Document:

Employment agreement between the Registrant and Mark Leuchtenberger

 Exhibit 10.15 
 Execution Copy 
 EMPLOYMENT AGREEMENT 

THIS EMPLOYMENT AGREEMENT (hereinafter “this Agreement”) is made this 19th day of March 2010 between Rib-X Pharmaceuticals,
Inc., a Delaware corporation, (hereinafter “the Company”) and Mark Leuchtenberger an individual who resides at 20 Old Farm Road, Newton, Massachusetts 02459 (hereinafter the “Executive”). 

WHEREAS, the Company desires to employ the Executive as its President and Chief Executive Officer and the Executive desires to be so
employed by the Company, on the terms and conditions hereinafter set forth; 
 NOW, THEREFORE, in consideration of the foregoing
and of the respective covenants and agreements herein set forth, the Company and the Executive hereby agree as follows: 
 1.
Employment. The Company hereby agrees to employ the Executive, and the Executive hereby agrees to serve as the President and Chief Executive Officer of the Company. The Executive agrees to perform such services customary to that office and
other such duties and responsibilities as shall from time to time be assigned to him by the Company’s Board of Directors (the “Board”). The Executive may hire senior level executives with the Board’s approval, which approval
shall not be unreasonably withheld. The Executive further agrees to use his best efforts to promote the interests of the Company and to devote his full business time and energies to the business and affairs of the Company. The Executive may continue
to serve on the board of directors of Beth Israel Deaconess Medical Center, the Massachusetts Biotech Council and Wake Forest University, and may agree to serve on up to two (2) additional “for-profit” boards upon prior approval of
the Board, which approval will not be unreasonably withheld, provided, however, that the Executive’s participation in such activities does not unreasonably interfere (as determined in the good faith discretion of the Board), with the
performance of his duties hereunder. The Executive shall perform his full-time services at the Company’s offices in New Haven, Connecticut or as otherwise agreed with the Board; provided that, the Executive may be required to travel as
necessary to perform his duties hereunder. 
 2. Board of Directors. While the Executive remains employed with the
Company under this Agreement, the Executive shall be elected to serve as a director on the Board. In the event the Executive’s employment terminates for any reason, the Executive shall concurrently resign his appointment as a director.

 3. Term of Employment. The Executive’s employment shall commence on March 23, 2010 (the “Commencement
Date”). The Executive’s employment hereunder shall be at-will, and either the Executive or the Company may terminate the Executive’s employment at any time, with or without notice, and for any reason on thirty (30) days prior
written notice by one party to the other party. Nothing contained herein shall be deemed to constitute a promise or representation of guaranteed employment or employment for any specific period of time. 

4. Compensation and Other Related Matters. 
 (a) Salary. As compensation for services rendered hereunder, the Executive shall initially receive an annual Base Salary of $400,000, less applicable withholding, which salary shall be paid in
accordance with the Company’s then prevailing payroll practices. The Company’s Board agrees to review such salary annually and consider appropriate increases, if any, with the first such review occurring within sixty (60) days after
the end of calendar year 2010. 

 (b) Bonus. During the term of this Agreement, and in the Company’s sole
discretion, the Executive shall be eligible to receive an Annual Bonus of up to 50% of his Base Salary (subject to applicable withholdings) at the end of each calendar year based on the Executive and the Company successfully achieving targeted
annual performance objectives established by the Board. The Board shall attempt, in good faith, to establish such annual performance objectives for calendar year 2010, in writing, within the sixty (60) day period following the Commencement
Date. The Board, in its sole discretion, shall determine the extent to which the Executive has achieved the performance objectives upon with the Annual Bonus is based, and the amount of Annual Bonus to be paid to the Executive, if any. The Annual
Bonus is not earned until it is approved in writing by the Board. To receive such Annual Bonus, the Executive must still be employed with the Company as of December 31 of the year for which the Annual Bonus is payable and not be in breach of
this Agreement. The Annual Bonus shall be payable prior to March 15 of the following calendar year. The Executive shall receive a pro-rata portion of the Annual Bonus that relates to calendar year 2010 based on the actual Commencement Date.

