Document:

Form of Real Estate Contingent Value Rights Agreement

 Exhibit 10.5 
 Form of Real Estate CVR Agreement 
 CONTINGENT VALUE RIGHTS AGREEMENT 
 THIS CONTINGENT VALUE RIGHTS AGREEMENT, dated as of [ — ], 2009 (this
“Agreement”, is entered into by and among Ligand Pharmaceuticals Incorporated, a Delaware corporation (“Buyer”), Neurogen Corporation, a Delaware corporation
(“Target”), and [ — ], a [ — ], as Rights Agent (the “Rights Agent”) and as initial Real Estate CVR
Registrar (as defined herein). 
 Preamble 
 Buyer, Neon Signal, LLC, a Delaware limited liability company and wholly-owned subsidiary of Buyer (“Sub”), and Target have entered into an Agreement and Plan of Merger dated as of
August 23, 2009 (the “Merger Agreement”), pursuant to which Sub will merge with and into Target (the “Merger”), with Target (or a successor entity) surviving the Merger as a subsidiary of Buyer.

 Pursuant to the Merger Agreement, Buyer agreed to create and issue to Target’s stockholders of record immediately before the
effective time of the Merger, contingent value rights as hereinafter described. 
 The parties have done all things necessary to make the
contingent value rights, when issued pursuant to the Merger Agreement and hereunder, the valid obligations of Buyer and to make this Agreement a valid and binding agreement of Buyer, in accordance with its terms. 
 NOW, THEREFORE, for and in consideration of the premises and the consummation of the transactions referred to above, it is mutually covenanted and
agreed, for the equal and proportionate benefit of all Holders (as hereinafter defined), as follows: 
 ARTICLE I 
 DEFINITIONS 
 Section 1.1.
Definitions. 
 (a) For all purposes of this Agreement, except as otherwise expressly provided or unless the context otherwise requires:

 (i) the terms defined in this Article have the meanings assigned to them in this Article, and include the plural as well as the singular;

 (ii) all accounting terms used herein and not expressly defined herein shall have the meanings assigned to such terms in accordance with
United States generally accepted accounting principles, as in effect on the date hereof; 
 (iii) the words “herein,”
“hereof’ and “hereunder” and other words of similar import refer to this Agreement as a whole and not to any particular Article, Section or other subdivision; 

 (iv) unless the context otherwise requires, words describing the singular number shall include the
plural and vice versa, words denoting any gender shall include all genders and words denoting natural Persons shall include corporations, partnerships and other Persons and vice versa; and 
 (v) all references to “including” shall be deemed to mean including without limitation. 
 (b) Capitalized terms used but not otherwise defined herein shall have the meanings ascribed thereto in the Merger Agreement. The following terms shall
have the meanings ascribed to them as follows: 
 “Achievement Certificate” has the meaning set forth in
Section 2.4(a). 
 “Board of Directors” means the board of directors of Buyer. 
 “Board Resolution” means a copy of a resolution certified by the secretary or an assistant secretary of Buyer to have been duly adopted
by the Board of Directors and to be in full force and effect on the date of such certification, and delivered to the Rights Agent. 
 “Business Day” means any day other than a Saturday, Sunday or a day on which banking institutions in New York, New York are authorized or obligated by law or executive order to remain closed. 
 “CVR Outside Date” means [insert date that is six months from the Effective Date]. 
 “Holder” means a Person in whose name a Real Estate CVR is registered in the Real Estate CVR Register. 
 “Non-Achievement Certificate” has the meaning set forth in Section 2.4(b). 
 “Notice of Objection” has the meaning set forth in Section 2.4(d). 
 “Objection Period” has the meaning set forth in Section 2.4(d). 
 “Officer’s Certificate” means a certificate signed by the chief executive officer, president, chief financial officer, any vice
president, the controller, the treasurer or the secretary, in each case, of Buyer, in his or her capacity as such an officer, and delivered to the Rights Agent. 
 “Permitted Transfer” means: (i) the transfer of any or all of the Real Estate CVRs (upon the death of the Holder) by will or intestacy; (ii) transfer by instrument to an inter vivos or
testamentary trust in which the Real Estate CVRs are to be passed to beneficiaries upon the death of the trustee; (iii) transfers made pursuant to a court order of a court of competent jurisdiction (such as in connection with divorce,
bankruptcy or liquidation); (iv) if the Holder is a partnership or limited liability company, a distribution by the transferring partnership or limited liability company to its partners or members, as applicable; (v) a transfer made by
operation of law (including a consolidation or merger) or in connection with the dissolution, liquidation or termination of any corporation, limited liability company, partnership or other entity; (vi) a transfer from a participant’s
account in a tax-qualified employee benefit plan to the participant or to such participant’s account in a different tax-qualified employee benefit plan or to a tax-qualified 

  

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individual retirement account for the benefit of such participant; or (vii) a transfer from a participant in a tax-qualified employee benefit plan, who
received the Real Estate CVRs from such participant’s account in such tax-qualified employee benefit plan, to such participant’s account in a different tax-qualified employee benefit plan or to a tax-qualified individual retirement account
for the benefit of such participant. 
 “Person” means any natural person, corporation, partnership, limited liability
company, trust, estate, other firm or entity, or governmental body. 
 “Real Estate CVR Payment Amount” means an
amount equal to the aggregate cash proceeds received by Buyer, or any of its subsidiaries, after the Effective Time and before the CVR Outside Date, from any purchaser (other than Buyer) of the Real Estate, less (i) any out-of-pocket costs and
expenses reasonably incurred by the Buyer (taking into account any lease payments received by Buyer after the Effective Time), or any of its subsidiaries, in connection with the holding or the sale of the Real Estate (including the payment of the
principal of and interest on any debt secured by the Real Estate at the Effective Time, commissions and amounts paid to the Consulting Committee in accordance with an arrangement entered into pursuant to Section 5.15(b) of the Merger Agreement,
and incremental costs and expenses related to management of the risk of environmental liability pertaining to the Real Estate and/or assurance of potential buyers regarding the same, such as preparing an addendum to the environmental assessments
which may include sampling, and revisions to Buyer’s environmental insurance policy), and (ii) any amounts previously paid to the Holders pursuant to the Real Estate CVRs. For the avoidance of doubt, any amounts deducted from Net Cash
Amount as accounts payable relating to the Real Estate shall not be considered “costs and expenses” incurred by Buyer hereunder. 
 “Real Estate CVR Payment Date” means the date or dates (if any and if ever) that a Real Estate CVR Payment Amount is payable by Buyer to the Holders, which date shall be established pursuant to Section 2.4. 

“Real Estate CVR Payment Event” means the receipt by Buyer of cash proceeds from any purchaser (other than Buyer) of all, or any
parcel, of the Real Estate. 
 “Real Estate CVR Register” has the meaning set forth in Section 2.3(b). 
 “Real Estate CVR Registrar” has the meaning set forth in Section 2.3(b). 
 “Real Estate CVRs” means the Real Estate Contingent Value Rights issued by Buyer pursuant to the Merger Agreement and this Agreement.

 “Real Estate Sale” means the sale of all, or any parcel, of the Real Estate to a Person other than Buyer. 
 “Rights Agent” means the Rights Agent named in the first paragraph of this Agreement, until a successor Rights Agent shall have become
such pursuant to the applicable provisions of this Agreement, and thereafter “Rights Agent” shall mean such successor Rights Agent. 
 “Rights Agent Fee” means the agreed-upon fee of the Rights Agent to act in such capacity pursuant to the terms of this Agreement. 
 “Surviving Person” has the meaning set forth in Section 6.1(a)(i). 
  

