SECURITIES AND EXCHANGE COMMISSION
		     	     Washington, D.C. 20549

			  	  SCHEDULE 13G
		       	      Rule 13d-1 and 13d-2
	    	    Under the Securities Exchange Act of 1934


		     	  	   Sepracor Inc.
		       		 (Name of Issuer)

			  	   Common Stock
		 	  (Title of Class of Securities)

			   	     817315104
			          (CUSIP Number)

			  	     7/24/2006
             (Date of Event which Requires Filing of this Statement)

Check the appropriate box to designate the rule pursuant to which this
Schedule is filed:

| | Rule 13d-1 (b)
|X| Rule 13d-1 (c)
| | Rule 13d-1 (d)

* The remainder of this cover page shall be filled out for a reporting
person's initial filing on this form with respect to the subject class of
securities, and for any subsequent amendment containing information which
would alter disclosures provided in a prior cover page.

The information required on the remainder of this cover page shall not be
deemed to be "filed" for the purpose of Section 18 of the Securities Exchange
Act of 1934 ("Act") or otherwise subject to the liabilities of that section of
the Act but shall be subject to all other provisions of the Act (however, see
the Notes).



 (1) Names and I.R.S. Identification Nos.(entities only) of reporting persons.

    Caxton International Limited

 (2) Check the appropriate box if a member of a group (see instructions)  (a)|_|
                                                                          (b)|_|

 (3) SEC use only.

 (4) Citizenship or place of organization.
    British Virgin Islands

Number of shares beneficially owned by each reporting person with:

 (5) Sole voting power:
    0

 (6) Shared voting power:
    6,093,394

 (7) Sole dispositive power:
    0

 (8) Shared dispositive power:
    6,093,394

 (9) Aggregate amount beneficially owned by each reporting person.
    6,093,394

 (10) Check if the aggregate amount in Row (9) excludes certain shares	|_|
    (see instructions).

 (11) Percent of class represented by amount in Row 9.
     5.6%

 (12) Type of reporting person (see instructions).
     CO

 (1) Names and I.R.S. Identification Nos.(entities only) of reporting persons.

     Caxton Associates, L.L.C.
     22-3430173

 (2) Check the appropriate box if a member of a group (see instructions)  (a)|_|
                                                                    	  (b)|_|

 (3) SEC use only.

 (4) Citizenship or place of organization.
    Delaware

    Number of shares beneficially owned by each reporting person with:
 (5) Sole voting power:
    0

 (6) Shared voting power:
    6,093,394

 (7) Sole dispositive power:
    0

 (8) Shared dispositive power:
    6,093,394

 (9) Aggregate amount beneficially owned by each reporting person.
    6,093,394

 (10)Check if the aggregate amount in Row (9) excludes certain shares	|_|
    (see instructions).

 (11)Percent of class represented by amount in Row 9.
    5.6%

 (12)Type of reporting person (see instructions).
    IA

 (1) Names and I.R.S. Identification Nos.(entities only) of reporting persons.
    Kovner, Bruce

 (2) Check the appropriate box if a member of a group (see instructions)  (a)|_|
                                                                          (b)|_|

 (3) SEC use only.

 (4) Citizenship or place of organization.
    United States

Number of shares beneficially owned by each reporting person with:
 (5) Sole voting power:
    0

 (6) Shared voting power:
    6,093,394

 (7) Sole dispositive power:
    0

 (8) Shared dispositive power:
    6,093,394

 (9) Aggregate amount beneficially owned by each reporting person.
    6,093,394

 (10) Check if the aggregate amount in Row (9) excludes certain shares	|_|
    (see instructions).

 (11) Percent of class represented by amount in Row 9.
     5.6%

 (12) Type of reporting person (see instructions).
     IN

Item 1(a). Name of Issuer:
           Sepracor Inc.

