X0306 4 2013-05-20 0 0001131543 AMBIT BIOSCIENCES CORP AMBI 0001055951 ORBIMED ADVISORS LLC 601 LEXINGTON AVENUE, 54TH FLOOR NEW YORK NY 10022 0 0 1 0 0001432241 OrbiMed Capital GP III LLC 601 LEXINGTON AVENUE, 54TH FLOOR NEW YORK NY 10022 0 0 1 0 0001055949 ISALY SAMUEL D 601 LEXINGTON AVENUE, 54TH FLOOR NEW YORK NY 10022 0 0 1 0 Common Stock, $0.001 par value per share 2013-05-20 4 P 0 10500 6.7773 A 10807 I See Footnotes Common Stock, $0.001 par value per share 2013-05-20 4 P 0 100 6.7773 A 102 I See Footnotes Common Stock, $0.001 par value per share 2013-05-21 4 C 0 367315 A 378122 I See Footnotes Common Stock, $0.001 par value per share 2013-05-21 4 C 0 3498 A 3600 I See Footnotes Common Stock, $0.001 par value per share 2013-05-21 4 C 0 219863 A 597985 I See Footnotes Common Stock, $0.001 par value per share 2013-05-21 4 C 0 2094 A 5694 I See Footnotes Common Stock, $0.001 par value per share 2013-05-21 4 C 0 181689 A 779674 I See Footnotes Common Stock, $0.001 par value per share 2013-05-21 4 C 0 1730 A 7424 I See Footnotes Common Stock, $0.001 par value per share 2013-05-21 4 P 0 593618 8.00 A 1373292 I See Footnotes Common Stock, $0.001 par value per share 2013-05-21 4 P 0 5653 8.00 A 13077 I See Footnotes Common Stock, $0.001 par value per share 2013-05-21 4 P 0 61910 8.00 A 1435202 I See Footnotes Common Stock, $0.001 par value per share 2013-05-21 4 P 0 590 8.00 A 13667 I See Footnotes Common Stock, $0.001 par value per share 2013-05-21 4 P 0 8020 6.8970 A 1443222 I See Footnotes Common Stock, $0.001 par value per share 2013-05-21 4 P 0 80 6.8970 A 13747 I See Footnotes Series E Convertible Preferred Stock 2013-05-21 4 C 0 8815565 D Common Stock 367315 0 I See Footnotes Series E Convertible Preferred Stock 2013-05-21 4 C 0 83959 D Common Stock 3498 0 I See Footnotes Series D-2 Convertible Preferred Stock 2013-05-21 4 C 0 5276702 D Common Stock 219863 0 I See Footnotes Series D-2 Convertible Preferred Stock 2013-05-21 4 C 0 50256 D Common Stock 2094 0 I See Footnotes Series D Convertible Preferred Stock 2013-05-21 4 C 0 1973439 D Common Stock 181689 0 I See Footnotes Series D Convertible Preferred Stock 2013-05-21 4 C 0 18795 D Common Stock 1730 0 I See Footnotes The shares were purchased by OrbiMed Private Investments III, LP ("OPI") in multiple transactions and the price reported in Column 4 is a weighted average price. These were purchased at prices ranging from $6.69 to $6.86, inclusive. Upon request, the Reporting Persons undertake to provide the Issuer, any security holder of the Issuer, or the Securities and Exchange Commission, full information regarding the shares purchased at each separate price within the ranges set forth in footnote (1) of this Form 4. The shares were purchased by OrbiMed Associates III, LP ("Associates") in multiple transactions and the price reported in Column 4 is a weighted average price. These were purchased at prices ranging from $6.69 to $6.86, inclusive. Upon request, the Reporting Persons undertake to provide the Issuer, any security holder of the Issuer, or the Securities and Exchange Commission, full information regarding the shares purchased at each separate price within the ranges set forth in footnote (2) of this Form 4. Represents shares of Common Stock acquired upon the automatic conversion of Series E convertible preferred stock upon the closing of the Issuer's initial public offering of Common Stock. The Series E convertible preferred stock did not have an expiration date. The Series E convertible preferred stock automatically converted into shares of Common Stock immediately upon the closing of the Issuer's initial public offering of Common Stock, at a conversion ratio of 1 share of Common Stock for every 24 shares of Series E convertible preferred stock, for no additional consideration. Represents shares of Common Stock acquired upon the automatic conversion of Series D-2 convertible preferred stock upon the closing of the Issuer's initial public offering of Common Stock. The Series D-2 convertible preferred stock did not have an expiration date. The Series D-2 convertible preferred stock automatically converted into shares of Common Stock immediately upon the closing of the Issuer's initial public offering