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 ARTICLE II 
 CONTINGENT VALUE RIGHTS 
 Section 2.1. Issuance of Real Estate CVRs; Appointment of Rights
Agent. 
 (a) The Real Estate CVRs shall be issued pursuant to the Merger Agreement at the time and in the manner set forth in the Merger
Agreement. 
 (b) Buyer hereby appoints [ — ] as the Rights Agent to act as rights agent for
Buyer in accordance with the instructions hereinafter set forth in this Agreement, and the Rights Agent hereby accepts such appointment. 
 Section 2.2. Nontransferable. 
 The Real Estate CVRs shall not be sold, assigned, transferred, pledged, encumbered or in
any other manner transferred or disposed of, in whole or in part, other than through a Permitted Transfer. 
 Section 2.3. No
Certificate; Registration; Registration of Transfer; Change of Address. 
 (a) The Real Estate CVRs shall not be evidenced by a
certificate or other instrument. 
 (b) The Rights Agent shall keep a register (the “Real Estate CVR Register”) for
the registration of Real Estate CVRs. The Rights Agent is hereby initially appointed “Real Estate CVR Registrar” for the purpose of registering Real Estate CVRs and transfers of Real Estate CVRs as herein provided. Upon any
change to the identity of the Rights Agent, the successor Rights Agent shall automatically also become the successor Real Estate CVR Registrar. 
 (c) Subject to the restriction on transferability set forth in Section 2.2, every request made to transfer a Real Estate CVR must be in writing and accompanied by a written instrument or instruments of transfer and any other requested
documentation in a form reasonably satisfactory to Buyer and the Real Estate CVR Registrar, duly executed by the registered Holder or Holders thereof or by the duly appointed legal representative thereof or by a duly authorized attorney, such
signature to be guaranteed by a participant in a recognized Signature Guarantee Medallion Program. A request for a transfer of a Real Estate CVR shall be accompanied by such documentation establishing that the transfer is a Permitted Transfer as may
be reasonably requested by Buyer and/or the Real Estate CVR Registrar (including opinions of counsel), if appropriate. Upon receipt of such written request and materials, the Real Estate CVR Registrar shall, subject to its reasonable determination
that the transfer instrument is in proper form and the transfer otherwise complies with the other terms and conditions herein, register the transfer of the Real Estate CVRs in the Real Estate CVR Register. All duly transferred Real Estate CVRs
registered in the Real Estate CVR Register shall be the valid obligations of Buyer, evidencing the same right and shall entitle the transferee to the same benefits and rights under this Agreement, as those previously held by the transferor. No
transfer of a Real Estate CVR shall be valid until registered in the Real Estate CVR Register, and any transfer not duly registered in the Real Estate CVR Register will be void ab initio. Any transfer or assignment of the Real Estate CVRs shall be
without charge (other than the cost of any transfer tax which shall be the responsibility of the transferor) to the Holder. 
  

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 (d) A Holder may make a written request to the Real Estate CVR Registrar to change such Holder’s
address of record in the Real Estate CVR Register. The written request must be duly executed by the Holder. Upon receipt of such written notice, the Real Estate CVR Registrar shall promptly record the change of address in the Real Estate CVR
Register. 
 Section 2.4. Payment Procedures. 
 (a) Promptly following the occurrence of any Real Estate CVR Payment Event, but in no event later than five Business Days after the occurrence of such Real Estate CVR Payment Event, Buyer shall deliver to the Rights
Agent a certificate (the “Achievement Certificate”), certifying that the Holders are entitled to receive such Real Estate CVR Payment Amount. No transaction described in Section 6.1(a) hereof shall give the Holders the
right to receive the Real Estate CVR Payment Amount. 
 (b) If a Real Estate Sale has not occurred on or before the CVR Outside Date, then,
within five Business Days after the CVR Outside Date, Buyer shall deliver to the Rights Agent a certificate (the “Non-Achievement Certificate”), stating that a Real Estate Sale has not occurred on or before the CVR Outside
Date and no Real Estate CVR Payment Event can occur. 
 (c) Except as otherwise requested by any Holder, the Rights Agent shall promptly (and
in no event later than five Business Days after receipt thereof) send each Holder a copy of any Achievement Certificate or Non-Achievement Certificate at its registered address. 
 (d) Upon demand by any Holder or Holders of at least 20% in the aggregate of the outstanding Real Estate CVRs within 45 calendar days after
distribution by the Rights Agent of a Non-Achievement Certificate (the “Objection Period”), the Rights Agent shall deliver a written notice to Buyer prepared by such Holder or Holders specifying that such Holder or Holders
object to the determination of Buyer that a Real Estate Sale did not timely occur (a “Notice of Objection”) and stating the reason upon which such Holder or Holders have determined that a Real Estate Sale has occurred on or
before the CVR Outside Date. Any dispute arising from a Notice of Objection shall be resolved in accordance with the procedure set forth in Section 7.12, which decision shall be binding on the parties hereto and every Holder (including Holders
not participating therein). 
 (e) If a Notice of Objection has not been delivered to Buyer within the Objection Period, then the Holders
shall have no right to receive the Real Estate CVR Payment Amount, and Buyer and the Rights Agent shall have no further obligations with respect to the Real Estate CVR Payment Amount. 
 (f) If Buyer delivers an Achievement Certificate to the Rights Agent or if the Real Estate CVR Payment Amount is determined to be payable pursuant to
Section 2.4(d) above, Buyer shall establish a Real Estate CVR Payment Date that is within 15 calendar days of the date of the Achievement Certificate or the date of final determination pursuant to Section 2.4(d) above, as applicable. At
least five Business Days before such Real Estate CVR Payment Date, Buyer shall cause the Real Estate CVR Payment Amount to be delivered to the Rights Agent, who will in turn, on the Real Estate CVR Payment Date, distribute the Real Estate CVR
Payment Amount to the Holders (each Holder being entitled to receive its pro rata share of the Real Estate CVR Payment Amount based on the number of Real Estate CVRs held (as of the date of the Achievement Certificate or the date of final
determination pursuant to Section 2.4(d) above, as applicable) by such Holder as reflected on the Real Estate CVR Register) (i) by check mailed to 

  