Item 1(b). Address of Issuer's Principal Executive Offices:
	   84 Waterford Drive
	   Marlborough, MA  01752

Item 2(a). Name of Person Filing:
(i)   Caxton International Limited ("Caxton International")
(ii)  Caxton Associates, L.L.C. ("Caxton Associates").  Caxton
      Associates is the trading advisor to Caxton International
      and as such, has voting and dispositive power with respect
      to its investments.
(iii) Mr. Bruce S. Kovner.  Mr. Kovner is the Chairman of Caxton
      Associates and the sole shareholder of Caxton Corporation,
      the manager and majority owner of Caxton Associates. As a
      result of the foregoing, Mr. Kovner may be deemed
      beneficially to own the securities of the Issuer owned
      by Caxton International.

Item 2(b). Address or Principal Business Office or, If None, Residence:
(i)   The address of Caxton International is c/o Prime Management
      Limited, Mechanics Building, 12 Church Street, Hamilton HM11,
      Bermuda.
(ii)  The address of Caxton Associates is Princeton Plaza, Building 2,
      731 Alexander Road, Princeton, NJ 08540.
(iii) The business address of Mr. Kovner is 500 Park Avenue,
      New York, NY  10022.

Item 2(c). Citizenship:
(i)   Caxton International is a British Virgin Islands corporation.
(ii)  Caxton Associates is a Delaware limited liability company.
(iii) Mr. Kovner is a United States citizen.

Item 2(d). Title of Class of Securities:
           Common Stock

Item 2(e). CUSIP No.:
           817315104

Item 3. If This Statement is Filed Pursuant to Rule 13d-1(b), or 13d-2(b) or
        (c), Check Whether the Person Filing is a:
           Not Applicable

If this statement is filed pursuant to Rule 13d-1(c), check this box. |X|

Item 4. Ownership

(a) Amount beneficially owned:
(i)   The amount of shares of Common Stock beneficially owned by
      Caxton International is 6,093,394.
(ii)  The amount of shares of Common Stock considered to be
      beneficially owned by Caxton Associates by reason of its
      voting and dispositive powers is 6,093,394.
(iii) Mr. Kovner, by reason of being Chairman of Caxton Associates
      and the sole shareholder of Caxton Corporation, the manager
      and majority owner of Caxton Associates, may also be deemed to
      beneficially own such shares.

(b) Percent of class:

(i)   Caxton International beneficially owns 5.6% of the Class
      of Common Stock.
(ii)  Caxton Associates is deemed to beneficially own 5.6%
      of the Class of Common Stock.
(iii) Mr. Kovner is deemed to beneficially own 5.6% of the Class
      of Common Stock.

(c) Number of shares as to which Caxton International has:
	(i)    Sole power to vote or to direct the vote:  0
	(ii)   Shared power to vote or to direct the vote:  6,093,394
	(iii)  Sole power to dispose or to direct the disposition:  0
	(iv)   Shared power to dispose or to direct the disposition
       	       of:  6,093,394

    Number of shares as to which Caxton Associates has:
	(i)    Sole power to vote or to direct the vote: 0
	(ii)   Shared power to vote or to direct the vote:  6,093,394
	(iii)  Sole power to dispose or to direct the disposition of:  0
	(iv)   Shared power to dispose or to direct the disposition
               of:  6,093,394

     Number of shares as to which Mr. Kovner has:
	(i)    Sole power to vote or to direct the vote: 0
	(ii)   Shared power to vote or to direct the vote:  6,093,394
	(iii)  Sole power to dispose or to direct the disposition of:   0
	(iv)   Shared power to dispose or to direct the disposition
               of:  6,093,394

Item 5. Ownership of 5 Percent or Less of a Class.

Not Applicable

Item 6. Ownership of More than 5 Percent on Behalf of Another Person.

Not Applicable

Item 7. Identification and Classification of the Subsidiary Which Acquired the
        Security Being Reported on by the Parent Holding Company or Control
        Person.

Not Applicable

Item 8. Identification and Classification of Members of the Group.

Not Applicable

Item 9. Notice of Dissolution of Group.

Not Applicable

Item 10. Certifications

By signing below I certify that, to the best of my knowledge and
belief, the securities referred to above were not acquired and are not
held for the purpose of or with the effect of changing or influencing
the control of the issuer of the securities and were not acquired and
are not held in connection with or as a participant in any transaction
having that purpose or effect.

