Document:

<PAGE>
                                                                    Exhibit 4.1

                       AMENDMENT NO. 1 TO RIGHTS AGREEMENT

     THIS AMENDMENT NO. 1 (this "Amendment"), dated as of December 11, 2000, to
the Rights Agreement, dated as of November 17, 1998 (the "Rights Agreement"),
between Nanogen, Inc., a Delaware corporation (the "Company"), and FleetBoston,
N.A., as Rights Agent (the "Rights Agent"), is made with reference to the
following facts:

     A.   The Company and the Rights Agent have heretofore entered into the
Rights Agreement. Pursuant to Section 27 of the Rights Agreement, the Company
and the Rights Agent may, from time to time, supplement or amend the Rights
Agreement in accordance with the provisions of such Section.

     B.   The Board of Directors of the Company has determined that it is in the
best interests of the Company to amend the Rights Agreement such that, with
respect to the acquisition by Citigroup Inc. and its Affiliates and Associates
(as those terms are defined in the Rights Agreement) (collectively, "Citigroup")
of up to an aggregate of 25% of the shares of Common Stock of the Company,
Citigroup will not become an "Acquiring Person" and no "Stock Acquisition Date"
or "Distribution Date" (as such terms are defined in the Rights Agreement) will
occur, so long as Citigroup holds such shares solely as a Schedule 13G (or
successor form) filer ("13G-Filer") under the Securities Exchange Act of 1934.

     NOW, THEREFORE, in consideration of the foregoing and the mutual agreements
set forth herein, the parties hereto agree as follows:

     1.   The definition of "Acquiring Person" set forth in Section 1(a) of the
Rights Agreement is hereby amended in its entirety to read as follows:

          (a)  "Acquiring Person" shall mean any Person (as such term is
hereinafter defined) who or which, together with all Affiliates (as such term is
hereinafter defined) and Associates (as such term is hereinafter defined) of
such Person, shall be the Beneficial Owner (as such term is hereinafter defined)
of securities representing 15% or more of the shares of Common Stock then
outstanding or who or which was such a Beneficial Owner at any time after the
date hereof, whether or not such Person continues to be the Beneficial Owner of
securities representing 15% or more of the outstanding shares of Common Stock.
Notwithstanding the foregoing,

               (i)  in no event shall a Person who or which, together with all
Affiliates and Associates of such Person, is the Beneficial Owner of less than
15% of the Company's outstanding shares of Common Stock become an Acquiring
Person solely as a result of a reduction of the number of shares of outstanding
Common Stock, including repurchases of outstanding shares of Common Stock by the
Company, which reduction increases the percentage of outstanding shares of
Common Stock beneficially owned by such Person (provided that any subsequent
increase in the amount of Common Stock beneficially owned by such Person,
together with all Affiliates and

<PAGE>

Associates of such Person, without the prior approval of the Board of Directors
of the Company shall cause such Person to be an Acquiring Person);

               (ii) the term Acquiring Person shall not mean (A) the Company,
(B) any subsidiary of the Company (as such term is hereinafter defined), (C) any
employee benefit plan of the Company or any of its subsidiaries, (D) any entity
holding securities of the Company organized, appointed or established by the
Company or any of its subsidiaries for or pursuant to the terms of any such plan
or (E) Citigroup as a result of the acquisition by Citigroup of up to 25% of the
shares of Common Stock of the Company; provided, however, that the provisions of
this clause (E) shall remain in effect only so long as Citigroup retains its
status as a 13G Filer and; provided, further, if Citigroup inadvertently
acquires more than 25% of the shares of Common Stock of the Company and,
promptly after becoming aware of such fact, Citigroup divests a sufficient
number of shares of the Company's Common Stock so that Citicorp's beneficial
ownership no longer exceeds 25% of the shares of the Company's Common Stock,
than the provisions of this clause (E) shall remain in effect; and

               (iii) no Person shall be deemed to be an Acquiring Person if (A)
within five business days after such Person would otherwise have become an
Acquiring Person (but for the operation of this clause (iii)), such Person
notifies the Board of Directors that such Person did so inadvertently and within
two business days after such notification, such Person is the Beneficial Owner
of less than 15% of the outstanding shares of Common Stock, (B) by reason of
such Person's Beneficial Ownership of 15% or more of the outstanding shares of
Common Stock on the date hereof if prior to the Record Date, such Person
notifies the Board of Directors that such Person is no longer the Beneficial
Owner of 15% or more of the then outstanding shares of Common Stock or (C) if
the Board of Directors determines in good faith that a Person who would
otherwise be an "Acquiring Person," as defined pursuant to the foregoing
provisions of this paragraph (a), has become such inadvertently, and such Person
divests as promptly as practicable a sufficient number of shares of Common Stock
so that such Person would no longer be an "Acquiring Person," as defined
pursuant to the foregoing provisions of this paragraph (a).

     2.   The first sentence of Section 3(a) of the Rights Agreement is hereby
amended by adding the following to the end of such sentence:

     ; PROVIDED, HOWEVER, that in no event shall a Distribution Date be deemed
     to occur as a result of the acquisition by Citigroup of up to 25% of the
     shares of Common Stock of the Company, so long as Citigroup retains its
     status as a 13G Filer and, provided, further, that if Citigroup
     inadvertently acquires more than 25% of the shares of Common Stock of the
     Company and, promptly after becoming aware of such fact, Citicorp divests a
     sufficient number of shares of the Company's Common Stock so that
     Citicorp's beneficial ownership no longer exceeds 25% of the shares of the
     Company's Common Stock, than no Distribution Date shall be deemed to occur.