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the address of each such respective Holder as reflected in the Real Estate CVR Register as of the close of business on the last Business Day before such Real
Estate CVR Payment Date, or, (ii) with respect to any Holder that is due payment pursuant to this Agreement in excess of $1,000,000 who has provided the Rights Agent with wire transfer instructions, by wire transfer of immediately available
funds to such account. 
 (g) Buyer shall be entitled to deduct and withhold, or cause to be deducted or withheld, from each Real Estate CVR
Payment Amount otherwise payable pursuant to this Agreement, such amounts as Buyer or the applicable subsidiary of Buyer is required to deduct and withhold with respect to the making of such payment under the Internal Revenue Code, or any provision
of state, local or foreign tax law. To the extent that amounts are so withheld or paid over to or deposited with the relevant governmental entity, such withheld amounts shall be treated for all purposes of this Agreement as having been paid to the
Holder in respect of which such deduction and withholding was made. 
 (h) Subject to prior execution and delivery by the Rights Agent of a
reasonable and customary confidentiality/nonuse agreement, Buyer shall promptly furnish to the Rights Agent all information and documentation in connection with this Agreement and the Real Estate CVRs that the Rights Agent or any Holder or Holders
of at least 5% in the aggregate of the outstanding Real Estate CVRs may reasonably request in connection with the determination of whether the Real Estate CVR Payment Event has occurred. Subject to prior execution and delivery by the applicable
Holders of a reasonable and customary confidentiality/nonuse agreement, the Rights Agent shall forward any information and documentation it receives to the Holders who request such information. 
 Section 2.5. No Voting, Dividends or Interest; No Equity or Ownership Interest in Buyer. 
 (a) The Real Estate CVRs shall not have any voting or dividend rights, and interest shall not accrue on any amounts payable on the Real Estate CVRs to any
Holder. 
 (b) The Real Estate CVRs shall not represent any equity or ownership interest in Buyer or in any constituent company to the
Merger. 
 Section 2.6. Sole Discretion and Decision Making Authority; No Fiduciary Duty. 
 Notwithstanding anything else in this Agreement to the contrary, Buyer shall attempt to sell the Real Estate for the benefit of the Holders of the Real
Estate CVRs, but shall have sole discretion and decision making authority, which shall be exercised in good faith and with commercial reasonableness, over when (if ever) to consummate the sale of all, or any parcel of the Real Estate, to any
purchaser, and upon what terms and conditions. If Buyer, after engaging in the efforts describe above in this paragraph, is unable to sell the Real Estate, or any parcel thereof, at any price by the CVR Outside Date, then Buyer shall deliver to the
Rights Agent a certificate of an executive officer of Buyer to that effect on the CVR Outside Date.  
  

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 ARTICLE III 
 THE RIGHTS AGENT 
 Section 3.1. Certain Duties and Responsibilities. 
 (a) The Rights Agent shall not have any liability for any actions taken or not taken in connection with this Agreement, except to the extent of its
willful misconduct, bad faith or gross negligence. No provision of this Agreement shall require the Rights Agent to expend or risk its own funds or otherwise incur any financial liability in the performance of any of its duties hereunder or in the
exercise of any of its rights or powers. 
 (b) Any Holder or Holders of at least 20% in the aggregate of the outstanding Real Estate CVRs
may direct the Rights Agent to act on behalf of the Holders in enforcing any of its or their rights hereunder, including, without limitation, the delivery of any Notice of Objection and negotiation or arbitration pursuant to Section 7.12. The
Rights Agent shall be under no obligation to institute any action, suit or legal proceeding or to take any other action likely to involve material expense unless such Holder or Holders shall furnish the Rights Agent with reasonable security and
indemnity for any costs and expenses which may be incurred. All rights of action under this Agreement may be enforced by the Rights Agent, and any action, suit or proceeding instituted by the Rights Agent shall be brought in its name as Rights
Agent, and any recovery of judgment shall be for the ratable benefit of all the Holders, as their respective rights or interests may appear. 
 Section 3.2. Certain Rights of Rights Agent. 
 The Rights Agent undertakes to perform such duties and only such duties
as are specifically set forth in this Agreement, and no implied covenants or obligations shall be read into this Agreement against the Rights Agent. In addition: 
 (a) the Rights Agent may rely and shall be protected in acting or refraining from acting upon any resolution, certificate, statement, instrument, opinion, report, notice, request, direction, consent, order or other
paper or document believed by it to be genuine and to have been signed or presented by the proper party or parties; 
 (b) whenever the
Rights Agent shall deem it desirable that a matter be proved or established before taking, suffering or omitting any action hereunder, the Rights Agent may, in the absence of willful misconduct, bad faith or gross negligence on its part, rely upon
an Officer’s Certificate; 
 (c) the Rights Agent may engage and consult with counsel of its selection and the written advice of such
counsel or any opinion of counsel shall be full and complete authorization and protection in respect of any action taken, suffered or omitted by it hereunder in good faith and in reliance thereon; 
 (d) in the event of arbitration, the Rights Agent may engage and consult with tax experts, valuation firms and other experts and third parties that it,
in its sole and absolute discretion, deems appropriate or necessary to enable it to discharge its duties hereunder; 
 (e) the permissive
rights of the Rights Agent to do things enumerated in this Agreement shall not be construed as a duty; 
 (f) the Rights Agent shall not be
required to give any note or surety in respect of the execution of such powers or otherwise in respect of the premises; 
  

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 (g) Buyer agrees to indemnify the Rights Agent for, and hold the Rights Agent harmless against, any loss,
liability, claim, demands, suits or expense (in each case pertaining to the Rights Agent’s own account only) arising out of or in connection with the Rights Agent’s duties under this Agreement, including the costs and expenses of defending
the Rights Agent against any claims, charges, demands, suits or loss, unless such loss shall have been determined by a court of competent jurisdiction to be a result of the Rights Agent’s willful misconduct, bad faith or gross negligence,
provided, however, that the Rights Agent’s aggregate liability with respect to, arising from, or arising in connection with this Agreement, or from all services provided or omitted to be provided under this Agreement, whether in contract, in
tort, or otherwise, is limited to, and shall not exceed, the amounts paid hereunder by Buyer to the Rights Agent as fees and charges, but not including reimbursable expenses; and 
 (h) Buyer agrees (i) to pay the fees and expenses of the Rights Agent in connection with this Agreement, as set forth on Schedule 1 hereto, and
(ii) to reimburse the Rights Agent for all taxes and governmental charges, reasonable expenses and other charges of any kind and nature incurred by the Rights Agent in the execution of this Agreement (other than taxes measured by the Rights
Agent’s net income). The Rights Agent shall also be entitled to reimbursement from Buyer for all reasonable and necessary out-of-pocket expenses (including reasonable fees and expenses of the Rights Agent’s counsel and agent) paid or
incurred by it in connection with the administration by the Rights Agent of its duties hereunder. An invoice for the Rights Agent Fee will be rendered a reasonable time before, and paid on, the effective date of the applicable transaction. An
invoice for any out-of-pocket expenses and per item fees realized will be rendered and payable within thirty (30) days after receipt by Buyer. Buyer agrees to pay to Rights Agent any amounts, including fees and expenses, payable in favor of the
Rights Agent in connection with any dispute, resolution or arbitration arising under or in connection with the Agreement; provided, however, that in the event of a resolution in favor of Buyer, any amounts, including fees and expenses, payable by
Buyer in favor of the Rights Agent or payable in favor of Buyer related to such dispute, resolution or arbitration shall be offset against the Real Estate CVR Payment Amount, if any, or any payment to be made thereafter under any of the other CVR
Agreements. 
 Section 3.3. Resignation and Removal; Appointment of Successor. 
 (a) The Rights Agent may resign at any time by giving written notice thereof to Buyer specifying a date when such resignation shall take effect, which
notice shall be sent at least 30 days before the date so specified. 
 (b) If the Rights Agent shall resign, be removed or become
incapable of acting, Buyer, by way of a Board Resolution, shall promptly appoint a qualified successor Rights Agent who may (but need not) be a Holder but shall not be an officer of Buyer. The successor Rights Agent so appointed shall, forthwith
upon its acceptance of such appointment in accordance with this Section 3.3(b), become the successor Rights Agent. 
 (c) Buyer shall
give notice of each resignation and each removal of a Rights Agent and each appointment of a successor Rights Agent by mailing written notice of such event by first-class mail, postage prepaid, to the Holders as their names and addresses appear in
the Real Estate CVR Register. Each notice shall include the name and address of the successor Rights Agent. If Buyer fails to send such notice within ten days after acceptance of appointment by a successor Rights Agent, the successor Rights Agent
shall cause such notice to be mailed at the expense of Buyer. 
  