 (c) Signing Bonus. The Company shall pay the Executive a signing bonus in an aggregate amount of $50,000, less
applicable withholding, (the “Signing Bonus”) on the Commencement Date. If the Executive terminates his employment for any reason other than Good Reason (as defined below) prior to the one-year anniversary of the Commencement Date, the
Executive shall return the Signing Bonus to the Company within ten (10) days of the date of termination. 
 (d) Equity
Incentive. 
 (i) Grant of Options. On the Commencement Date, the Company shall grant the
Executive an option to purchase 13,339,196 shares of the common stock of the Company (the “Option”), representing 4% of the equity of the Company on a fully diluted basis, pursuant to and subject to the terms and conditions in the
Company’s 2001 Stock Option and Incentive Plan (the “Plan”). The exercise price of the Option shall be the fair market value of the Company’s common stock on the Commencement Date, as determined by the Board in its reasonable,
good faith discretion. The Option shall initially be unvested and, provided the Executive remains employed by the Company on the applicable vesting date, shall vest over time as follows: (i) 25% of the Options shall vest on the first
anniversary of the Commencement date; and (ii) the remaining 75% of the Options shall vest at the rate of
1/48th of the Options per month on each monthly
anniversary of the Commencement Date such that all of the Options shall be vested fully on the fourth anniversary of the Commencement Date. All unvested Options shall immediately vest and become exercisable upon the effective date of a Change in
Control, as that term is defined in the Option Agreement. 
 (ii) Anti-Dilution. If the Company consummates an equity
financing prior to March 31, 2011 which results in aggregate proceeds to the Company of at least $20 million (the “Transaction”), the Executive’s Option will constitute less than 4% of the

  

			
	Leuchtenberger Employment Agreement	  	2

 
Company’s equity on a fully diluted, as-if exercised basis (assuming full conversion of all convertible securities, including the exchange of all exchangeable shares, and full exercise of
all outstanding warrants and options and all options reserved for issuance under the Plan) (a “Fully Diluted Basis”). Accordingly, upon the occurrence of such Transaction, the Company agrees to grant the Executive the option to purchase
additional shares of the common stock of the Company (the “Second Option”) such that the Option and the Second Option together represent 4% of the equity of the Company on a Fully Diluted Basis. The Second Option shall be granted to the
Executive pursuant to and subject to the terms and conditions of the Plan. The exercise price of the Second Option shall be the fair market value of the Company’s common stock on the date the Transaction becomes effective and shall be based on
the fair market value of the Company as determined by the Transaction. The Second Option shall initially be unvested, and provided the Executive remains employed by the Company on the applicable vesting date, shall vest on the same terms and
conditions as the Option. 
 (e) Other Benefits. The Executive shall be entitled to thirty (30) days of vacation
leave per year. Additional fringe benefits, perquisites and other benefits of employment to be provided to the Executive, including without limitation, retirement, health, life and disability insurances, shall be equivalent to such benefits and
perquisites as are provided to other senior executives of the Company as amended from time to time. If at any time the Company provides a greater level of benefits to any other senior executive of the Company, then the Executive shall be entitled to
receive such benefits. 
 (f) Expense Reimbursement. The Executive will be reimbursed for all reasonable out-of-pocket
expenses actually incurred by him in the furtherance of his duties under this Agreement. Such expenses shall be reimbursed upon submission to the Company of invoices containing original receipts for all such expenditures, and upon review by the
Company with respect to the reasonable nature thereof. If a business expense reimbursement is not exempt from Section 409A of the United States Tax Code, (i) any reimbursement in one calendar year shall not affect the amount that may be
reimbursed in any other calendar year; (ii) a reimbursement (or right thereto) may not be exchanged or liquidated for another benefit or payment; and (iii) reimbursement shall be made no later than the end of the calendar year following
the calendar year in which the Executive incurred the related expense. 
 (g) Temporary Travel and Housing Expenses. The
Company shall reimburse the Executive (on a fully grossed up, tax neutral basis) for reasonable expenses incurred by the Executive in connection with (i) his travel from his home in Newton, Massachusetts to New Haven, Connecticut; (ii) the
lease by the Executive of an apartment in New Haven, Connecticut, and additional expenses associated with such lease including, but not limited to, utilities and insurance (the “Housing Expenses”) provided, however, that reimbursement of
such Housing Expenses shall not exceed $2,000 per month; and (iii) the purchase by the Executive of household furnishings (the “Furnishing Expenses”), provided, however, that reimbursement of such Furnishing Expenses shall not exceed
$10,000. The expenses under this Paragraph 4(g) shall be reimbursed upon submission to the Company by the Executive of invoices containing original receipts of such expenditures. If any of the foregoing expense reimbursements are not exempt from
Section 409A of the United States Tax Code, (i) any reimbursement in one calendar year shall not affect the amount that may be reimbursed in any other calendar year; (ii) a reimbursement (or right thereto) may not be exchanged or
liquidated for another benefit or payment; and (iii) reimbursement shall be made no later than the end of the calendar year following the calendar year in which the Executive incurred the related expense. 