     3.   No "Stock Acquisition Date" shall be deemed to occur under the Rights
Agreement as a result of the acquisition by Citigroup of up to 25% of the shares
of Common Stock of the Company, so long as Citigroup retains its status as a 13G
Filer and, provided further, that if

                                     -2-
<PAGE>

Citigroup inadvertently acquires more than 25% of the shares of Common Stock of
the Company and, promptly after becoming aware of such fact, Citigroup divests a
sufficient number of shares of the Company's Common Stock so that Citigroup's
beneficial ownership of the Company's Common Stock no longer exceeds 25% of the
shares of the Company's Common Stock, than no Stock Acquisition Date shall be
deemed to occur under the Rights Agreement.

     4.   Section 26 of the Rights Agreement is hereby amended to substitute
"Equiserve Limited Partnership" for "Boston Equiserve Limited Partnership."

     5.   All amendments made to the Rights Agreement in this Amendment shall be
deemed to apply retroactively as well as prospectively.

     6.   This Amendment shall be governed by and construed in accordance with
the laws of the State of Delaware and for all purposes shall be governed by and
construed in accordance with all laws of such State applicable to contracts to
be made and performed entirely within such State.

     7.   This Amendment may be executed in counterparts, each of which shall be
an original, but such counterparts shall together constitute one and the same
instrument.

     IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be
duly executed and attested, all as of the date and year first above written.

Attest:                                       NANOGEN, INC.

By:   /s/ Kieran T. Gallahue                  By:  /s/ Howard C. Birndorf
      ------------------------                     -----------------------------
      Kieran T. Gallahue                           Howard C. Birndorf

Title: President and Chief                    Title: Chairman of the Board and
       Financial Officer                             Chief Executive Officer
       ------------------------                      ---------------------------

Attest:                                       FLEETBOSTON, N.A.

By:   /s/ Therese M. Collins                  By:  /s/ Katherine Anderson
      ------------------------                     -----------------------------

Title: Account Manager                        Title: Director of Client Services
       ------------------------                      ---------------------------

                                     -3-<PAGE>

                          PURCHASE AND SALE AGREEMENT
                          ---------------------------

      Vesper Park, LLC, a Massachusetts limited liability company (the
"Seller"), agrees to sell the Property (as hereinafter defined), and Sycamore
Networks, Inc., a Delaware corporation (the "Buyer"), agrees to buy the
Property, on the terms and subject to the conditions of this Agreement.

                                   ARTICLE I

                          Description of the Property
                          ---------------------------

1.1.  Property.  The "Property" shall consist of the land, together with the
      --------
improvements thereon, located in Tyngsborough, Middlesex County, Massachusetts,
shown as Lots 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16 and 17 and the Lot
entitled "Green Space `A'" on the plan (the "Plan") entitled "Definitive Plan,
Vesper Executive Park Subdivision of Land in Tyngsborough, Mass." dated December
11, 1987, revised March 1, 1988, prepared by Dana F. Perkins & Assoc., Inc.,
recorded in the Middlesex County Northern District Registry of Deeds (the
"Registry") in Plan Book 166 as Plan 53.

1.2.  Appurtenant Rights.  The Seller will convey the Property to Sycamore
      ------------------
together with the following (collectively, the "Appurtenant Rights and
Interests"):

      (a)  All of Seller's right, title and interest to those portions of the
           parcel or parcels of land entitled "Potash Hill Road" on the Plan
           beginning at the southeast portion of the parcel of land entitled
           "Temporary Turnaround (End of Phase I Roadway)" on the Plan and
           continuing in a counterclockwise direction through the Property to
           Westford Road (the "Discontinued Road");

      (c)  The right, appurtenant to the Property, to use all other portions of
           Potash Hill Road for all purposes for which roads and ways may be
           lawfully used in Town of Tyngsborough in common with Seller, its
           successors and assigns and others entitled thereto;

      (d)  The benefit, in common with others (including Seller and its
           successors and assigns) entitled to such benefits, of all easements,
           licenses, restrictions, reservations and other rights and interests
           of record that are appurtenant to the Property or said Potash Hill
           Road; and

      (d)  The benefit, in common with others (including Seller and its
           successors and assigns) entitled to such benefits, of all consents,
           variances, licenses, permits or other governmental authorizations and
           approvals affecting or relating to the Property and said Potash Hill
           Road, the benefits of which are transferable to the owner of the
           Property or to the owner of those portions of Potash Hill Road
           acquired by the Buyer or which may be transferred to the Buyer by
           their terms.
<PAGE>

                                  ARTICLE II

                           Payment of Purchase Price
                           -------------------------

2.1.  Purchase Price.  At the Closing (as hereinafter defined), the Buyer shall
      --------------
pay, subject to the provisions of Section 2.3 below, an amount (the "Purchase
Price") equal to $12,000,000.00, of which:

      (a)  $1,000,000.00 (the "Deposit") has been deposited with Goulston &
           Storrs, P.C. (the "Escrow Agent") to be held in escrow and disbursed
           in accordance with the terms and conditions of Section 2.2 of this
           Agreement and Exhibit A attached to this Agreement; and

      (b)  $11,000,000.00, subject to adjustments under Sections 2.3, 4.4 and
           4.5 of this Agreement (the "Closing Payment"), shall be paid to the
           Seller at the Closing by a wire transfer (written instructions for
           which the Seller shall provide to the Buyer at least three business
           days before the Closing) or a certified or bank check.