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 Section 3.4. Acceptance of Appointment by Successor. 
 Every successor Rights Agent appointed hereunder shall execute, acknowledge and deliver to Buyer and to the retiring Rights Agent an instrument accepting
such appointment and a counterpart of this Agreement, and thereupon such successor Rights Agent, without any further act, deed or conveyance, shall become vested with all the rights, powers, trusts and duties of the retiring Rights Agent; provided,
that upon the request of Buyer or the successor Rights Agent, such retiring Rights Agent shall execute and deliver an instrument transferring to such successor Rights Agent all the rights, powers and trusts of the retiring Rights Agent and shall
cooperate in the transfer of all relevant data, including the Real Estate CVR Register, to the successor Rights Agent. 
 ARTICLE IV 

 COVENANTS 
 Section 4.1. List of Holders. 
 Buyer shall furnish or cause to be furnished to the Rights Agent in such form as Buyer
receives from its transfer agent (or other agent performing similar services for Buyer), the names, addresses and shareholdings of the Holders, within five Business Days after the effective time of the Merger. 
 Section 4.2. Payment of Real Estate CVR Payment Amount. 
 Buyer shall duly and promptly pay each Real Estate CVR Payment Amount, if any, in immediately available funds, to the Rights Agent to be distributed to the Holders in the manner provided for in Section 2.4 and in
accordance with the terms of this Agreement. 
 Section 4.3. Assignments. 
 Buyer shall not, in whole or in part, assign any of its obligations under this Agreement other than in accordance with the terms of Section 6.1
hereof. 
 ARTICLE V 
 AMENDMENTS 
 Section 5.1. Amendments Without Consent of Holders. 
 (a) Without the consent of any Holders or the Rights Agent, Buyer, when authorized by a Board Resolution, at any time and from time to time, may enter
into one or more amendments hereto, for any of the following purposes: 
 (i) to evidence the succession of another Person to Buyer and the
assumption by any such successor of the covenants of Buyer herein in a transaction contemplated by Section 6.1 hereof; or 
 (ii) to
evidence the termination of the Real Estate CVR Registrar and the succession of another Person as a successor Real Estate CVR Registrar and the assumption by any successor of the obligations of the Real Estate CVR Registrar herein. 
  

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 (b) Without the consent of any Holders, Buyer, when authorized by a Board Resolution, and the Rights
Agent, in the Rights Agent’s sole and absolute discretion, at any time and from time to time, may enter into one or more amendments hereto, for any of the following purposes: 
 (i) to evidence the succession of another Person as a successor Rights Agent and the assumption by any successor of the covenants and obligations of the
Rights Agent herein; 
 (ii) to add to the covenants of Buyer such further covenants, restrictions, conditions or provisions as the Board of
Directors and the Rights Agent shall consider to be for the protection of the Holders; provided, that in each case, such provisions shall not adversely affect the interests of the Holders; 
 (iii) to cure any ambiguity, to correct or supplement any provision herein that may be defective or inconsistent with any other provision herein, or to
make any other provisions with respect to matters or questions arising under this Agreement; provided, that in each case, such provisions shall not adversely affect the interests of the Holders; or 
 (iv) to add, eliminate or change any provision of this Agreement unless such addition, elimination or change is adverse to the interests of the Holders.

 (c) Promptly after the execution by Buyer and the Rights Agent of any amendment pursuant to the provisions of this Section 5.1, Buyer
shall mail a notice thereof by first-class mail to each of the Holders at their addresses as they shall appear on the Real Estate CVR Register, setting forth in general terms the substance of such amendment. 
 Section 5.2. Amendments With Consent of Holders. 
 (a) Subject to Section 5.1 (which amendments pursuant to Section 5.1 may be made without the consent of the Holders), with the consent of the Holders of not less than a majority of the outstanding Real
Estate CVRs, whether evidenced in writing or taken at a meeting of the Holders, Buyer, when authorized by a Board Resolution, and the Rights Agent may enter into one or more amendments hereto for the purpose of adding, eliminating or changing any
provisions of this Agreement, even if such addition, elimination or change is in any way adverse to the interests of the Holders. 
 (b)
Promptly after the execution by Buyer and the Rights Agent of any amendment pursuant to the provisions of this Section 5.2, Buyer shall mail a notice thereof by first-class mail to the Holders at their addresses as they shall appear on the Real
Estate CVR Register, setting forth in general terms the substance of such amendment. 
 Section 5.3. Execution of Amendments.

 In executing any amendment permitted by this Article V, the Rights Agent shall be entitled to receive, and shall be fully protected in
relying upon, an opinion of counsel stating that the execution of such amendment is authorized or permitted by this Agreement. The Rights Agent may, but is not obligated to, enter into any such amendment that affects the Rights Agent’s own
rights, privileges, covenants or duties under this Agreement or otherwise. 
  

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 Section 5.4. Effect of Amendments. 
 Upon the execution of any amendment under this Article V, this Agreement shall be modified in accordance therewith, such amendment shall form a part of
this Agreement for all purposes and every Holder shall be bound thereby. 
 ARTICLE VI 
 CONSOLIDATION, MERGER, SALE OR CONVEYANCE 
 Section 6.1. Buyer May Consolidate, Etc. 
 (a) Buyer shall not consolidate with or merge into any other Person or
convey, transfer or lease its properties and assets substantially as an entirety to any Person, unless: 
 (i) the Person formed by such
consolidation or into which Buyer is merged or the Person that acquires by conveyance or transfer, or that leases, the properties and assets of Buyer substantially as an entirety (the “Surviving Person”) shall expressly
assume payment (if and to the extent required hereunder) of amounts on all the Real Estate CVRs and the performance of every duty and covenant of this Agreement on the part of Buyer to be performed or observed; and 
 (ii) Buyer has delivered to the Rights Agent an Officer’s Certificate, stating that such consolidation, merger, conveyance, transfer or lease
complies with this Article VI and that all conditions precedent herein provided for relating to such transaction have been complied with. 
 (b) In the event Buyer conveys, transfers or leases its properties and assets substantially as an entirety in accordance with the terms and conditions of this Section 6.1, Buyer and the Surviving Person shall be jointly and severally
liable for the payment of the Real Estate CVR Payment Amount and the performance of every duty and covenant of this Agreement on the part of the Buyer to be performed or observed. 
 Section 6.2. Successor Substituted. 
 Upon any consolidation of or merger by Buyer with or into any other Person, or any conveyance, transfer or lease of the properties and assets substantially as an entirety to any Person in accordance with Section 6.1, the Surviving
Person shall succeed to, and be substituted for, and may exercise every right and power of, Buyer under this Agreement with the same effect as if the Surviving Person had been named as Buyer herein, and thereafter the predecessor Person shall be
relieved of all obligations and covenants under this Agreement and the Real Estate CVRs. 
 ARTICLE VII 
 OTHER PROVISIONS OF GENERAL APPLICATION 
 Section 7.1. Notices to Rights Agent and Buyer. 
 Any request, demand, authorization, direction, notice, consent, waiver
or other document provided or permitted by this Agreement shall be sufficient for every purpose hereunder if in writing and sent by facsimile transmission, delivered personally, or by certified or registered mail (return receipt requested and
first-class postage prepaid) or sent by a nationally recognized overnight courier (with proof of service), addressed as follows, and shall be deemed to have been given upon receipt: 
 (a) if to the Rights Agent, addressed to it at [ — ], facsimile at [ —
 ], or at any other address previously furnished in writing to the Holders and Buyer by the Rights Agent in accordance with this Section 7.1; or 
  