  

			
	Leuchtenberger Employment Agreement	  	3

 5. Termination Benefits. If the Executive’s employment is terminated by the
Company without Cause, or by the Executive with Good Reason, if the Executive dies, or becomes Disabled and the Executive is thereafter terminated (the “Termination”), provided that within sixty (60) days following the date the
termination of the Executive’s employment becomes effective, the Executive executes a severance agreement and mutual release of claims in a form reasonably satisfactory to the Company (the “Release”), and the Release becomes binding
and non-revocable within that time, the Company shall pay to the Executive 
 (a) no later than the sixtieth (60) day
following the date the termination of the Executive’s employment became effective (A) twelve (12) months of his Base Salary (at the rate in effective immediately prior to the Termination) if the Termination occurs on or before the
second anniversary of the Commencement Date; or (B) eighteen (18) months of his Base Salary (at the rate in effective immediately prior to the Termination) if the Termination occurs after the second anniversary of the Commencement Date
(each, the “Salary Continuation Period”), in one lump-sum amount (less required withholdings); 
 (b) the pro-rata
portion of the Annual Bonus for the year in which the termination of the Executive’s employment occurs, payable no later than March 1 of the following year, in one lump-sum amount (less required withholdings); and 

(c) if the Executive elects continuing group medical coverage pursuant to the Consolidated Omnibus Budget Reconciliation Act of 1985, as
amended (“COBRA”), reimbursement of the employer portion of the costs (consistent with the Company’s policy for active employees) of such continuation coverage until the later of (i) the end of the Salary Continuation Period; or
(ii) the date that the Executive is eligible for coverage under another group health plan, subject to the terms of the Company’s plan and applicable law. 
 Except as provided for in this Paragraph 5, the Executive acknowledges that the Company shall have no further obligation to the Executive under this Agreement. 

For purposes of this Agreement, “Cause” means the Company terminated the Executive’s employment because the Executive:
(i) willfully failed to follow lawful, written directions communicated to him by the Board of Directors; (ii) willfully engaged in conduct which is materially injurious to the Company, monetarily or otherwise; (iii) acted with
material dishonesty or materially breached any fiduciary duty owed to the Company; (iv) was convicted of, pleaded guilty to or confessed to an act of fraud, misappropriation or embezzlement or to any felony; (v) used illegal substances at
any time; or (vi) materially breached this Agreement or the Non-Disclosure and Developments Agreement, provided that the Company first notified the Executive in writing of the acts or omissions constituting Cause under (i), (ii), (iii) or
(vi) and the Executive failed to cure such acts or omissions (if curable) within thirty (30) days of receiving the Company’s notice. 

  

