Exhibit 10.1

AMENDMENT AND PATENT ASSIGNMENT AGREEMENT

This Amendment and Patent Assignment Agreement (this "Amendment"), dated as of this 2nd day of July, 2004 (the
"Amendment Date"), is made by and between Sepracor Inc., a Delaware corporation ("Sepracor"), and
Aventis Pharma SA (successor in interest to Rhone-Poulenc Rorer SA), a corporation organized under the laws of France ("Aventis").

RECITALS

A.    Sepracor
and Aventis entered into that certain License and Assignment Agreement dated as of September 30, 1999 (the "1999
Agreement").

B.    Aventis
owns certain patents and patent applications, if any, as more particularly described onSchedule 1.21, which are the
foreign counterparts of the RPR Application (as defined in the 1999 Agreement) assigned to Sepracor pursuant to the 1999 Agreement and certain know-how relating to (+) zopiclone, the
racemate or the other enantiomer thereof, or metabolites of any of the foregoing.

C.    Aventis
is willing to assign the above-referenced patents and patent applications, if any, to Sepracor and license to Sepracor exclusive rights under the above-referenced
know-how to make, have made, use, market, sell, offer for sale, have sold and distribute pharmaceutical products containing (+) zopiclone worldwide, on the terms and subject to the
conditions set forth in the 1999 Agreement and this Amendment, and Sepracor is willing to accept such assignment and license.

D.    Sepracor
is willing to allow Aventis to assign certain rights under the 1999 Agreement to a third party.

E.    Sepracor
and Aventis wish to amend certain provisions of the 1999 Agreement as set forth specifically in this Amendment.

NOW THEREFORE, in consideration of the mutual promises, covenants and agreements hereinafter set forth, the sufficiency of which is hereby
acknowledged, the parties to this Amendment mutually agree as follows:

ARTICLE 1

DEFINITIONS

Capitalized terms used herein and not otherwise defined shall have the meanings given to them in the 1999 Agreement, as amended.

ARTICLE 2

AMENDMENT OF 1999 AGREEMENT

Effective from and after the date hereof, subject to Article 5 of this Amendment, the 1999 Agreement shall be amended as follows:

2.1  All
references to the defined term "RPR" shall be replaced throughout the 1999 Agreement by the term "Aventis" as defined in this Amendment.

2.2  Article 1
(Definitions) is hereby amended as follows:



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2.3  The
existing Section 2.1 shall be made Section 2.1(a) and a new Section 2.1(b) is hereby added as follows:



2.4  Section 2.2
is hereby amended by adding the following phrase at the end of the first sentence:



2.5  Section 2.2
is hereby further amended by (i) adding the phrase "or, as of the Amendment Effective Date, the Additional Territory" after the term
"Territory" in the last sentence of Section 2.2

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and
(ii) replacing the phrase "Section 2.7" with the phrase "Section 2.9" in the first parenthetical in the first sentence of Section 2.2.

2.6  Section 2.3
is hereby amended by adding the phrase "or, as of the Amendment Effective Date, the Additional Territory" after the term "Territory" in the last line
of Section 2.3 and by deleting the word "European" in Section 2.3.

2.7  Section 2.7
is hereby deleted in its entirety.

2.8  A
new Section 2.9 is hereby added to the Agreement as follows:



2.9  Section 3.2.4
is hereby deleted in its entirety.

2.10  Section 5.2
is hereby amended by adding the phrase, "in the Territory" after the phrase "to avoid loss of any rights" in the first sentence of
Section 5.2.

2.11  Section 5.3
is hereby deleted in its entirety, and a new Section 5.3 is added in lieu thereof which reads in its entirety as follows:



2.12  Article 6
(Infringement) is hereby amended by adding the phrase "or the Additional Patents, as applicable" after the term "RPR Applications" each time such term
appears in Article 6.