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 (b) if to Buyer, addressed to it at 10275 Science Center Drive, San Diego, California 92121, facsimile at
(858) 550-7272, or at any other address previously furnished in writing to the Rights Agent and the Holders by Buyer in accordance with this Section 7.1. 
 Section 7.2. Notice to Holders. 
 Where this Agreement provides for notice to Holders, such
notice shall be sufficiently given (unless otherwise herein expressly provided) if in writing and mailed, first-class postage prepaid, to each Holder affected by such event, at his, her or its address as it appears in the Real Estate CVR Register,
not later than the latest date, and not earlier than the earliest date, prescribed for the giving of such notice. In any case where notice to Holders is given by mail, neither the failure to mail such notice, nor any defect in any notice so mailed,
to any particular Holder shall affect the sufficiency of such notice with respect to other Holders. 
 Section 7.3. Effect of
Headings. 
 The Article and Section headings herein are for convenience only and shall not affect the construction hereof. 
 Section 7.4. Successors and Assigns. 
 All covenants and agreements in this Agreement by Buyer shall bind its successors and assigns, whether so expressed or not. 
 Section 7.5. Benefits of Agreement. 
 Nothing in this Agreement, express or implied, shall give to any Person (other
than the parties hereto, the Holders and their permitted successors and assigns hereunder) any benefit or any legal or equitable right, remedy or claim under this Agreement or under any covenant or provision herein contained, all such covenants and
provisions being for the sole benefit of the parties hereto, the Holders and their permitted successors and assigns. The Holders shall have no rights or remedies hereunder except as expressly set forth herein. 
 Section 7.6. Governing Law. 
 This Agreement and the Real Estate CVRs shall be governed by and construed in accordance with the laws of the State of Delaware without regards to its rules of conflicts of laws. 
 Section 7.7. Legal Holidays. 
 In
the event that a Real Estate CVR Payment Date shall not be a Business Day, then, notwithstanding any provision of this Agreement to the contrary, any payment required to be made in respect of the Real Estate CVRs on such date need not be made on
such date, but may be made on the next succeeding Business Day with the same force and effect as if made on the Real Estate CVR Payment Date. 
  

 12 

 Section 7.8. Severability Clause. 
 In case any one or more of the provisions contained in this Agreement shall for any reason be held to be invalid, illegal or unenforceable in any respect,
such invalidity, illegality or unenforceability shall not affect any other provisions of this Agreement, but this Agreement shall be construed as if such invalid or illegal or unenforceable provision had never been contained herein. Upon such
determination that any term or other provision is invalid, illegal or unenforceable, the court or other tribunal making such determination is authorized and instructed to modify this Agreement so as to effect the original intent of the parties as
closely as possible so that the transactions and agreements contemplated herein are consummated as originally contemplated to the fullest extent possible. 
 Section 7.9. Counterparts. 
 This Agreement may be signed in any number of counterparts (which
may be effectively delivered by facsimile or other electronic means), each of which shall be deemed to constitute but one and the same instrument. 
 Section 7.10. Termination. 
 This Agreement shall terminate and be of no further force or effect, and the parties hereto
shall have no liability hereunder, upon the earliest to occur of (a) the payment of the last possible Real Estate CVR Payment Amount, (b) in the event that a Notice of Objection is not delivered within the Objection Period, the expiration
of the Objection Period or (c) in the event of the delivery of a Notice of Objection, either (i) the final determination in accordance with this Agreement that a Real Estate Sale was not closed on or before the CVR Outside Date or
(ii) the fulfillment of the last possible payment or other obligation required pursuant to a final determination made in accordance with this Agreement. 
 Section 7.11. Entire Agreement. 
 This Agreement and the Merger Agreement represent the entire
understanding of the parties hereto with reference to the Real Estate CVRs and this Agreement supersedes any and all other oral or written agreements made with respect to the Real Estate CVRs, except for the Merger Agreement. If and to the extent
that any provision of this Agreement is inconsistent or conflicts with the Merger Agreement, this Agreement shall govern and be controlling. 
 Section 7.12. Negotiation; Arbitration. 
 (a) Before any arbitration pursuant to Section 7.12(b), Buyer, the Rights
Agent and, if available, any Holder or Holders of at least 20% in the aggregate of the outstanding Real Estate CVRs shall negotiate in good faith for a period of 30 days to resolve any controversy or claim arising out of or relating to this
Agreement or the breach thereof. 
 (b) After expiration of the 30-day period contemplated by Section 7.12(a), such controversy or
claim, including any claims for breach of this Agreement, shall be settled by arbitration administered by the American Arbitration Association under its Commercial Arbitration Rules, and judgment on the award rendered by the arbitrators may be
entered in any court having jurisdiction thereof. Buyer, the Rights Agent and/or any Holder or Holders of at least 20% in the aggregate of the outstanding Real Estate CVRs 

  

 13 

 
may initiate an arbitration for any matter relating to this Agreement. However, in the event of a dispute arising from the delivery of a Notice of Objection,
the sole matter to be settled by arbitration shall be whether a Real Estate Sale has been closed on or before the CVR Outside Date. The number of arbitrators shall be three. Within 15 days after the commencement of arbitration, each party shall
select one person to act as arbitrator, and the two selected shall select a third arbitrator within 15 days of their appointment. If the arbitrators selected by the parties are unable or fail to agree upon the third arbitrator, the third arbitrator
shall be selected by the American Arbitration Association. The place of the arbitration shall be San Diego, California. The arbitrators shall be lawyers or retired judges with experience in the life sciences industry and with mergers and
acquisitions. Except as may be required by law, neither a party nor an arbitrator may disclose the existence, content or results of any arbitration hereunder without the prior written consent of both parties (provided that the Rights Agent may
disclose to the Holders any such information without the consent of Buyer). Any award payable in favor of the Holders or the Rights Agent as a result of arbitration shall be distributed to the Holders on a pro rata basis, based on the number of Real
Estate CVRs held by each Holder. Buyer shall pay all fees and expenses of the arbitration forum, including the costs and expenses billed by the arbitrators in connection with the performance of their duties described herein; provided, however, that
if the arbitrator rules in favor of Buyer, the Arbitrator’s fees and expenses shall be offset against the current or any future Real Estate CVR Payment Amount, if any, or any payment to be made thereafter under any of the other CVR Agreements.
Each party shall be responsible for its own attorney fees, expenses and costs of investigation. 
 [REMAINDER OF PAGE INTENTIONALLY LEFT
BLANK] 
  

 14 

 IN WITNESS WHEREOF, each of the parties has caused this Agreement to be executed on its behalf by
its duly authorized officers as of the day and year first above written. 
  