			
	Leuchtenberger Employment Agreement	  	4

 For purposes this Agreement, “Good Reason” means the Executive
resigned his employment because the Company: (i) materially diminished the Executive’s Base Salary; (ii) materially diminished the Executive’s authority, duties or responsibilities as President and Chief Executive Officer;
(iii) required the Executive to relocate permanently to an office more than fifty (50) miles from New Haven, Connecticut without the Executive’s consent; or (iv) materially breached the terms of this Agreement, provided that with
respect to (i), (ii), (iii), or (iv), the Executive’s resignation for Good Reason will only become effective if the Company fails to cure the acts or omissions giving rise to a resignation of the Executive’s employment for Good Reason with
thirty (30) days of receiving written notice from the Executive stating his intent to resign his employment for Good Reason and specifying the Company’s acts or omissions under the applicable provision giving rise to a resignation of his
employment for Good Reason. The Executive must provide this notice to the Company within ninety (90) days of the date the acts or omissions giving rise to a resignation of his employment for Good Reason first arise. The Executive’s
resignation shall become effective on the thirty-first
(31st) day following the date the Company receives
the Executive’s written notice. 
 For purposes of this Agreement, “Disabled” means (i) the Executive is not
able to engage in any substantial gainful activity by reason of any medically determinable physical or mental impairment which can be expected to result in death or can be expected to last for a continuous period of not less than 12 months, or
(ii) by reason of any medically determinable physical or mental impairment which can be expected to result in death or can be expected to last for a continuous period of not less than 12 months, the Executive is receiving income replacement
benefits for a period of not less than three months under an accident or health plan covering employees of the Company. 
 (d)
Separation of Service. This Paragraph 5 is intended to be an involuntary separation pay plan, with respect to a termination without Cause or for Good Reason, pursuant to Treas. Reg. §1.409A-1(b)(9)(iii), and constitutes a short term
deferral pursuant to Treas. Reg. § 1.409A-1(b)(4), and thus not “nonqualified deferred compensation” subject to Section 409A of the Tax Code. If this Paragraph 5 is deemed to provide benefits that are deemed to be
“nonqualified deferred compensation” with respect to a termination for Cause, for Good Reason, or any other termination of employment, then the following interpretations apply to this Paragraph 5. Any termination of the Executive’s
employment under Paragraph 5 of this Agreement triggering payment of benefits must constitute a “separation from service” under Section 409A(a)(2)(A)(i) of the Code and Treas. Reg. §1.409A-1(h) before distribution of such
benefits can commence. To the extent that the termination of the Executive’s employment does not constitute a separation of service under Section 409A(a)(2)(A)(i) of the United States Tax Code (the “Code”) and Treas. Reg.
§1.409A-1(h) (as the result of further services that are reasonably anticipated to be provided by the Executive to the Company at the time the Executive’s employment terminate), any benefits payable under Paragraph 5 that constitute
deferred compensation under Section 409A of the Code shall be delayed until after the date of a subsequent event constituting a separation of service under Section 409A(a)(2)(A)(i) of the Code and Treas. Reg. §1.409A-1(h). For
purposes of clarification, this paragraph shall not cause any forfeiture of benefits on the Executive’s part, but shall only act as a delay until such time as a “separation from service” occurs. Further, if the Executive is a
“specified employee” (as that term is used in Section 409A of the Code and regulations and other guidance issued thereunder) on the date his separation from service becomes effective and the payment of the amounts described in
Paragraph 5 constitute non-qualified deferred compensation, the payment of which would result in penalties under Section 409A of the Code, then such payments shall be delayed 

  

			
	Leuchtenberger Employment Agreement	  	5

 
until the business day following the six-month anniversary of the date his separation from service becomes effective, but only to the extent necessary to avoid such penalties under
Section 409A of the Code. On the business day following the six-month anniversary of the date his separation from service becomes effective, the Company shall pay the Executive in a lump sum the aggregate value of the non-qualified deferred
compensation that the Company otherwise would have paid the Executive prior to that date under Paragraph 5 of this Agreement. It is intended that each installment of the payments and benefits provided under Paragraph 5 of this Agreement shall be
treated as a separate “payment” for purposes of Section 409A of the Code. Neither the Company nor the Executive shall have the right to accelerate or defer the delivery of any such payments or benefits except to the extent
specifically permitted or required by Section 409A of the Code. 
 6. Confidentiality and Restrictive Covenants. As
a condition of employment, the Executive must execute the attached Company Non-Disclosure and Developments Agreement. 
 7.
Disputes. 
 (a) Arbitration. The Executive and the Company will arbitrate any and all controversies, claims or
disputes arising out of or relating to this Agreement or the Executive’s employment with the Company (“Claims”) before the American Arbitration Association (“AAA”) before a single arbitrator in accordance with the AAA’s
National Rules for the Resolution of Employment Disputes. The arbitration shall be held in New Haven, Connecticut. The Executive waives any right to a trial by jury in any controversy, claim or dispute with the Company, including those that arise
under any federal, state or local law, including without limitation, claims of harassment, discrimination or wrongful termination under common law or under Title VII of the Civil Rights Act of 1964, the Civil Rights Act of 1991, the Americans with
Disabilities Act, the Age Discrimination in Employment Act, the Older Workers’ Benefit Protection Act. 
 (b)
Non-Disclosure and Developments Agreement. Notwithstanding the provisions of Paragraph 7(a), the Company shall not be compelled to arbitrate claims arising under the Non-Disclosure and Developments Agreement and may institute judicial
proceedings to enforce that agreement pursuant to Section 11 of that agreement. 
 (c) Administrative Claims. While
this Agreement precludes the Executive from filing a court action for any Claim against the Company, this Agreement does not prohibit the Executive from filing an administrative charge with a local, state or federal administrative body. 