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2.13  Article 8
(Term) is hereby deleted in its entirety, and a new Article 8 is added in lieu thereof which reads in its entirety as follows:



This Agreement will commence as of the Effective Date and, unless sooner terminated as provided hereunder, shall terminate on the expiration of the royalty
obligations of Article 3, after which time Sepracor will have a fully paid-up, royalty-free and irrevocable exclusive license under RPR Know-How and
Improvements to develop, have developed, make, have made, use, market, sell, offer for sale, have sold and distribute Product in the Territory and the Additional Territory. Notwithstanding the
foregoing, if Sepracor breaches its obligations under Section 2.4, then this Agreement shall terminate ten (10) years from the Effective Date, or thirty (30) days after Aventis
gives notice to Sepracor of such breach, as applicable. Upon any such early termination of this Agreement, all rights to RPR Know-How and Improvements licensed hereunder to Sepracor shall
revert to Aventis, and Sepracor and its Affiliates and Licensees shall make no further use of the same.

2.14  Section 10.1.5
is hereby amended by adding the following clause at the end of such Section 10.1.5:



2.15  Section 10.1.6
is hereby amended by adding the following clause at the end of such Section 10.1.6:



2.16  Section 10.1.7
is hereby amended by adding the following clause at the end of such Section 10.1.7:



2.17  Section 10.1.10
is hereby amended by adding the following clause at the end of such Section 10.1.10:



2.18  A
new Section 10.1.12 is hereby added as follows:



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2.19  Section 10.3
is hereby deleted in its entirety and hereby replaced with a new Section 10.3 as follows:



2.20  Article 11
(Adverse Events) is hereby amended and restated in its entirety as follows:



2.21  Section 12.1
is hereby amended by adding the phrase "or the Additional Territory" after the term "Territory" in Section 12.1.

2.22  Article 15
(Notices) is hereby amended by replacing the existing notice address for Aventis with the following address:



2.23  Section 23.2
is hereby amended by deleting the phrase "in the Territory," in the third line of Section 23.2.

2.24  A
new Article 26 is hereby added as follows:



From and after the Amendment Effective Date, Aventis shall ensure that Aventis and its Affiliates (and employees, consultants, and agents thereof) do not,
directly or indirectly, use or otherwise place in the public domain, any information owned by, or in the possession or control of (including without limitation information relating to Compound or any
metabolites thereof provided by Sepracor to Aventis or its Affiliates), Aventis or its Affiliates that is not in the public domain, specifically relating to Compound (to the extent such exists as of
the Amendment Date) or (±) zopiclone, or any metabolite of either, including but not limited to information relating to research, development, pharmacological
characteristics, clinical effect, clinical trials, manufacture, marketing, commercialization, distribution, importation, exportation, cost, pricing, supply, sales, sales support, or use thereof; provided,however, that in the Additional Territory, any current or future employees and agents of
Aventis or its Affiliates involved in research, development, manufacture, sales, marketing, promotion, medical communications, or regulatory maintenance of pharmaceutical products containing
(±) zopiclone in the Additional Territory, shall be free to use any Aventis information specifically relating to (±) zopiclone
solely in connection with those activities in the Additional Territory. For purposes of clarity, in no event shall the foregoing prohibit or in any way limit (i) the rights of Aventis or its
Affiliates to use, directly or

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indirectly,
such information in connection with any actual or proposed sale, assignment or other transfer of rights in (±) zopiclone from Aventis or its Affiliates to
a Third Party (a "Transferee") or (ii) the rights of any Transferee to use, directly or indirectly, such information. Notwithstanding anything to the contrary contained herein,
(i) Aventis, its Affiliates and any employee, agent, or consultant of Aventis, shall be allowed to use, directly or indirectly, such information as required by any applicable law or any
applicable regulatory authority or other governmental entity in the Additional Territory and (ii) the provisions of this Article 26 shall not exclude use of any information independently
developed by Sanofi-Synthelabo or its Affiliates prior to the Amendment Effective Date.

2.25  The
following schedules are hereby added as schedules to the 1999 Agreement:



2.26  Except
as otherwise set forth herein, the 1999 Agreement shall remain in full force and effect.

ARTICLE 3

ADDITIONAL OBLIGATIONS OF AVENTIS

3.1  Aventis
shall, within twenty (20) Business Days of the Amendment Effective Date, deliver copies of the documents described on Schedule 3.1 hereto to
Sepracor, to the extent Aventis has not previously delivered copies of such documents, solely to the extent such documents are within the possession or control of Aventis (or its Affiliates, agents,
employees or consultants) on the Amendment Date and are legally permitted to be disclosed.