After reasonable inquiry and to the best of my knowledge and belief, I certify
that the information set forth in this statement is true, complete and correct.

					Caxton International Limited

Date: 8/1/2006				/s/ Joseph Kelly
					Name: Joseph Kelly
					Title: Vice President and Treasurer


Date: 8/1/2006	 			/s/ Maxwell Quin
					Name: Maxwell Quin
					Title: Vice President and Secretary

					Caxton Associates, L.L.C.

Date: 8/1/2006	 			/s/ Scott B. Bernstein
					Name: Scott B. Bernstein
					Title: Secretary

Date: 8/1/2006				/s/ Bruce S. Kovner
					Name: Bruce S. Kovner
					Title: signed by Scott B. Bernstein
					       as Attorney-in-Fact


The original statement shall be signed by each person on whose behalf the
statement is filed or his authorized representative. If the statement is
signed on behalf of a person by his authorized representative other than
an executive officer or general partner of the filing person, evidence of
the representative's authority to sign on behalf of such person shall be
filed with the statement, provided, however, that a power of attorney for
this purpose which is already on file with the Commission may be
incorporated by reference.  The name and any title of each person who signs
the statement shall be typed or printed beneath his signature.

ATTENTION: Intentional misstatements or omissions of fact constitute Federal
criminal violations (see 18 U.S.C. 1001). (Secs. 3(b), 13(d)(1), 13(d)(2),
13(d)(5), 13(d)(6), 13(g)(1), 13(g)(2), 13(g)(5), 23, 48 Stat. 882, 894, 901;
sec. 203(a), 49 Stat. 704; sec. 8, 49 Stat. 1379; sec. 10, 78 Stat. 88a; sec.
2, 82 Stat. 454; secs. 1, 2, 84 Stat. 1497; secs. 3, 10, 18, 89 Stat. 97, 119,
155; secs. 202, 203, 91 Stat. 1494, 1498, 1499; (15 U.S.C. 78c(b), 78m(d)(1),
78m(d)(2), 78m(d)(5), 78m(d)(6), 78m(g)(1), 78m(g)(2), 78m(g)(5), 78w)) [43 FR
18499, Apr. 28, 1978, as amended at 43 FR 55756, Nov. 29, 1978; 44 FR 2148,
Jan. 9, 1979; 44 FR 11751, Mar. 2, 1979; 61 FR 49959, Sept. 24, 1996; 62 FR
35340, July 1, 1997; 63 FR 2867, Jan. 16, 1998; 63 FR 15287, Mar. 31, 1998]


Certification


The undersigned hereby certifies that the shares of Sepracor Inc. purchased
on behalf of Caxton International Limited were not acquired and are not being
held for the purpose of or with the effect of changing or influencing the
control of the issuer of such securities and were not acquired and are not
held in connection with or as a participant in any transaction having that
purpose or effect.



Date: 8/1/2006				/s/ Robert N. Wilson
					    Robert N. Wilson




                         JOINT ACQUISITION STATEMENT
                        PURSUANT TO RULE 13d-1(k) (1)

The undersigned acknowledge and agree that the foregoing statement on Schedule
13G is filed on behalf of each of the undersigned and that all subsequent
amendments to this statement on Schedule 13G shall be filed on behalf of each
of the undersigned without the necessity of filing additional joint acquisition
statements.  The undersigned acknowledge that each shall be responsible for the
timely filing of such amendments, and for the completeness and accuracy of the
information concerning him or it contained therein, but shall not be
responsible for the completeness and accuracy of the information concerning
the other, except to the extent that he or it knows or has reason to believe
that such information is inaccurate.

Dated: 8/1/2006

					Caxton International Limited

					/s/ Joseph Kelly
					Name: Joseph Kelly
					Title: Vice President and Treasurer

				  	/s/ Maxwell Quin
					Name: Maxwell Quin
					Title: Vice President and Secretary

					Caxton Associates, L.L.C.

				 	/s/ Scott B. Bernstein
					Name: Scott B. Bernstein
					Title: Secretary

				  	/s/ Bruce S. Kovner
					Name: Bruce S. Kovner
					Title: signed by Scott B. Bernstein
       					       as Attorney-in-Fact