8. Miscellaneous. 
 (a) Successors; Binding Agreement. This Agreement and the obligations of the Company hereunder and all rights of the Executive hereunder shall inure to the benefit of the parties hereto and their
respective heirs, personal representatives, successors and assigns, provided, however, that the duties of the Executive hereunder are personal to the Executive and may not be delegated or assigned by him. 

  

			
	Leuchtenberger Employment Agreement	  	6

 (b) Notice. All notices of termination and other communications provided for in this
Agreement shall be in writing and shall be deemed to have been duly given when delivered by hand or mailed by United States registered mail, return receipt requested, addressed as follows: 

If to the Company: 
 Rib-X Pharmaceuticals, Inc. 
 Attn: Secretary of the Board

 300 George Street, Suite 301 

New Haven, CT 06511 
 With a copy to: 
 Daniel Follansbee, Esq. 

Mintz, Levin, Cohn, Ferris, Glovsky and Popeo, P.C. 

One Financial Center 
 Boston, MA 02111 
 If to the Executive: 

20 Old Farm Road 
 Newton, Massachusetts 02459 
 With a copy to: 

Russell Conn, Esq. 
 Conn Kavanaugh Rosenthal Peisch & Ford, LLP 
 Ten Post
Office Square 
 Boston, MA 02109 
 or to such other address as either party may designate by notice to the other, which notice shall be deemed to have been given upon receipt. 

(c) Governing Law. This Agreement shall be governed by and construed in accordance with the laws of the State of Delaware without
regard to the conflict of law rules thereof. 
 (d) Waivers. The waiver of either party hereto of any right hereunder or
of any failure to perform or breach by the other party hereto shall not be deemed a waiver of any other right hereunder or of any other failure or breach by the other party hereto, whether of the same or a similar nature or otherwise. No waiver
shall be deemed to have occurred unless set forth in writing executed by or on behalf of the waiving party. No such written waiver shall be deemed a continuing waiver unless specifically stated therein, and each such waiver shall operate only as to
the specific term or condition waived and shall not constitute a waiver of such term or condition for the future or as to any act other than that specifically waived. 

  

			
	Leuchtenberger Employment Agreement	  	7

 (e) Validity. The invalidity or unenforceability of any provision of this Agreement
shall not affect the validity or enforceability of any other provision of this Agreement, which shall otherwise remain in full force and effect. Moreover, if any one or more of the provisions contained in this Agreement is held to be excessively
broad as to duration, scope or activity, such provisions shall be construed by limiting and reducing them so as to be enforceable to the maximum extent compatible with applicable law. 

(f) Professional Fees. The Company shall reimburse the Executive for the Executive’s reasonable professional fees and costs
(not to exceed $10,000) incurred during 2010 in connection with legal and financial advice pertaining to and negotiation of this Agreement and the transition of his employment to the Company, upon presentation to the Company of bills or invoices for
such services and such other supporting information as the Company may reasonably require. Such payment or reimbursement shall be made no later than thirty (30) days following presentation to the Company of the bill or invoice for such
services. 
 (g) Counterparts. This Agreement may be executed in several counterparts, each of which shall be deemed an
original, but all of which shall constitute one and the same instrument. 
 (h) Entire Agreement. This Agreement, the
Non-Disclosure and Developments Agreement and any grant agreement awarding options under the Plan collectively set forth the entire agreement and understanding of the parties in respect of the subject matter contained herein and therein, and
supersede all prior agreements, promises, covenants, arrangements, communications, representations or warranties, whether oral or written, by any officer, employee or representative of either party in respect of said subject matter. 

(i) Modifications. This Agreement may only be modified in a writing signed by both the Company and the Executive. 

(j) Headings Descriptive. The headings of .the several paragraphs of this Agreement are inserted for convenience only and shall
not in any way affect the meaning or construction of any of this Agreement. 
 (k) Capacity. The Executive represents and
warrants that he is not a party to any agreement that would prohibit him from entering into this Agreement or performing fully his obligations hereunder. 
 Signature page follows 

  

			
	Leuchtenberger Employment Agreement	  	8

 IN WITNESS WHEREOF, the Company and the Executive have executed this Agreement as of the
date first written above. 
  