3.2  Within
ten (10) Business Days after the Amendment Date, Aventis shall provide Sepracor with (i) a current docket listing and description of the status of
each of the Additional Patents and copies of all related outstanding actions, if any and (ii) a copy of the prosecution history of any pending applications among the Additional Patents, if any.
From and after the Amendment Date until the earlier of (x) the Amendment Effective Date and (y) the date, if any, that it is determined by Aventis and communicated to Sepracor that the
Amendment Effective Date will not occur, Aventis shall conduct maintenance and prosecution of the Additional Patents consistent with Aventis' past practice and otherwise in the ordinary course of
business,provided,however, that Aventis shall timely pay any taxes, annuities, or maintenance fees due
between the Amendment Date and the Amendment Effective Date.

ARTICLE 4

CONSENT TO ASSIGNMENT

4.1  Pursuant
to the terms of Section 18.1 of the 1999 Agreement, Sepracor hereby consents to the assignment by Aventis of Aventis' rights, in whole or in part, under
Article 3 and Article 4 of the 1999 Agreement, as amended by this Amendment, including, without limitation, its right to receive Royalties pursuant to Section 3.1, its right to
receive Royalty Statements pursuant to Section 4.1 and its right to conduct audits pursuant to Section 4.5.

4.2  In
connection with the foregoing consent to assignment, Aventis shall have the right to provide complete and unredacted copies of the 1999 Agreement and this Amendment
to any potential assignee, provided, however, that such potential assignee agrees to be bound by confidentiality provisions substantially similar to those set forth in Article 7 of the 1999
Agreement.

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ARTICLE 5

EFFECTIVE DATE

5.1  Except
with respect to the provisions of Sections 2.18, 2.22, 3.2 and 4.2 of this Amendment which shall be effective as of the Amendment Date, this Amendment shall
become effective on the date upon which the shareholders of Aventis SA shall have sold to Sanofi-Synthelabo, and Sanofi-Synthelabo shall have purchased from the shareholders of Aventis SA, more than
fifty percent (50%) of the shares and voting rights of Aventis SA in furtherance of the tender offer launched by Sanofi-Synthelabo with respect to Aventis SA on the terms set forth in the "Note
d'Information" that received approval of the French "Autorites des Marches Financiers", as the same may be amended (the "Purchase Event"). Notwithstanding the foregoing, to the extent an event occurs
which would require payment of $5,000,000 under Section 3.2.4 of the 1999 Agreement following the Amendment Date, but prior to the Amendment Effective Date, no such payment shall be made unless
it is determined by Aventis and communicated to Sepracor that the Amendment Effective Date will not occur (the date such notice is communicated, the "Termination
Date"), in which event such payment shall be made within (10) Business Days following the Termination Date.

[NO FURTHER TEXT ON THIS PAGE]

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IN WITNESS WHEREOF, the Parties have executed this Amendment as of the date first above written.

|AVENTIS PHARMA SA
|-----------------
|By:              
|Name:            
|Title:           
|SEPRACOR INC.    
|By:              
|Name:            
|Title:           