			
	LIGAND PHARMACEUTICALS INCORPORATED
		
	By:	 	  

	Name:	 	  

	Title:	 	  

	
	NEUROGEN CORPORATION
		
	By:	 	  

	Name:	 	  

	Title:	 	  

	
	[RIGHTS AGENT]
		
	By:	 	  

	Name:	 	  

	Title:	 	  

  

 15Form of Voting Agreement

 Exhibit 10.6 
 VOTING AGREEMENT 
 This VOTING AGREEMENT (this “Agreement”), is made and entered
into on and as of August     , 2009, by and between Ligand Pharmaceuticals Incorporated, a Delaware corporation (“Parent”), and the undersigned stockholder (“Stockholder”) of Neurogen
Corporation, a Delaware corporation (the “Company”). 
 RECITALS 
 A. Concurrently with the execution of this Agreement, Parent, Neon Signal, LLC, a Delaware limited liability company and a wholly owned subsidiary
of Parent (“Merger Sub”), and the Company are entering into an Agreement and Plan of Merger (the “Merger Agreement”), pursuant to which Merger Sub will be merged with and into the Company (the
“Merger”). Capitalized terms used but not defined herein shall have the meanings given to them in the Merger Agreement. 
 B. As of the date hereof, Stockholder is the direct, indirect and/or beneficial owner of certain shares of Company common stock as is indicated on the signature pages to this Agreement. 
 C. As a material inducement to enter into the Merger Agreement, Parent desires Stockholder to agree, and Stockholder is willing to agree, to vote
the Shares (as defined in Section 1.1 below), and such other shares of common stock of the Company over which Stockholder has voting power, on the terms and subject to the conditions set forth in this Agreement. 
 In consideration of the foregoing and the representations, warranties, covenants and agreements set forth in this Agreement, the parties agree as
follows: 
 1. Voting of Shares. 
 1.1 Shares. The term “Shares” shall mean all issued and outstanding Company Shares owned of record and/or beneficially owned (as defined in Rule 13d-3 under the Exchange Act of 1934, as
amended ( “Rule 13d-3”)) by Stockholder or over which Stockholder exercises sole voting power, in each case, as of the date of this Agreement; provided, however, Shares does not include any Company-issued options or warrants to
purchase or rights to subscribe for or otherwise acquire any securities of the Company (the “Options and Warrants”) owned of record and/or beneficially owned by Stockholder or over which Stockholder exercises voting power.
Stockholder agrees that any shares of common stock of the Company that Stockholder purchases or with respect to which Stockholder otherwise acquires beneficial ownership after the date of this Agreement and before the termination of this Agreement
pursuant to Section 5 below shall be subject to the terms and conditions of this Agreement to the same extent as if they constituted Shares as of the date hereof. 
 1.2 Agreement to Vote Shares. Stockholder hereby covenants and agrees that during the period commencing on the date hereof and continuing until
this Agreement terminates pursuant to Section 5 hereof, at any meeting (whether annual or special and whether or not an adjourned or postponed meeting) of the stockholders of the Company, however called, and in any action by written
consent of the stockholders of the Company, Stockholder shall appear at the meeting or otherwise cause any and all Shares to be counted as present thereat for purposes of establishing a quorum and vote (or cause to be voted) any and all Shares:
(i) in favor of the approval of the Merger and adoption of the Merger Agreement; (ii) against any Acquisition Proposal or Superior Proposal; and (iii) against any proposal or transaction which would reasonably be expected to prevent
or delay the consummation of the Merger or the Merger Agreement. Stockholder further agrees not to enter into any agreement or understanding with any person or entity the effect of which would be materially inconsistent with or violative of any
provision contained in this Section 1.2. Notwithstanding anything to the contrary contained herein, nothing in this Agreement shall be construed to limit or restrict the Stockholder or any designee, employee, representative or affiliate
of the Stockholder who is a director or officer of the Company or any subsidiary of the Company from acting in such person’s capacity as a director or officer of the Company or any subsidiary of the Company or voting in Stockholder’s sole
discretion on any matter other than those matters referred to in the first sentence of this Section 1.2. Stockholder hereby waives, and agrees not to assert or perfect, any dissenters’ rights or any similar rights that it may have
by virtue of ownership of the Shares. 

 1.3 Irrevocable Proxy. Concurrently with the execution of this Agreement, Stockholder agrees to
deliver to Parent a proxy in the form attached hereto as Exhibit A (the “Proxy”), which shall be irrevocable, with respect to the Shares, subject to the other terms of this Agreement. 
 1.4 Adjustments Upon Changes in Capitalization. In the event of any change in the number of issued and outstanding Company Shares by reason of any
stock split, reverse split, stock dividend (including any dividend or distribution of securities convertible into Company Shares), combination, reorganization, recapitalization or other like change, conversion or exchange of shares, or any other
change in the corporate or capital structure of the Company, the term “Shares” shall be deemed to refer to and include the Shares as well as all such stock dividends and distributions and any shares into which or for which any or
all of the Shares may be changed or exchanged. 
 2. Transfer and Other Restrictions. Stockholder represents, covenants and
agrees that, except for the proxy granted in Section 1.3 hereof and as contemplated by this Agreement: (i) Stockholder shall not, directly or indirectly, during the period commencing on the date hereof and continuing until this
Agreement terminates pursuant to Section 5 hereof, offer for sale or agree to sell, transfer, tender, assign, pledge, hypothecate or otherwise dispose of or enter into any contract, option or other arrangement or understanding with
respect to, or consent to, the offer for sale, sale, transfer, tender, pledge, hypothecation, encumbrance, assignment or other disposition of, or create any Encumbrance of any nature whatsoever with respect to, any or all of the Shares or any
interest therein; (ii) Stockholder shall not grant any proxy or power of attorney, or deposit any Shares into a voting trust or enter into a voting agreement or other arrangement, with respect to the voting of Shares (each a “Voting
Proxy”) except as provided by this Agreement; and (iii) Stockholder has not granted, entered into or otherwise created any Voting Proxy which is currently (or which will hereafter become) effective, and if any Voting Proxy has been
created, such Voting Proxy is hereby revoked. Notwithstanding the foregoing, Stockholder may transfer or otherwise dispose of any Shares (A) in open market resale transactions (e.g. in a transaction in which there have been no discussions,
agreements or understandings between the seller and the buyer or their respective agents or representatives and in connection with which no solicitation of buyers or offers to buy has occurred) with respect to resales of any Company Shares, and
(B) as a bona fide gift or gifts, provided that it shall be a condition to such transfer that each donee thereof executes and delivers to Parent (1) an agreement with Parent in the form of this Agreement and (2) an irrevocable proxy
in the form attached hereto as Exhibit A, in each case with respect to any and all Shares so transferred. 
 3. Representations and Warranties of Stockholder. Stockholder represents and warrants to Parent that: 
 3.1
Authority; Validity. Stockholder has all requisite capacity, power and authority to enter into this Agreement and to consummate the transactions contemplated hereby. The execution and delivery of this Agreement by Stockholder and the
consummation by Stockholder of the transactions contemplated hereby have been duly and validly authorized by all necessary action on the part of Stockholder. This Agreement has been duly executed and delivered by Stockholder. If this Agreement is
being executed in a representative or fiduciary capacity with respect to Stockholder, the person signing this Agreement has full power and authority to enter into and perform this Agreement. 
 3.2 Non-Contravention. The execution, delivery and performance of this Agreement does not, and the consummation of the transactions contemplated
hereby and compliance with the provisions hereof will not, contravene, conflict with, or result in any violation of, breach of or default by (with or without notice or lapse of time, or both) Stockholder under, or give rise to a right of
termination, cancellation or acceleration of any obligation under, or result in the creation of any Encumbrance upon any of the properties or assets of Stockholder under, any provision of (i) any loan or credit agreement, note, bond, mortgage,
indenture, lease or other agreement, instrument, permit, concession, franchise or license applicable to Stockholder or (ii) any judgment, order, decree, statute, law, ordinance, injunction, rule or regulation applicable to Stockholder or any of
Stockholder’s properties or assets, other than any such conflicts, violations, defaults, rights, or Encumbrances that, individually or in the aggregate, would not impair the ability of Stockholder to perform Stockholder’s obligations
hereunder or prevent, limit or restrict in any respect the consummation of any of the transactions contemplated hereby. There is no beneficiary or holder of a voting trust certificate or other interest of any trust of which 