							
	MARK LEUCHTENBERGER	 		 	RIB-X PHARMACEUTICALS, INC.
				
	/s/    Mark Leuchtenberger	 		 	By:	 	/s/    Jonathan Leff       
		 		 		 	Name: Jonathan Leff
		 		 		 	 Title: Chairmain, Executive Committee
 of Board of Directors

  

			
	Leuchtenberger Employment Agreement	  	9Non-statutory stock option agreement

 Exhibit 10.16 
 Execution Copy 
 NON-STATUTORY STOCK OPTION AGREEMENT 

THIS STOCK OPTION AGREEMENT (this “Agreement”), effective as of the 19th day of March 2010 (the “Grant Date”), is
between Rib-X Pharmaceuticals, Inc., a Delaware corporation (the “Company”), and Mark Leuchtenberger (“Participant”). 
 R E C I T A L S 
 WHEREAS,
on ______, 2001, the Company adopted the Rib-X Pharmaceuticals, Inc. 2001 Stock Option and Incentive Plan (the “Plan”) to provide a flexible vehicle through which it may offer equity-based compensation incentives in the form of restricted
stock and options to purchase shares of the Company’s Common Stock (the “Common Stock”) and other stock-based awards to key personnel, collaborators or consultants of the Company in order to attract, motivate, reward and retain such
personnel and to further align the interests of such personnel with those of the stockholders of the Company; and 
 WHEREAS,
subject to the satisfaction of the conditions set forth herein, the Company desires to grant to the Participant a stock option to purchase shares of Common Stock, and the Participant is willing to accept such option, upon the terms and conditions
hereinafter set forth. 
 NOW, THEREFORE, the parties hereto, in consideration of the mutual covenants contained herein, agree
as follows: 
 1. Option. The Company hereby grants to the Participant an unvested option (the “Option”) to
purchase up to 13,339,196 shares of Common Stock (the “Option Shares”). The exercise price of the Option Shares shall be the fair market value of the Common Stock as determined by the Company’s Board of Directors following receipt of
the Company’s valuation conducted by Grant Thornton as of December 31, 2009 (the “Exercise Price”). The Option shall be subject to the terms and provisions of this Agreement and of the Plan, which is incorporated herein by
reference. Capitalized terms used herein and not defined in this Agreement shall have the meanings specified in the Plan. 
 2.
Vesting. The Option shall vest and may be exercised, in whole or in part, through the tenth anniversary of the Grant Date in accordance with the following schedule: 

 

	 	(a)	25% of the Option shall vest and become exercisable on the first anniversary of the Grant Date; and, thereafter 

 

	 	(b)	 the remaining 75% of the Option shall vest and become exercisable at the rate of 1/48th of the Option per month on each monthly anniversary of the Grant Date such that 100% of the Option shall be vested
fully on the fourth anniversary of the Grant Date. 

 All unvested Options shall immediately vest and become exercisable upon
the effective date of a Change in Control. 

 As used herein, “Change in Control” means that through one transaction or a series of related
transactions, any one person, or more than one person acting as a group (i) acquired ownership of stock of the Company that, together with the stock held by such person or group, constitutes more than 85% of the total fair market value or total
voting power of the stock of the Company (unless such persons or group already owns fifty 50% of the stock of the Company); or (ii) acquired (or has acquired during the 12-month period ending on the date of the most recent acquisition of such
person or persons) at least 85% of the assets from the Company. Notwithstanding the foregoing, “Change in Control” shall not include any change for reasons of (i) bankruptcy, insolvency, or otherwise for the benefit of the
Company’s creditors, or (ii) any debt or equity financing approved by the Board in which an investor or investors receive(s) debt or equity securities from the Company or an affiliate of the Company 

3. Term. The Option, to the extent not previously exercised, shall terminate and become unexercisable upon the earliest of the
following dates (such earliest date the “Termination Date”): 
 (a) the tenth anniversary of the Grant Date;

 (b) the first anniversary of the date of the termination of the Participant’s employment with the Company in the event
that such termination is by reason of the Participant’s Disability or death; 
 (c) ninety (90) calendar days after
the date the Participant’s employment with the Company terminates for any reason other than for Cause, the Participant’s Disability or the Participant’s death; and 

(d) the commencement of business on the date the Participant’s employment with the Company terminates for Cause. 

The period from the Grant Date through and including the Termination Date is hereinafter referred to as the “Term.” 