of Common Stock, at a conversion ratio of 1 share of Common Stock for every 24 shares of Series D-2 convertible preferred stock, for no additional consideration. Represents shares of Common Stock acquired upon the automatic conversion of Series D convertible preferred stock upon the closing of the Issuer's initial public offering of Common Stock. The Series D convertible preferred stock did not have an expiration date. The Series D convertible preferred stock automatically converted into shares of Common Stock immediately upon the closing of the Issuer's initial public offering of Common Stock, at a conversion ratio of 1 share of Common Stock for every 10.86166 shares of Series D convertible preferred stock, for no additional consideration. These securities are held of record by OPI and may be deemed to be indirectly beneficially owned by OrbiMed Capital GP III LLC ("Capital"), OrbiMed Advisors LLC ("Advisors") and Samuel D. Isaly ("Isaly"). Capital is the sole general partner of OPI. Advisors, a registered adviser under the Investment Advisers Act of 1940, as amended, is the sole managing member of Capital. By virtue of such relationships, Capital and Advisors may be deemed to have voting and investment power with respect to the securities held by OPI noted above. Isaly, a natural person, may also be deemed to have voting and investment power with respect to the securities held by OPI noted above in his capacity as the managing member of, and holder of a controlling interest, in Advisors. As a result, each of Capital, Advisors and Isaly may be deemed to have beneficial ownership of the securities held by OPI. These securities are held of record by Associates and may be deemed to be indirectly beneficially owned by Advisors and Isaly. Advisors is the sole general partner of Associates. Isaly is the managing member of, and holder of a controlling interest in, Advisors. By virtue of such relationship, Advisors and Isaly may be deemed to have voting and investment power with respect to the securities held by Associates noted above. As a result, each of Advisors and Isaly may be deemed to have beneficial ownership of the securities held by Associates. This report on Form 4 is jointly filed by Capital, Advisors and Isaly. Each of the Reporting Persons disclaims beneficial ownership of the securities reported herein for purposes of Rule 16a-1(a) under the Securities Exchange Act of 1934, as amended (the "Exchange Act"), except to the extent of its or his pecuniary interest therein, if any. The Reporting Persons have designated a representative, currently David P. Bonita, an employee of Advisors, to serve on the Issuer's board of directors. This report shall not be deemed an admission that the Reporting Persons are beneficial owners for the purpose of Section 16 of the Exchange Act, or for any other purpose. The shares were purchased by OPI in a private placement concurrent with the closing of the Issuer's initial public offering. The shares were purchased by Associates in a private placement concurrent with the closing of the Issuer's initial public offering. The shares were purchased by OPI at the Issuer's initial public offering. The shares were purchased by Associates at the Issuer's initial public offering. The shares were purchased by OPI in multiple transactions and the price reported in Column 4 is a weighted average price. These were purchased at prices ranging from $6.77 to $7.00, inclusive. Upon request, the Reporting Persons undertake to provide the Issuer, any security holder of the Issuer, or the Securities and Exchange Commission, full information regarding the shares purchased at each separate price within the ranges set forth in footnote (14) of this Form 4. The shares were purchased by Associates in multiple transactions and the price reported in Column 4 is a weighted average price. These were purchased at prices ranging from $6.77 to $7.00, inclusive. Upon request, the Reporting Persons undertake to provide the Issuer, any security holder of the Issuer, or the Securities and Exchange Commission, full information regarding the shares purchased at each separate price within the ranges set forth in footnote (15) of this Form 4. /s/ Samuel D. Isaly 2013-05-22