2.2.  Deposit.  (a) The Escrow Agent shall deposit the Deposit in an interest-
      -------
bearing money-market account, and the Buyer shall pay any income taxes on such
interest.  The provisions of Exhibit A, entitled "Escrow Agent Protective
Provisions" and attached to this Agreement, are incorporated into this
Agreement, and the Seller and the Buyer agree that the Escrow Agent shall have
the benefit of such provisions.  Without limiting the generality of the
immediately preceding sentence, in the event of any apparent conflict between
the duties of the Escrow Agent under the body of this Agreement and the
provisions of said Exhibit A, the provisions of said Exhibit A shall control.

      (b)  If (i) the Buyer exercises its right to terminate this Agreement
under Section 4.4 of this Agreement or (ii) at the Closing, the Buyer tenders
the Closing Payment but the Seller fails to perform its obligations set forth in
Sections 1.2 4.1, 4.2, 4.4 and 5.2 of this Agreement, then the Escrow Agent
shall return to the Buyer the Deposit and all accrued interest on the Deposit.
Subject to the terms and conditions of the immediately preceding sentence, if
the Buyer otherwise fails to purchase the Property for any reason (or no reason)
at the Closing, the Escrow Agent shall pay to the Seller the Deposit and all
accrued interest on the Deposit. Upon the acceptance and, as appropriate,
recordation of the Conveyance Documents (as defined in Section 5.2), the Escrow
Agent shall pay the Deposit to the Seller, and the Escrow Agent shall pay all
accrued interest on the Deposit to the Buyer. In the event of a dispute
concerning the disposition of the Deposit, the Escrow Agent shall dispose of the
Deposit only in accordance with (i) a written direction signed by both the
Seller and the Buyer or (ii) a final order of court of competent jurisdiction,
or (iii) as provided in Exhibit A attached to, and incorporated into, this
Agreement.

      (c)  The Seller shall pay any fees charged, and any reasonable out-of-
pocket expenses incurred, by the Escrow Agent in connection with the performance
of its duties

                                       2
<PAGE>

under this Section 2.2, except for any such expenses incurred in connection with
any such dispute concerning the disposition of the Deposit. In the event of any
such dispute, the Escrow Agent shall be reimbursed for its reasonable out-of-
pocket expenses incurred in connection with such dispute and any settlement of
such dispute either (i) as the Seller and the Buyer may mutually agree in
connection with any such settlement or (ii) in the event of the resolution of
such dispute by a final order, decree or judgment by a court of competent
jurisdiction, by the unsuccessful party in the legal action resulting in such
order, decree or judgment.

2.3.  Closing Adjustments.  The following adjustments to the Closing Payment
      -------------------
shall be made at the Closing:

      (a)  The Seller shall pay (i) any stamp, excise or other tax payable on
           the recording of the Deed (as hereinafter defined), (ii) all
           recording fees for any document, other than the Deed, recorded to
           render title to the Property in compliance with this Agreement, and
           (iii) any other expenses customarily paid by the Seller in a real
           estate transaction according to conveyancing practices in
           Massachusetts.

      (b)  The Buyer shall pay (i) the recording fees in connection with the
           recordation of the Deed and (ii) any other expenses customarily paid
           by the Buyer in a real estate transaction according to conveyancing
           practices in Massachusetts.

      (c)  The following charges shall be prorated between the Buyer and the
           Seller on a daily basis as of 12:01 a.m. on the date of the Closing:

           (i)    real estate taxes assessed or imposed with respect to the
                  Property for the then current fiscal tax year;

           (ii)   municipal assessments and betterments assessed after the date
                  of this Agreement;

           (iii)  such other charges as are customarily apportioned between
                  sellers and buyers of commercial real estate in Massachusetts.

2.4.  Real Estate Taxes.  If, at the Closing, the rate of real estate taxes, the
      -----------------
assessed valuation of the Property and/or the amount of any assessments or
betterments is not fixed for the then current fiscal tax year, real estate
taxes, assessments and betterments shall be apportioned upon the basis of the
rate, valuation or amount fixed for the then preceding fiscal tax year.  At the
request of the Buyer or the Seller within one year after the Closing, such
taxes, assessments and betterments shall be readjusted after the new rate or
valuation can be ascertained.  The provisions of this Section 2.4 shall survive
the delivery of the Deed.

                                  ARTICLE III

                    Seller's Representations and Warranties
                    ---------------------------------------

                                       3
<PAGE>

3.1   Litigation.  The Seller represents and warrant to the Buyer that, to the
      ----------
actual knowledge solely of Elkin McCallum, the Seller's Manager, without any
investigation of any kind, there is no action, suit or investigation pending or
threatened against the Property before any court or arbitrator or any
governmental body, agency or official.

3.2   Environmental Compliance.  The Seller represents and warrant to the Buyer
      ------------------------
that, except as set forth in the Level I Environmental Site Assessment of
Sanborn, Head & Associates dated July 22, 1998, to the actual knowledge solely
of Elkin McCallum, the Seller's Manager, without any investigation of any kind,
no notice, notification, demand, request for information, citation, summons or
other complaint has been served on, or delivered to, the Seller in writing by
any entity or individual, no penalty has been assessed, and no investigation or
review is pending or threatened by any governmental or other entity (i) claiming
any alleged violation by the Seller of any Environmental Law (as hereinafter
defined) applicable to the Property, (ii) claiming any alleged failure by Seller
to have any license, permit or other approval required under Environmental Laws
applicable to the Property or (iii) claiming any Release (as hereinafter
defined) in, upon or under the Property.  For the purpose of this Agreement, (x)
"Environmental Laws" means all laws, regulations, orders and judgments of any
governmental authority relating to the environment or to emissions, discharges
or releases of pollutants, contaminants, petroleum or petroleum products,
chemicals or industrial, toxic, radioactive or hazardous materials, substances
or wastes into the environment, including without limitation ambient air,
surface water, groundwater or land, or otherwise relating to the presence, use,
treatment, storage, manufacture, transportation, disposal or release of
pollutants, contaminants, petroleum or petroleum products, chemicals or
industrial, toxic, radioactive or hazardous materials, substances or wastes or
the clean-up or other remediation thereof; (y) "Release" means the treatment,
storage, recycling, transportation, disposal or release of Hazardous Substances;
and (z) "Hazardous Substances" means any asbestos and any substance containing
asbestos, polychlorinated biphenyls, petroleum and its derivatives and by-
products, explosives, radioactive materials, chemicals known to cause cancer or
reproductive toxicity and pollutants, effluents, contaminants, emissions and
other substances included in the definitions of hazardous or toxic wastes,
materials or substances under any Environmental Laws in such concentrations that
remediation or other response is required under Environmental Laws.