The term “Disability” shall have the meaning set forth in the Plan. 
 4. Manner of Exercising Option. This Option may be exercised in whole or in part by delivery to the Company, from time to time, of a written notice in substantially the form set forth in Exhibit A
hereto, signed by the Participant (or, in the event of the Participant’s death or other incapacity, by beneficiary designation, bequest or inheritance), specifying the number of Option Shares that the Participant then desires to purchase,
together with cash, certified check, or bank draft payable to the order of the Company, for an amount of United States dollars equal to the Exercise Price plus the Company’s withholding obligations in connection with the delivery of the Option
Shares. 
 5. Insider Trading. The exercise of this Option shall subject the Participant to the Company’s Insider
Trading Policy, as such policy may exist from time to time. 

  

					
	Leuchtenberger Option Agreement	  	2	  	

 6. Tax Treatment. Upon exercise of the Option, the amount that is the difference
between the Exercise Price and the fair market value of the Option Shares on the date of exercise may be subject to withholding. The Company cannot provide you with individual tax advice. The Company advises you to consult with an independent tax
advisor. 
 7. No Transfer or Assignment. Except as set forth in the Plan, the Option, and any rights pertaining thereto,
shall be exercisable only by the Participant, or his legal representative, and neither this Option nor any rights pertaining thereto shall be transferable or assignable in any respect. 

8. Compliance with Laws and Regulations. 
 (a) The Company will not be obligated to issue or deliver shares of Common Stock unless the issuance and delivery of such shares complies with applicable law, including, without limitation, the Securities
Act, the Securities Act of 1934, as amended, applicable state law and the requirements of any stock exchange or market upon which the Common Stock may then be listed, and shall be further subject to the approval of counsel for the Company with
respect to such compliance. 
 (b) In connection with the exercise of this Option, the Participant will execute and deliver to
the Company such representations in writing as may be requested by the Company that it may comply with the applicable requirements of federal and state securities laws. 
 (c) No Option Shares shall be purchased or sold unless and until (i) any then applicable requirements of state or federal laws and regulatory agencies shall have been fully complied with to the
satisfaction of the Company and its counsel, and (ii) if required to do so by the Company, the Participant shall have executed and delivered to the Company a letter of investment intent in such form and containing such provisions as the
Committee may require. 
 9. Notices. All notices, requests, demands, waivers, consents, approvals or other
communications pursuant to this Agreement shall be in writing and delivered to the Company at its principal executive offices, Attention: Secretary, or to the Participant at the residence address reflected in the records maintained by the Company.

 10. No Rights of Stockholder. Neither the Participant nor any legal representative of the Participant shall be, or
have any of the rights and privileges of, a stockholder of the Company with respect to any Option Shares except to the extent that certificates for such Option Shares shall have been issued upon the exercise of the Option as provided for in this
Agreement and under the terms of the Plan. 
 11. Construction. The Committee shall have exclusive authority to interpret
and construe the Option, and its determinations with respect thereto shall be final and binding on the Company and the Participant. In the event of any conflict between the Plan and this Agreement, the terms of the Plan shall control. Capitalized
terms in this Agreement that are not otherwise defined have the meaning assigned to them in the Plan. 

  

					
	 Leuchtenberger Option Agreement
	  	3	  	

 12. No Rights Conferred. Nothing contained in this Agreement shall confer upon the
Participant any right with respect to the continuation of his or her Service with the Company or its subsidiaries or interfere in any way with the right of the Company and its subsidiaries at any time to terminate such Service or to increase or
decrease, or otherwise adjust, the other terms and conditions of the Participant’s Service. 
 13. Entire Agreement;
Amendment. This Agreement and the Plan sets forth the entire understanding of the parties hereto with respect to the subject matter hereof and may not be amended or supplemented except by a written instrument executed by each of the parties
hereto. 
 14. Governing Law. This Agreement shall be governed by and construed in accordance with the laws of the State
of Delaware, without regard to its principles of conflict of laws. 
 Signature page follows 

  

					
	Leuchtenberger Option Agreement	  	4	  	

 IN WITNESS WHEREOF, the Company has caused this Agreement to be executed by its duly
authorized officer, and the Participant has executed this Agreement, as of the day and year above written. 
  