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SCHEDULE 1.21

ADDITIONAL PATENTS

|Country |  | Application Date |  | Application Number |  | Grant date |  | Patent Number |  | Expiration date
|------- |  | ---------------- |  | ------------------ |  | ---------- |  | ------------- |  | ---------------
|AR      |  | 16/01/1992       |  | 321649             |  | 31/05/1995 |  | 248024        |  | 31/05/2010     
|AT      |  | 16/01/1992       |  | 92903994.9-2101    |  | 12/04/1995 |  | E 121089      |  | 16/01/2012     
|AU      |  | 16/01/1992       |  | 92 12264           |  | 07/01/1997 |  | 671797        |  | 16/01/2012     
|BD      |  | 15/01/1992       |  | 92 5               |  | 14/01/1993 |  | 1002434       |  | 17/01/2007     
|BE      |  | 16/01/1992       |  | 92903994.9-2101    |  | 12/04/1995 |  | 609210        |  | 16/01/2012     
|BY      |  | 17/05/1994       |  | 1681               |  | 14/05/1997 |  | 1854          |  | 16/01/2012     
|CA      |  | 16/01/1992       |  | 2099782            |  | 03/12/2003 |  | 2099782       |  | 16/01/2012     
|CH      |  | 16/01/1992       |  | 92903994.9-2101    |  | 12/04/1995 |  | 609210        |  | 16/01/2012     
|CZ      |  | 16/01/1992       |  | 93 1380            |  | 02/04/1996 |  | 281011        |  | 16/01/2012     
|DE      |  | 16/01/1992       |  | 92903994.9-2101    |  | 12/04/1995 |  | 69202060.8    |  | 16/01/2012     
|DK      |  | 16/01/1992       |  | 92903994.9-2101    |  | 12/04/1995 |  | 609210        |  | 16/01/2012     
|ES      |  | 16/01/1992       |  | 92903994.9-2101    |  | 12/04/1995 |  | 2071486       |  | 16/01/2012     
|FI      |  | 16/01/1992       |  | 93 3248            |  | 14/11/1997 |  | 100331        |  | 16/01/2012     
|FR      |  | 16/01/1992       |  | 92903994.9-2101    |  | 12/04/1995 |  | 609210        |  | 16/01/2012     
|GB      |  | 16/01/1992       |  | 92903994.9-2101    |  | 12/04/1995 |  | 609210        |  | 16/01/2012     
|GR      |  | 16/01/1992       |  | 92903994.9-2101    |  | 12/04/1995 |  | 609210        |  | 16/01/2012     
|HU      |  | 16/01/1992       |  | P93 02063          |  | 02/10/2000 |  | 218928        |  | 16/01/2012     
|IE      |  | 16/01/1992       |  | 92 126             |  | 21/11/1995 |  | 66110         |  | 16/01/2012     
|IL      |  | 16/01/1992       |  | 100677             |  | 28/02/1996 |  | 100677        |  | 16/01/2012     
|IT      |  | 16/01/1992       |  | 92903994.9-2101    |  | 12/04/1995 |  | 609210        |  | 16/01/2012     
|LU      |  | 16/01/1992       |  | 92903994.9-2101    |  | 12/04/1995 |  | 609210        |  | 16/01/2012     
|MA      |  | 15/01/1992       |  | 22677              |  | 01/10/1992 |  | 22392         |  | 15/01/2012     
|MX      |  | 16/01/1992       |  | 92 180             |  | 12/08/1994 |  | 175679        |  | 16/01/2012     
|NG      |  | 16/01/1992       |  | 92 15              |  | 30/07/1992 |  | RP 11252      |  | 16/01/2012     
|NL      |  | 16/01/1992       |  | 92903994.9-2101    |  | 12/04/1995 |  | 609210        |  | 16/01/2012     
|NO      |  | 16/01/1992       |  | 93 1919            |  | 08/01/1997 |  | 179911        |  | 16/01/2012     
|NZ      |  | 15/01/1992       |  | 241313             |  | 20/07/1993 |  | 241313        |  | 15/01/2012     
|OA      |  | 16/01/1992       |  | 60387              |  | 15/04/1994 |  | 9807          |  | 16/01/2012     
|PH      |  | 16/01/1992       |  | 43784              |  | 23/12/1997 |  | 30982         |  | 23/12/2014     
|PK      |  | 16/01/1992       |  | 92 22              |  | 19/12/1993 |  | 132928        |  | 16/01/2008     
|PL      |  | 16/01/1992       |  | P 299834           |  | 01/02/1995 |  | 166976        |  | 16/01/2012     
|PT      |  | 16/01/1992       |  | 92903994.9-2101    |  | 12/04/1995 |  | 609210        |  | 16/01/2012     
|RU      |  | 16/01/1992       |  | 93 051787          |  | 10/05/1998 |  | 2110519       |  | 16/01/2012     
|SE      |  | 16/01/1992       |  | 92903994.9-2101    |  | 12/04/1995 |  | 609210        |  | 16/01/2012     
|SK      |  | 16/01/1992       |  | 93 719             |  | 18/02/1998 |  | 279060        |  | 16/01/2012     
|TN      |  | 17/01/1992       |  | 92 004             |  | 06/10/1992 |  | 16531         |  | 17/01/2012     
|YU      |  | 17/01/1992       |  | 92P 55             |  | 11/06/2002 |  | 48 878        |  | 17/01/2012     
|ZA      |  | 15/01/1992       |  | 92 302             |  | 28/10/1992 |  | 92 302        |  | 15/01/2012     