3.3   Survival. The provisions of this Article III shall survive the delivery of
      --------
the Deed.

                                  ARTICLE IV

                              Title and Condition
                              -------------------

4.1.  Condition of the Property.  At the Closing, the Seller shall deliver to
      -------------------------
the Buyer full possession of the Property, free of all tenants and occupants and
free of all personal property, refuse and Hazardous Substances which were not
present on or under the Property as of August 15, 2000.  By taking title at the
Closing, the Buyer acknowledges that this condition has been met and has no
further rights under this Section.

                                       4
<PAGE>

4.2.  Title.  At the Closing, Seller shall convey to the Buyer (or to a nominee
      -----
designated by written notice to the Seller at least three days before the
Closing), by a good and sufficient quitclaim deed (the "Deed"), good record and
marketable title to the Property and all of Seller's right, title and interest
in and to the Discontinued Road, free of (i) all Liens (as hereinafter defined)
and (ii) those Encumbrances (as hereinafter defined) which were not of record at
the Registry as of August 15, 2000.  For the purpose of this Agreement, (x)
"Liens" shall mean any attachments, lis pendens, options, mortgages, liens,
security interests, pledges and other monetary encumbrances (excluding liens for
real estate taxes for the then current fiscal tax year that are not due and
payable and liens for municipal betterments assessed after the date of this
Agreement), and (y) "Encumbrances" shall  mean any easements, rights-of-way,
restrictions of record at the Registry, covenants running with the land,
reservations of real property interests and other encumbrances of record at the
Registry, which, in Seller's reasonable judgment, will materially restrict or
interfere with the construction and development of buildings containing floor
area of 900,000 square feet and necessary associated driveways and roads,
facilities for parking, drainage, utilities and services, and other associated
improvements at the Property.  The Deed shall include (x) the conveyance by the
Seller to the Buyer of the Appurtenant Rights and Interests in accordance with
Section 1.2 of this Agreement and (y) a release and disclaimer by the Seller of
any right of the Seller to use the Discontinued Road.

4.3.  Buyer's Inspections.  Until the Closing, the Seller shall give the Buyer
      -------------------
and its employees, agents, attorneys, engineers, architects, contractors and
lenders full access to the Property.  The Buyer shall have the right to perform,
at its expense, such tests, inspections and surveys, including without
limitation soil, subsurface and groundwater tests, as the Buyer may determine
are necessary to evaluate the title and condition of the Property, its
compliance with laws and its suitability for development.

4.4.  Defects.  If, at the Closing, (a) the condition of the Property or the
      -------
Discontinued Road fails to conform to the requirements set forth in Section 4.1
of this Agreement, or (b) the title to the Property or the Discontinued Road
fails to conform to the requirements set forth in Section 4.2 of this Agreement,
then the Seller shall use reasonable efforts to make the condition of, and title
to, the Property and the Discontinued Road conform to such requirements
(provided, however, the Seller shall have no obligation to expend more than
$50,000, excluding monetary Liens, in connection with such reasonable efforts),
and the date of the Closing shall be postponed for a period of 30 days.  During
such period, in addition to, and not in limitation of, the Seller's obligations
under the immediately preceding sentence, the Buyer shall have the right to take
such actions on behalf of the Seller as are necessary to cure any failure of
title to the Property or the Discontinued Road to conform to such requirements,
and the Seller shall reimburse the Buyer, within ten days after written demand,
for any sums expended by the Buyer (including without limitation reasonable
attorneys fees) in its efforts to cure such non-conformity, up to but not
exceeding $50,000 (excluding monetary Liens).  If, at such postponed Closing,
the Seller has failed to reimburse the Buyer for any such sums, the Buyer shall
have the right to receive such reimbursement as a credit against the Purchase
Price.  If, at such postponed Closing, the condition of, or title to, the
Property or the Discontinued Road fail to conform to such requirements, the
Buyer may terminate this Agreement by written notice

                                       5
<PAGE>

to the Seller. The Buyer shall have the option, at either the original or
postponed Closing, to accept such condition of, or title to, the Property and
the Discontinued Road as the Seller can then deliver, in which case the Buyer
shall pay the Closing Payment to the Seller without deductions other than the
adjustments set forth in Sections 2.3 and 4.5 and this Section 4.4, and the
Seller shall deliver the Conveyance Documents to the Buyer. Nothing in this
Agreement shall give the Buyer the right to terminate this Agreement and obtain
the right to a return of the Deposit by reason of zoning, permits (other than
permits which are restrictions recorded at the Registry, covenants running with
the land or other encumbrances of record at the Registry) or other issues not
related to the title to the Property and the Discontinued Road. Without limiting
the generality of the immediately preceding sentence, conditions of the Property
affecting the cost of construction or permits and regulations and codes which
increase the cost of development, reduce the desired size of the development or
affect the siting of improvements on the Property do no constitute a basis for
the return of the Deposit under this Agreement or otherwise.

