telephone at (800) 808-7525, ext. 6132 or by email at syndicate@leerink.com; or Evercore Group L.L.C., Attention: Equity Capital Markets, 55 East 52nd Street, New York, NY 10055 or by telephone at (888) 474-0200 or by email at ecm.prospectus@evercore.com.

This press release shall not constitute an offer to sell or the solicitation of an offer to buy, nor shall there be any sale of these securities in any state or jurisdiction in which such offer, solicitation or sale would be unlawful prior to registration or qualification under the securities laws of any such state or jurisdiction.

About Synthorx

Synthorx, Inc. is a biotechnology company focused on prolonging and improving the lives of people with cancer and autoimmune disorders. Synthorx’s proprietary, first-of-its-kind Expanded Genetic Alphabet platform technology expands the genetic code by adding a new DNA base pair and is designed to create optimized biologics, referred to as Synthorins. A Synthorin is a protein optimized through incorporation of novel amino acids encoded by the new DNA base pair that enables site-specific modifications, which enhance the pharmacological properties of these therapeutics. The company’s lead product candidate, THOR-707, a variant of IL-2, is in development in multiple tumor types as a single agent and in combination with an immune checkpoint inhibitor. The company was founded based on important discoveries in Dr. Floyd Romesberg’s lab at The Scripps Research Institute. The company is headquartered in La Jolla, Calif.

Corporate Development/IR Contact: Enoch Kariuki, Pharm.D.Synthorx, Inc.ekariuki@synthorx.com 858-750-4750

Media Relations ContactLauren FishCanale Communicationslauren@canalecomm.com619-849-5386