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SCHEDULE 2.1(b)

ASSIGNMENT OF ADDITIONAL PATENTS

ASSIGNMENT

WHEREAS,
Aventis Pharma SA ("Aventis"), a French corporation having a place of business at 20, avenue Raymond-Aron, F-92160 Antony, France, owns, by assignment, all right,
title, and interest in and to French Patent Application Serial No. 91-00490, entitled "Optically Active 5H-Pyrrolo[3,4-b] pyrazine Derivative,
Its Preparation and Pharmaceutical Compositions Containing Same", and PCT International Patent Application No. PCT/FR92/00031, and any and all non-United States patents or patent
applications related to either of the aforesaid applications, including without limitation the patents and patent applications listed in Attachment A, and any invention described therein (collectively
hereinafter "Eszopiclone Foreign Patents"); and

WHEREAS,
Sepracor Inc. ("Sepracor"), a Delaware corporation having a place of business at 84 Waterford Drive, Marlborough, Massachusetts USA 01752, is desirous of obtaining Aventis' entire
right, title, and interest in, to, and under the Eszopiclone Foreign Patents, and Aventis desires to assign to Sepracor its entire right, title and interest in the same.

NOW
THEREFORE, be it known that, for good and valuable consideration to Aventis, the receipt and sufficiency of which is hereby acknowledged, Aventis hereby sells, assigns, transfers, and sets over to
Sepracor, its lawful successors and assigns, Aventis' entire right, title, and interest in, to, and under Eszopiclone Foreign Patents (all of which are hereby incorporated by reference as if fully set
forth herein), any inventions described or claimed therein, all rights to claim priority on the basis of any Eszopiclone Foreign Patents, and all applications for Letters Patent that may be filed for
such invention in any country other than the United States and all Letters Patent that may be granted on any such application, and any and all extensions, supplemental protection certificates,
additions, divisions, substitutions, and renewals of any of the foregoing, in each case, as fully and entirely as the same would have been held and enjoyed by Aventis if this assignment had not been
made.

AND,
AVENTIS HEREBY further convenants that Aventis shall, from time to time after the date hereof upon the request of Sepracor, execute and deliver to Sepracor such further conveyance instruments or
confirmatory assignments as may be necessary or desirable to evidence more fully the transfer of ownership of all Eszopiclone Foreign Patents to Sepracor, or the original ownership of all the
Eszopiclone Foreign Patents on the part of Aventis, to the fullest extent possible, and to perform any other acts deemed necessary to carry out the intent of this instrument.

AND,
AVENTIS HEREBY authorizes and requests that any official of any country whose duty it is to issue patents or other evidence or forms of industrial property protection on applications as
aforesaid, to issue all patents or Letters Patents for this invention to Sepracor, its successors and assigns, in accordance with the terms of this instrument.

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IN
WITNESS WHEREOF, Aventis has caused its authorized representative to execute this Assignment

|AVENTIS PHARMA SA |  |  |  |      
|----------------- |  |  |  | -----
|By:               |  |  |  | Date:
|                  |  |  |  |      
|Name:             |  |  |  |      
|Title:            |  |  |  |      



|State of  |  | ) |  |     
|--------- |  | - |  | ----
|          |  | ) |  | SS.:
|County of |  | ) |  |     

On this            day
of                        , 2004, before me, a Notary Public in and for the State and County aforesaid, personally
appeared                        ,
to me known and known to me to be the person of that name, who signed and sealed the foregoing instrument, and he acknowledged the same to be his free act and deed.

| |  |                |  | ,
| |  | -------------- |  | -
| |  | Notary Public.