  

 - 2 - 

 
Stockholder is settlor or trustee or any other person or entity, including any Governmental Entity, whose consent, approval, order or authorization is
required by or with respect to Stockholder for the execution, delivery and performance of this Agreement by Stockholder or the consummation by Stockholder of the transactions contemplated hereby. 
 3.3 Litigation. As of the date hereof, there is no action pending, or to the knowledge of Stockholder, threatened with respect to his ownership of
the Shares, nor is there any judgment, decree, injunction or order of any applicable Governmental Entity or arbitrator outstanding which would prevent the carrying out by Stockholder of his obligations under this Agreement or any of the transactions
contemplated hereby, declare unlawful the transactions contemplated hereby or cause such transactions to be rescinded. 
 3.4 Title.
As of the date hereof, Stockholder is the beneficial owner (as defined in Rule 13d-3) of the Shares of indicated on the signature pages hereto, which, on and as of the date hereof, are free and clear of any Encumbrances that, individually or in
the aggregate, would impair the ability of Stockholder to perform Stockholder’s obligations hereunder or prevent, limit or restrict in any respect the consummation of any of the transactions contemplated hereby. As of the date hereof, the
number of Shares, Options and Warrants set forth on the signature pages hereto are the only Shares or options or warrants to purchase or rights to subscribe for or otherwise acquire any securities of the Company owned of record or beneficially owned
(as defined in Rule 13d-3) by Stockholder or over which Stockholder exercises sole voting power and, except as set forth on such signature pages, Stockholder holds no options or warrants to purchase or rights to subscribe for or otherwise
acquire any securities of the Company and has no other interest in or voting rights with respect to any securities of the Company. 
 3.5
Power. Stockholder has sole voting power and sole power to issue instructions with respect to the matters set forth in Section 1 and Section 2 hereof and sole power to agree to all of the matters set forth in this
Agreement, in each case with respect to all of the Shares, with no limitations, qualifications or restrictions on such rights. 
 4. Representations and Warranties of Parent. Parent represents and warrants to Stockholder that: 
 4.1 Authority;
Validity. Parent has all requisite capacity, power and authority to enter into this Agreement and to consummate the transactions contemplated hereby. The execution and delivery of this Agreement by Parent and the consummation by Parent of the
transactions contemplated hereby have been duly and validly authorized by all necessary action on the part of Parent. This Agreement has been duly executed and delivered by Parent. If this Agreement is being executed in a representative or fiduciary
capacity with respect to Parent, the person signing this Agreement has full power and authority to enter into and perform this Agreement. 
 4.2 Non-Contravention. The execution, delivery and performance of this Agreement does not, and the consummation of the transactions contemplated hereby and compliance with the provisions hereof will not, (a) require Parent to
obtain the consent or approval or, or make any filing with or notification to, any governmental or regulatory authority, domestic or foreign, (b) require the consent or approval of any other person pursuant to any agreement, obligation or
instrument binding on Parent or its properties and assets, (c) conflict with or violate any organizational document or law, rule regulation, order, judgment or decree applicable to Parent or pursuant to which any of its or its
subsidiaries’ respective assets are bound or (d) violate any other material agreement to which Parent or any of its subsidiaries is a party. 
 5. Effectiveness; Termination; No Survival. This Agreement shall become effective upon its execution by Stockholder and Parent or upon the execution of the Merger Agreement by all parties thereto,
whichever is later. This Agreement may be terminated at any time by mutual written consent of Stockholder and Parent. This Agreement, and the obligations of Stockholder hereunder, including, without limitation, Stockholder’s obligations under
Section 1 and Section 2 above, shall automatically terminate, without any action by the parties hereto, upon the earlier to occur of the following: (i) such date and time as the Merger shall become effective in
accordance with the terms and provisions of the Merger Agreement; (ii) such date and time as the Merger Agreement shall have been validly terminated pursuant to Article VII thereof; or (iii) the date and time of any amendment,
modification, change or waiver, which waiver is made at the request of, or with the consent of, Parent, Merger Sub or their respective Representatives, to the terms 

  

 - 3 - 

 
of the Merger Agreement or one or more of the CVR Agreements executed after the date hereof that (a) is not consented to in writing by the Stockholder
in its sole discretion and (b) is or results in (w) any change (adverse-to-Stockholder) in the Exchange Ratio as defined in the Merger Agreement as of the date hereof, or (x) any change (adverse-to-Stockholder) to the economic terms
of the CVRs as set forth in the Merger Agreement and the forms of CVR Agreements attached thereto, as they exist on the date hereof, or (y) any change to the Merger Agreement provisions governing the economic terms of any potential cash payment
that may be paid to the Company’s stockholders (including Stockholder) before the Effective Time as permitted by Section 2.06(a)(iii) of the Merger Agreement, or (z) any change in the form of consideration payable pursuant to the
Merger Agreement or the CVR Agreements as in effect on the date hereof (provided that the addition of consideration in any form, without the reduction or elimination of any part of the full amount of each respective form of consideration as called
for in the Merger Agreement or the CVR Agreements as in effect on the date hereof, shall not be considered such a “change in the form of consideration”) (i.e., “exactly the same thing but with some more of the same too or with
something else extra too” shall not be considered such a “change in the form of consideration”). 
 6. Further
Assurances. Subject to the terms of this Agreement, from time to time, Stockholder shall execute and deliver such additional documents and use commercially reasonable efforts to take, or cause to be taken, all such further actions, and to do or
cause to be done, all things reasonably necessary, proper or advisable under applicable laws and regulations to consummate and make effective the transactions contemplated by this Agreement. 
 7. Miscellaneous. 
 7.1
Severability. If any term, provision, covenant or restriction of this Agreement is held by a court of competent jurisdiction to be invalid, void or unenforceable, the remainder of the terms, provisions, covenants and restrictions of this
Agreement shall remain in full force and effect and shall in no way be affected, impaired or invalidated. 
 7.2 Binding Effect and
Assignment. This Agreement and all of the provisions hereof shall be binding upon and inure to the benefit of the parties hereto and their respective successors and permitted assigns, but neither this Agreement nor any of the rights, interests
or obligations of the parties hereto may be assigned by either of the parties without the prior written consent of the other. 
 7.3
Amendments and Modification. This Agreement may not be modified, amended, altered or supplemented except upon the execution and delivery of a written agreement executed by the parties hereto. 
 7.4 Specific Performance; Injunctive Relief; Attorneys Fees. The parties hereto acknowledge that parties will be irreparably harmed and that there
will be no adequate remedy at law for a violation of any of the covenants or agreements of the other party set forth herein. Therefore, it is agreed that, in addition to any other remedies that may be available upon any such violation, each party
shall have the right to enforce such covenants and agreements by specific performance, injunctive relief or by any other means available to such party at law or in equity and each party hereby irrevocably and unconditionally waives any objection to
the other party seeking so to enforce such covenants and agreements by specific performance, injunctive relief and other means. If any action, suit or other proceeding (whether at law, in equity or otherwise) is instituted concerning or arising out
of this Agreement or any transaction contemplated hereunder, the prevailing party shall recover, in addition to any other remedy granted to such party therein, all such party’s costs and attorneys fees incurred in connection with the
prosecution or defense of such action, suit or other proceeding. 
 7.5 Notices. All notices and other communications hereunder shall
be in writing and shall be deemed given upon delivery either personally or by commercial delivery service, or sent via facsimile (receipt confirmed) to the parties at the addresses or facsimile numbers set forth on the signature page hereof (or at
such other address or facsimile numbers for a party as shall be specified by like notice). 
 7.6 Governing Law; Submission to
Jurisdiction. This Agreement shall be governed by and construed in accordance with the laws of the State of Delaware, regardless of the laws that might otherwise govern under applicable principles of conflicts of law thereof. The parties hereby
irrevocably and unconditionally consent to submit to the exclusive jurisdiction of the courts of the United 