4.5.  Use of Purchase Price to Clear Title.  If any failure of the condition of,
      ------------------------------------
or title to, the Property or the Discontinued Road to conform to the
requirements of Section 4.2 can be cured by the payment of money to the holder
of any monetary Lien, the Buyer shall have the right, at either the original or
the postponed Closing, to cure such defect, and any amounts expended in such
cure shall be credited against the Purchase Price.

                                   ARTICLE V

                                    Closing
                                    -------

5.1.  Time and Place.  The consummation of the transactions contemplated in this
      --------------
Agreement (the "Closing") shall take place at 10:00 a.m. on October 30, 2000
(subject to any postponement under Section 4.4 of this Agreement), at the
offices of Testa, Hurwitz & Thibeault, LLP, 125 High Street, Boston,
Massachusetts, or at such other location as the Buyer shall designate by written
notice to the Seller.

5.2.  Conveyance Documents.  At the Closing, the Seller shall, at its expense,
      --------------------
deliver the following documents (the "Conveyance Documents"):

      (i)    The Deed, duly executed and acknowledged by the record owner(s) of
             the Property and the Discontinued Road and in recordable form (or
             in form appropriate for registration with respect to any registered
             land).

      (ii)   A good and sufficient release deed, duly executed and acknowledged
             by the record owner(s) of Lots 2 and 4 shown on the Plan and in
             recordable form (or in form appropriate for registration with
             respect to any registered land), conveying to the Buyer all of such
             record owners' right, title and interest in and to the Discontinued
             Road, including the release and disclaimer of any right of such
             record owners' to use the Discontinued Road.

                                       6
<PAGE>

      (iii)  If the record owner of the Property, the Discontinued Road or said
             Lots 2 or 4 (or the general partner of any such record owner which
             is a limited partnership) is a limited liability company, a
             certificate issued by the Secretary of State of The Commonwealth of
             Massachusetts evidencing the legal existence and good standing of
             such limited liability company and the identity of the Manager of
             such limited liability company or the person authorized to execute
             documents related to real property on behalf of such limited
             liability company, which Manager or person shall execute all
             Conveyance Documents on behalf of such limited liability company.

      (iv)   If the record owner of the Property, the Discontinued Road or said
             Lots 2 or 4 is a limited partnership, a certificate issued by the
             Secretary of State of The Commonwealth of Massachusetts evidencing
             the legal existence and good standing of such limited partnership
             and the identity of the general partner of such limited
             partnership, which general partner shall execute all Conveyance
             Documents on behalf of such limited partnership.

      (v)    Such other executed instruments of transfer and evidence of
             authority as the Buyer's title insurance company may reasonably
             require to convey to, and vest in, the Buyer title to (x) the
             Property and the Discontinued Road conforming to the requirements
             of Section 4.2 of this Agreement and (y) the other Appurtenant
             Rights and Interests in accordance with Section 1.2 of this
             Agreement.

      (vi)   An Affidavit of Non-Foreign Status under Section 1445 of the
             Internal Revenue Code, duly executed and acknowledged by the
             Seller.

      (vii)  An affidavit and indemnity, duly executed and acknowledged by the
             Seller, sufficient in form and substance to induce the Buyer's
             title insurance company to remove from Schedule B of the Buyer's
             title insurance policy the printed standard exceptions for (1)
             rights and claims of persons in possession of the Property and (2)
             liens for services, labor or materials furnished before the Closing
             not shown on the public records.

      (viii) A ground lease in the form attached to this Agreement as Exhibit B,
             duly executed by record owners of Lots 2 and 4 shown on the Plan.

      (ix)   A written amendment (the "Amendment") of the Reciprocal Easement
             Agreement dated November 28, 1998, between Vesper Park, LLC, a
             Massachusetts limited liability company, and Dutton Associates,
             Limited Partnership, a Delaware limited partnership, recorded with
             the Registry at Book 10288, Page 144 (the "Reciprocal Easement
             Agreement"), which amendment shall (i) be executed and acknowledged
             by record owners of the Property, the Discontinued Road and said
             Lots 2 and 4 shown on the Plan, (ii) be in recordable form, and
             (iii) amend the Reciprocal Easement Agreement to provide that (x)
             the term "Vesper Parcels", as used in the Reciprocal Easement
             Agreement, shall mean Lot 5 shown on the Plan only, (y) the

                                       7
<PAGE>

              term "Entire Premises" shall mean said Lots 2, 4 and 5 only, and
              (z) the term "common roadways" shall mean those portions of Potash
              Hill Road excluding the Discontinued Road.

      (viii)  A discharge of the Mortgage and Security Agreement from Francis D.
              Burke, Trustee of Vesper Properties, I Trust to Elkin McCallum,
              dated September 28, 1998 and recorded with the Registry at Book
              9589, Page 303, which discharge shall be executed and acknowledged
              by the holder of record of such Mortgage and Security Agreement
              and in recordable form.

      (ix)    An estoppel certificate, executed and acknowledged by the record
              owners of Lots 2 and 4 shown on the Plan and in recordable form,
              stating that the Reciprocal Easement Agreement is unmodified
              (except for the modifications made under the  Amendment) and in
              full force and effect and that, to the best of the knowledge of
              each such record owner, no "Owner" (as defined in the Reciprocal
              Easement Agreement") is in default in any respect under the
              Reciprocal Easement Agreement.

      (x)     Such other instruments as the Buyer or its counsel may reasonably
              request to consummate the transactions contemplated in this
              Agreement.