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ATTACHMENT A

|1.  |  | French Patent Application No. 91-00490, filed 17 January 1991;                 
|--- |  | -------------------------------------------------------------------------------
|2.  |  | PCT International Patent Application No. PCT/FR92/00031, filed 16 January 1992;
|3.  |  | European Patent Application No. 92903994.9-2101, filed 16 January 1992;        
|4.  |  | Argentinian Patent No. 248024, granted 31 May 1995;                            
|5.  |  | Austrian Patent No. E 121089, granted 12 April 1995;                           
|6.  |  | Australian Patent No. 671797, granted 7 January 1997;                          
|7.  |  | Bangladesh Patent No. 1002434, granted 14 January 1993;                        
|8.  |  | Belgian Patent No. 609210, granted 12 April 1995;                              
|9.  |  | Belarus Patent No. 1854, granted 14 May 1997;                                  
|10. |  | Canadian Patent No. 2,099,782, granted 3 December 2003;                        
|11. |  | Swiss Patent No. 609210, granted 12 April 1995;                                
|12. |  | Czech Republic Patent No. 281011, granted 2 April 1996;                        
|13. |  | German Patent No. 69202060.8, granted 12 April 1995;                           
|14. |  | Danish Patent No. 609210, granted 12 April 1995;                               
|15. |  | Spanish Patent No. 2071486, granted 12 April 1995;                             
|16. |  | Finnish Patent No. 100331, granted 14 November 1997;                           
|17. |  | French Patent No. 609210, granted 12 April 1995;                               
|18. |  | British Patent No. 609210, granted 12 April 1995;                              
|19. |  | Greek Patent No. 609210, granted 12 April 1995;                                
|20. |  | Hungarian Patent No. 218928, granted 2 October 2000;                           
|21. |  | Ireland Patent No. 66110, granted 21 November 1995;                            
|22. |  | Israeli Patent No. 100677, granted 28 February 1996;                           
|23. |  | Italian Patent No. 609210, granted 12 April 1995;                              
|24. |  | Japanese Patent Application No. 1992-504006, filed 16 January 1992;            
|25. |  | Luxembourg Patent No. 609210, granted 12 April 1995;                           
|26. |  | Moroccan Patent No. 22392, granted 1 October 1992;                             
|27. |  | Mexican Patent No. 175679, granted 12 August 1994;                             
|28. |  | Nigerian Patent No. RP 11252, granted 30 July 1992;                            
|29. |  | Netherlands Patent No. 609210, granted 12 April 1995;                          
|30. |  | Norwegian Patent No. 179911, granted 8 January 1997;                           
|31. |  | New Zealand Patent No. 241313, granted 20 July 1993;                           
|32. |  | OAPI Patent No. 9807, granted 15 April 1994;                                   
|33. |  | Philippine Patent No. 30982, granted 23 December 1997;                         
|34. |  | Pakistan Patent No. 132928, granted 19 December 1993;                          
|35. |  | Polish Patent No. 166976, granted 1 February 1995;                             
|36. |  | Portuguese Patent No. 609210, granted 12 April 1995;                           
|37. |  | Russian Federation Patent No. 2110519, granted 10 May 1998;                    
|38. |  | Swedish Patent No. 609210, granted 12 April 1995;                              
|39. |  | Slovakian Patent No. 279060, granted 18 February 1998;                         
|    |  |                                                                                

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|40. |  | Tunisian Patent No. 16531, granted 6 October 1992;       
|--- |  | ---------------------------------------------------------
|41. |  | Yugoslavian Patent No. 48 878, granted 11 June 2002; and 
|42. |  | South African Patent No. 92 302, granted 28 October 1992.

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SCHEDULE 3.1

ADDITIONAL DOCUMENTATION

Draft or completed reports of any clinical or nonclinical studies or experiments not published or previously provided to Sepracor as of the Amendment Effective
Date, including postmarketing reviews and safety surveillance reports relating to Compound, the racemate, the other enantiomer thereof, or metabolites of any of the foregoing.

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