  

 - 4 - 

 
States of America located in the State of Delaware (or, if such courts lack jurisdiction, the appropriate Delaware state courts) for any actions, suits or
proceedings arising out of or relating to this Agreement (and the parties agree not to commence any action, suit or proceeding relating thereto except in such courts), and further agree that service of any process, summons, notice or document by
U.S. certified mail shall be effective service of process for any action, suit or proceeding brought against the parties in any such court. The parties hereby irrevocably and unconditionally waive any objection to the laying of venue of any action,
suit or proceeding arising out of this Agreement in the courts of the United States of America located in the State of Delaware (or, if such courts lack jurisdiction, the appropriate Delaware state courts) and hereby further irrevocably and
unconditionally waive and agree not to plead or claim in any such court that any such action, suit or proceeding brought in any such court has been brought in an inconvenient forum. 
 7.7 Entire Agreement. The Merger Agreement, this Agreement and the Proxy granted hereunder constitute and contain the entire agreement and
understanding of the parties with respect to the subject matter hereof and supersede any and all prior negotiations, correspondence, agreements, understandings, duties or obligations between the parties respecting the subject matter hereof.

 7.8 Counterparts. This Agreement may be executed in counterparts, each of which shall be deemed an original, but all of which
together shall constitute one and the same instrument. 
 7.9 Captions. The captions to sections of this Agreement have been inserted
only for identification and reference purposes and shall not be used to construe or interpret this Agreement. 
 7.10 Stockholder
Capacity. Notwithstanding anything herein to the contrary, Stockholder makes no agreement or understanding herein in his capacity as a director or officer of the Company or any subsidiary of the Company, and the agreements set forth herein shall
in no way restrict Stockholder or any designee, employee, representative or affiliate of the Stockholder who is a director or officer of the Company or any subsidiary of the Company in the exercise of his fiduciary duties as a director or officer of
the Company or any subsidiary of the Company or limit or affect any actions taken by any designee, employee, representative or affiliate of the Stockholder who is a director or officer of the Company or Stockholder solely in his capacity as an
officer or director of the Company or any subsidiary of the Company. Stockholder has executed this Agreement solely in his capacity as the record and/or beneficial holder of Shares. 
 7.11 No Ownership Interest. Nothing contained in this Agreement shall be deemed to vest in Parent or Merger Sub any direct or indirect ownership
or incidence of ownership of or with respect to the Shares. All rights, ownership and economic benefits of and relating to such Shares shall remain vested in and belong to Stockholder or his affiliates, and Parent and Merger Sub shall have no
authority to direct Stockholder in the voting or disposition of any Shares, except as otherwise provided herein. 
 7.12 Option and
Warrant Exercises. Nothing in this Agreement shall require Stockholder to exercise any Option or Warrant. 
 [Signature Page Follows]

  

 - 5 - 

 IN WITNESS WHEREOF, the parties hereto have caused this Voting Agreement to be executed as of the date
first above written. 
  

							
	Ligand Pharmaceuticals Incorporated	 		 	  

		 		 		 	[STOCKHOLDER]
				
	By:	 	  
	 		 	
	Title:	 	  
	 		 	
				
		 		 		 	
				
	Address:	 		 		 	Address:
				
	Attn:	 		 		 	
	Fax:	 		 		 	Fax:
				
		 		 		 	Outstanding Company Shares beneficially owned by Stockholder:
				
		 		 		 	                                    
				
		 		 		 	Outstanding (Company-issued) Options and Warrants beneficially owned by Stockholder:
				
		 		 		 	                                    
				
		 		 		 	Other options, warrants or rights to purchase Company Shares beneficially owned by Stockholder:
				
		 		 		 	                                    

  

 - 6 - 

 EXHIBIT A 
 IRREVOCABLE PROXY 
 The undersigned stockholder (“Stockholder”) of Neurogen
Corporation, a Delaware corporation (the “Company”), hereby irrevocably appoints and constitutes John Higgins and Charles Berkman (collectively, the “Proxyholders”) the agents, attorneys-in-fact and proxies of the
undersigned, with full power of substitution and resubstitution, to the full extent of the undersigned’s rights with respect to all Shares (as defined in the Voting Agreement), including, without limitation, those Shares listed on the signature
page of that certain Voting Agreement of even date herewith between Ligand Pharmaceuticals Incorporated, a Delaware corporation (“Parent”) and Stockholder (the “Voting Agreement”), and any and all other Shares
acquired by Stockholder on or after the date hereof and before the date this proxy terminates, to vote the Shares as follows: the Proxyholders named above are empowered at any time before termination of this proxy to exercise all voting and other
rights (including, without limitation, the power to execute and deliver written consents with respect to the Shares) of the undersigned at every annual, special or adjourned meeting of the Company’s stockholders, and in every written consent in
lieu of any such meeting, or otherwise, (i) in favor of the approval of the merger of Neon Signal, LLC, a Delaware limited liability company and a wholly owned subsidiary of Parent (“Merger Sub”), with and into the Company
pursuant to that certain Agreement and Plan of Merger by and among Parent, Merger Sub and the Company (the “Merger Agreement”), and in favor of adoption of the Merger Agreement; (ii) against any Acquisition Proposal or Superior
Proposal (each as defined in the Merger Agreement); and (iii) against any proposal or transaction which would reasonably be expected to prevent or delay the consummation of the Merger or the Merger Agreement. 
 The Proxyholders may not exercise this proxy on any other matter. Stockholder may vote the Shares on all matters other than those set forth in the
immediately preceding paragraph. The proxy granted by Stockholder to the Proxyholders hereby is granted as of the date of this Irrevocable Proxy in order to secure the obligations of Stockholder set forth in Section 1.2 of the Voting
Agreement, and is irrevocable in accordance with subdivision (e) of Section 212 of the Delaware General Corporation Law. 
 This
proxy will automatically terminate upon the termination of the Voting Agreement in accordance with its terms. Upon the execution hereof, all prior proxies given by the undersigned with respect to the Shares and any and all other shares or securities
issued or issuable in respect thereof on or after the date hereof are hereby revoked and no subsequent proxies will be given until such time as this proxy shall be terminated in accordance with its terms. Any obligation of the undersigned hereunder
shall be binding upon the successors and assigns of the undersigned. The undersigned Stockholder authorizes the Proxyholders to file this proxy and any substitution or revocation of substitution with the Secretary of the Company and with any
Inspector of Election at any meeting of the stockholders of the Company. 
 This proxy is irrevocable and shall survive the insolvency,
incapacity, death, liquidation or dissolution of the undersigned. Nothing in this Proxy shall require a Stockholder to exercise any Option or Warrant or authorize the Proxyholders to exercise any Option or Warrant or take any other action with
respect to any Options or Warrants owned of record and/or beneficially owned by Stockholder or over which Stockholder exercises voting power. 
  

					
	 Dated: August     , 2009
	  	  
	  	
		  	[STOCKHOLDER]	  	

  

 - 7 -

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