5.3.  Further Assurances.  After the Closing, the Seller shall execute or
      ------------------
provide any instruments reasonably requested by the Buyer, or on behalf of the
Buyer, and do or cause to be done all things necessary to consummate, confirm or
validate any transactions contemplated by this Agreement.  Without limiting the
generality of the immediately preceding sentence, the Seller shall use
reasonable efforts, before and after the Closing, to obtain from any holders of
mortgages encumbering any portion of Lot 2 or 4 shown on the Plan and from the
lessees under ground leases of any portion of said Lot 2 or 4 (i) a written
confirmation and acknowledgement, in recordable form, that such mortgagee and/or
lessee consents and agrees to the Amendment and (ii) a written release to the
Buyer or its nominee of all of such mortgagee's and/or lessee's right, title and
interest in and to the Discontinued Road, including the release and disclaimer
of any right of such mortgagee and/or lessee to use the Discontinued Road.  The
provisions of this Section 5.3 shall survive the delivery of the Deed.

                                  ARTICLE VI

                                   Defaults
                                   --------

6.1.  Buyer's Defaults.  Subject to the Buyer's right to terminate this
      ----------------
Agreement under Section 4.4 of this Agreement, if the Buyer fails to purchase
the Property for any reason (or no reason) at the Closing, the Seller shall have
the right to terminate this Agreement by written notice to the Buyer and retain
the Deposit as liquidated damages, which shall be the Seller's exclusive remedy
at law and in equity.  If the Seller so terminates this Agreement, the Buyer and
the Seller shall be released from all further obligations and liabilities under
this Agreement.

                                       8
<PAGE>

6.2.  Seller's Defaults.  If any of the Seller's representations or warranties
      -----------------
in this Agreement are incorrect or incomplete in any material respect, or if the
Seller fails to perform any of its obligations under this Agreement, the Seller
shall be in default, and the Buyer shall have the right to enforce any rights
and remedies it may have at law or in equity.

                                  ARTICLE VII

                                 Miscellaneous
                                 -------------

7.1.  Assignment.  The Buyer shall be entitled to assign this Agreement, in
      ----------
which event any such assignee shall replace and stand in the place of the Buyer
under this Agreement, and any such assignor shall thereafter have no further
obligation or liability under this Agreement.

7.2.  Time.  Time is of the essence of this Agreement.  Whenever in this
      ----
Agreement the expiration of a specified number of days or other period of time
gives rise to certain rights or obligations, if the expiration of the applicable
period falls on a Saturday, Sunday or legal holiday, such expiration shall
automatically be deemed extended to the next business day.

7.3.  Successors and Assigns.  This Agreement shall bind and inure to the
      ----------------------
benefit of the respective successors and assigns of the Buyer and the Seller.

7.4.  Entire Agreement.  This Agreement contains the entire agreement between
      ----------------
the Buyer and the Seller with respect to the transactions contemplated in this
Agreement and supersedes all prior negotiations, agreements and representations
between the Buyer and the Seller.  The Letter of Intent dated August 15, 2000,
between the Buyer and the Seller shall have no further force or effect.

7.5.  Counterparts.  This Agreement may be executed in any number of original
      ------------
counterparts, all of which evidence only one agreement, but only one of which
need be produced for any purpose.

7.6.  Modifications.  This Agreement may not be modified in any respect except
      -------------
by a written agreement executed by the Buyer and the Seller.  However, any
consent, waiver, approval or authorization shall be effective if signed by the
party granting or making such consent, waiver, approval or authorization.

7.7.  Notices.  Any notice, demand, consent, authorization or other
      -------
communication shall be effective only if in writing, signed by the party giving
such notice, demand, consent, authorization or communication, and delivered by
hand or sent by express delivery service or by registered or certified mail of
the United States Postal Service, return receipt requested, addressed to the
other party as follows:

If to the Buyer:                   Sycamore Networks, Inc.
                                   150 Apollo Drive
                                   Chelmsford, MA 01879

                                       9
<PAGE>

                                   Attention:  Mr. Peter Hamil

With a copy concurrently           Kevin M. McKenna, Esq.
delivered to:                      Testa, Hurwitz & Thibeault, LLP
                                   125 High Street
                                   Boston, MA  02110

If to the Seller:                  Vesper Park, LLC
                                   c/o Joan Fabrics Corporation
                                   100 Vesper Park
                                   Tyngsborough, MA 01879
                                   Attention:  Elkin McCallum

With a copy concurrently           Paul Buffum, Esq.
delivered to:                      c/o Joan Fabrics Corporation
                                   100 Vesper Park
                                   Tyngsborough, MA 01879

Either party may change its designated address or addressee by written notice to
the other party.  Unless otherwise specified, notices shall be deemed given on
the earlier to occur of (i) receipt, (ii) refusal of acceptance or (iii) the
third day after being mailed.

7.8.   Governing Law.  This Agreement shall be governed by, and construed and
       -------------
enforced in accordance with, the laws of The Commonwealth of Massachusetts.

7.9.   Severability.  The invalidation or unenforceability in any particular
       ------------
circumstances of any provision of this Agreement shall in no way affect any of
the other provisions of this Agreement, which shall remain in effect.

7.10.  No Partnership.  This Agreement shall not be construed as in any way
       --------------
establishing a partnership, joint venture, express or implied agency or
employer-employee relationship between the Buyer and the Seller.

7.11.  No Third-Party Beneficiaries.  This Agreement is for the sole benefit of
       ----------------------------
the Buyer and the Seller and their respective successors and permitted assigns,
and no other person or entity shall be entitled to rely on or receive any
benefit from this Agreement.

7.12.  No Waiver.  No express or implied consent to, or waiver of, a failure of
       ---------
any representation or warranty or a breach of any covenant shall be effective
unless in writing, and no such consent or waiver in one instance shall be
construed as a consent or waiver in any other instance or with respect to any
other representation, warranty or covenant.