									
	RIB-X PHARMACEUTICALS, INC.	 		 		 	PARTICIPANT
					
	By:	 	/s/     Jonathan Leff	 		 		 	/s/     Mark Leuchtenberger
		 	Name: Jonathan Leff	 		 		 	Mark Leuchtenberger
		 	Title:   Chairman, Executive	 		 		 	
		 	            Committee of Board of Directors	 		 		 	

  

					
	Leuchtenberger Option Agreement	  	5	  	

 EXHIBIT A 
 NOTICE OF EXERCISE OF STOCK OPTION 
 I hereby exercise my Option granted by Rib-X Pharmaceuticals,
Inc. (the “Company”) and seek to purchase ________ shares of common stock of the Company. I understand that this exercise is subject to all the terms and provisions of my Stock Option Agreement and the Rib-X Pharmaceuticals, Inc. 2001
Stock Option and Incentive Plan. 
 Enclosed is my check in the sum of $___________ in payment for such shares. 

Also enclosed in my check in the sum of $_______ to satisfy the Company’s payroll and income tax withholding requirements. 

I acknowledge that the shares are not being registered under the Securities Act, based, in part, in reliance upon an exemption from registration under
Securities and Exchange Commission Rule 701 promulgated under the Securities Act, and a comparable exemption from qualification under applicable state securities laws, as each may be amended from time to time. I hereby make the following
representations to the Company and acknowledge that the Company’s reliance on federal and state securities law exemptions from registration and qualification is predicated, in substantial part, upon the accuracy of these representations:

  

	 	•	 	 I am acquiring the shares solely for my own account, for investment purposes only, and not with a view to or an intent to sell, or to offer for resale
in connection with any unregistered distribution, all or any portion of the shares within the meaning of the Securities Act and/or any applicable state securities laws. 

 

	 	•	 	 I have had an opportunity to ask questions and receive answers from the Company regarding the restrictions imposed on the shares purchased upon my
exercise of the Option. 

  

	 	•	 	 I have been furnished with, and/or have access to, such information as I consider necessary or appropriate for deciding whether to exercise the Option
and purchase the shares. However, in evaluating the merits and risks of an investment in the shares, I have relied only upon the advice of my own legal counsel, tax advisors, and/or investment advisors. 

 

	 	•	 	 I am aware that any investment in common shares of a closely held corporation such as the Company is non-marketable, is non-transferable and could
require capital to be invested for an indefinite period of time, possibly without return, and at substantial risk of loss. 

  

	 	•	 	 I understand that the shares I acquire on exercise of the Option will be characterized as “restricted securities” under the federal
securities laws, and that, under such laws and applicable regulations, I may resell the shares without registration under the Securities Act only in certain limited circumstances, including in accordance with the conditions of Rule 144 promulgated
under the Securities Act, as presently in effect. I acknowledge receiving a copy of Rule 144 promulgated under the Securities Act, as presently in effect, and represent that I am familiar with this rule, and understand the resale limitations imposed
by the rule, by the Securities Act and by applicable state securities law. 

  

					
	Leuchtenberger Option Agreement	  	1	  	

	 	•	 	 I have read and understand the restrictions and limitations set forth in the Plan and my Stock Option Agreement. 

 

	 	•	 	 I have not relied upon any oral representation made to me relating to the purchase of the shares on my exercise of the Option or upon information
presented in any promotional meeting or material relating to the shares. 

  

	 	•	 	 I understand that the Company has no obligation to register the shares or file any registration statement under federal or state securities laws.

  

	 	•	 	 I understand that the certificates evidencing the shares shall in addition to any other legend required by contract or applicable law bear a legend in
substance as follows: 

 THE SECURITIES REPRESENTED BY THIS CERTIFICATE HAVE BEEN ACQUIRED FOR INVESTMENT AND
HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED, OR PURSUANT TO ANY STATE SECURITIES LAWS. THESE SECURITIES MAY NOT BE SOLD OR TRANSFERRED IN THE ABSENCE OF SUCH REGISTRATION OR AN EXEMPTION THEREFROM UNDER SAID ACT OR LAWS.

 Dated: 
  

	
	
	  
	Participant signature

 Receipt is hereby acknowledged of the delivery to me by Rib-X Pharmaceuticals, Inc. of certificates for ___________
shares of common stock of the Company purchased by me pursuant to the terms and conditions of the Stock Option Agreement referred to above. 

Date: 
  

	
	
	  
	Participant’s Signature

  

					
	Leuchtenberger Option Agreement	  	2

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