7.13.  Remedies.  All of the rights and remedies under this Agreement and the
       --------
Conveyance Documents shall be distinct, separate and cumulative, and the
exercise of any such right or remedy shall not be in exclusion of, or a waiver
of, any other right or remedy.

                                       10
<PAGE>

7.14   Brokers. The Seller and the Buyer each represent and warrant to the other
       -------
that it has not dealt with any broker in connection with the purchase of the
Property by the Buyer, other than Taupier Real Estate, Inc. and Paul Johnson
Real Estate Partners.  The Seller shall pay any fee or commission due to Taupier
Real Estate, Inc., and the Buyer shall pay any fee or commission due to Paul
Johnson Real Estate Partners, in connection with the purchase of the Property by
the Buyer.

7.15   Merger.  The acceptance of the Deed and the other Conveyance Documents by
       ------
the Buyer or its nominee shall be deemed to be full performance and discharge of
every agreement and obligation under this Agreement, except for any obligations
under provisions of this Agreement which, by their express terms, survive the
delivery of the Deed.

                                       11
<PAGE>

The Buyer and the Seller execute this Agreement under seal as of October ____,
2000.

<TABLE>
<S>                                                    <C>
BUYER:                                                 SELLER:

SYCAMORE NETWORKS, INC.                                VESPER PARK, LLC

By:________________________________________            By:_________________________________________
Name:                                                  Name:  Elkin McCallum
Title: Chief Financial Officer and Vice                Title: Manager
       President of Administration and Finance
</TABLE>

                           Escrow Agent's Agreement
                           ------------------------

The Escrow Agent is a party to this Agreement only as to those provisions
relating to the Deposit, and, by executing this Agreement, the Escrow Agent
agrees to hold, disburse and apply the Deposit according to the terms of this
Agreement.

                                        Goulston & Storrs, P.C.

                                        By:______________________________
                                        Name:
                                        Title:

                                       12
<PAGE>

                                   Exhibit A
                                   ---------

                                 ESCROW AGENT
                             PROTECTIVE PROVISIONS

To induce Goulston & Storrs, P.C. (the "Escrow Agent") to act as the escrow
agent for the Deposit under the terms and conditions of Section 2.2 of this
Agreement, the Seller and the Buyer (together, the "Transaction Parties") and
the Escrow Agent hereby agree as follows:

1.   This Exhibit A and Section 2.2 of this Agreement (together, this "Escrow
     Agreement") set forth all of the Escrow Agent's duties with respect to
     escrow, release and disbursement of the Deposit.  The Escrow Agent shall
     not be obligated to take any action which it is not expressly required to
     take under this Escrow Agreement or which, in Escrow Agent's reasonable
     judgment, would subject it to any liability, cost or expense.

2.   In taking any action whatsoever hereunder, the Escrow Agent shall have the
     right, without incurring any responsibility or liability to any of the
     Transaction Parties therefor, to rely upon any notice or other document
     believed by the Escrow Agent to be genuine or to have been signed by a duly
     authorized person(s), or upon any evidence deemed by him to be sufficient,
     without making any investigation or determination as to the genuineness
     thereof, the truth or authority of any signatory thereon or the veracity of
     any such evidence.  The Escrow Agent may consult with counsel in connection
     with its duties hereunder and shall not be liable or responsible for any
     act taken, suffered or permitted on advice of such counsel.

3.   In the event of any dispute among the Transaction Parties regarding the
     release of the Deposit, or in the event the Escrow Agent receives
     conflicting demands or instructions with respect thereto, the Escrow Agent
     may, without any liability therefor, refuse to release the Deposit, or
     refuse to comply with such conflicting demands or instructions, until all
     such disputes and conflicts are resolved to the Escrow Agent's
     satisfaction.  Alternatively, in any such event, the Escrow Agent may
     deposit the Deposit with a court of competent jurisdiction in The
     Commonwealth of Massachusetts and commence an action (in the nature of
     interpleader or otherwise) joining all of the interested Transaction
     Parties to determine their rights with respect thereto, whereupon the
     Escrow Agent shall have no further obligations hereunder.  Each of the
     Transaction Parties hereby consents to the jurisdiction of any such court
     in connection with any such action.

4.   In the event that any of the Transaction Parties commences a legal action
     with respect to the Deposit, the Escrow Agent shall deposit the same with
     the court in which such suit has been brought, and thereupon the Escrow
     Agent shall have no further obligations hereunder.

5.   The Escrow Agent may resign and be discharged of its duties hereunder by
     giving thirty (30) days written notice of its desire to do so to each of
     the Transaction Parties.  In such

                                       13
<PAGE>

     event, the Transaction Parties shall, within thirty (30) days after the
     date of the Escrow Agent's resignation notice, furnish the Escrow Agent
     with written instructions for the release of the Deposit to a successor
     escrow agent; and if the Escrow Agent shall not have received such written
     instructions within such thirty (30) day period, the Escrow Agent may
     petition any court of competent jurisdiction in The Commonwealth of
     Massachusetts for the appointment of a successor escrow agent, and, upon
     such appointment, the Escrow Agent shall deliver the Deposit to such
     successor and shall have no further obligations hereunder.

6.   The Escrow Agent shall not be liable or responsible for any action or
     failure to act in connection with this Escrow Agreement or any consequence
     thereof (including, without limitation, loss of the Deposit) unless such
     action or failure to act shall be held to constitute gross negligence or
     intentional misconduct on the part of the Escrow Agent.

7.   The Transaction Parties hereby jointly and severally agree to defend,
     indemnify and hold harmless the Escrow Agent from and against any and all
     claims, damages, losses, costs, expenses and liability of every kind
     (including, without limitation, reasonable attorneys' fees) to which the
     Escrow Agent may be subjected or put arising out of or in connection with
     this Escrow Agreement (including, without limitation, judgments, damages,
     costs and expenses incurred in connection with any action or proceeding
     brought by or against Escrow Agent) except for any claims, damages, losses,
     costs, expenses and liability which shall have been judicially determined,
     finally and with no further right of appeal, to have been caused by the
     gross negligence or intentional misconduct of Escrow Agent.

                                       14
<PAGE>

                                   Exhibit B
                                   ---------

                                 GROUND LEASE

[INSERT NAME OF OWNER OF LOT 5], a ____________________ with an address at 10
Elizabeth Drive, Chelmsford, Massachusetts 01824-4111 ("Landlord"), and
___________________ [INSERT NAME(S) OF OWNER(S) OF LOTS 2 AND 4], a
___________________ ("Tenant") with an address at 100 Vesper Executive Park,
Tyngsboro, Massachusetts 01879, enter into this Ground Lease (this "Lease") as
of ______________, 2000.

                             Preliminary Statement
                             ---------------------

     Landlord has accepted a deed for the land, together with the improvements
thereon, located in Tyngsborough, Middlesex County, Massachusetts, shown as Lot
5 ("Lot 5") on the plan (the "Plan") entitled "Definitive Plan, Vesper Executive
Park Subdivision of Land in Tyngsborough, Mass." dated December 11, 1987,
revised March 1, 1988, prepared by Dana F. Perkins & Assoc., Inc., recorded in
the Middlesex North Registry of Deeds in Plan Book 166 as Plan 53.  Tenant is
the owner of the land, buildings and other improvements commonly known as ___
and ___ Potash Hill Road [INSERT STREET ADDRESS], Tyngsborough, Massachusetts,
shown as Lots 2 and 4 on said Plan (together, Lots 2 and 4").

     Landlord wishes to lease to Tenant, on the terms and conditions of this
Lease, (i) the structure located on Lot 5 as of the date of this Lease which
contains equipment for pumping water (the "Pump House"),  (ii) a parcel of land
which includes the land on which the Pump House is situated and which extends
ten feet in all directions from the outside surface of the exterior walls of the
Pump House (the "Leased Land"), and such pumps, pipes, mains, conduits, manholes
and other equipment and fixtures associated with the pumping of water through
the Pump House to the buildings and other improvements on Lots 2 and 4 as are
located on or under Lot 5 as of the date of this Lease (collectively, the
"Pumping Equipment"; together with the Pump House and the Leased Land, the
"Leased Premises").  Tenant wishes to accept a lease of the Leased Premises on
the terms and conditions of this Lease.

                                   Agreement
                                   ---------

     In consideration of the mutual covenants in this Lease and for other
valuable consideration, the receipt and sufficiency of which Landlord and Tenant
hereby acknowledge, Landlord hereby leases to Tenant all of Landlord's rights,
title and interests, if any, in and to the Leased Premises, and Tenant hereby
accepts such lease from Landlord, on the following terms and conditions:

     1.   Appurtenant Rights.  Tenant shall have the right, appurtenant to the
          ------------------
Leased Premises, to enter the existing driveway on Lot 5 for the purpose of
access to the Leased Premises.

                                       15
<PAGE>

     2.   Term.  The term of this Lease shall be 99 years, commencing on the
          ----
date of this Lease and ending on the day before the ninety-ninth anniversary of
such date (the "Term").

     3.   Rent.  Tenant shall pay to Landlord rent at a rate of one dollar
          ----
($1.00) per year of the Term, which rent shall pay to Landlord in one lump sum
at the time of the execution of this Lease.

     4.   Taxes.  Tenant shall pay to Landlord all real estate taxes,
          -----
assessments and betterments levied on, or assessed against, the Leased Premises
by any governmental authority with respect to any fiscal tax year, or portion of
a fiscal tax year, included in the Term ("Taxes").  If any such governmental
authority assesses the Pump House, Pumping Equipment or the Leased Land
separately from the remainder of Lot 5, Tenant shall pay, on account of Taxes,
the entire amount of such separate assessment.  If any such governmental
authority does not assess the Leased Land separately from the remainder of Lot
5, Tenant shall pay, on account of Taxes, a fraction of real estate taxes,
assessments and betterments levied on, or assessed against Lot 5 by such
governmental authority, the numerator of which fraction shall be the area of the
Leased Land and the denominator of which fraction shall be the area of Lot 5.
Tenant shall not be responsible for paying any real estate taxes, assessments or
betterments levied on, or assessed against, any buildings or other improvements
on Lot 5 other than the Pump House and Pumping Equipment.  If the Term includes
only a portion of any fiscal tax year, the Taxes for such fiscal tax year shall
be prorated based on the fraction of such fiscal tax year that falls within the
Term.  Tenant shall make such payments to Landlord, as additional rent, within
30 days after receiving a written invoice stating the amount of such real estate
taxes, assessments or betterments.

     5.   Repairs and Maintenance.  Tenant accepts the Leased Premises in its
          -----------------------
condition as of the date of this Lease, without any express or implied
representation or warranty, except as specified in this Lease.  Tenant, at its
sole expense, either (i) shall perform any repairs, replacements or maintenance
necessary to maintain the Leased Premises in good condition and working order
and in compliance with all applicable laws or (ii) shall remove the Pump House
from the Leased Premises.  Tenant's right to remove the Pump House and the
Pumping Equipment shall be subject to the Reciprocal Easement Agreement (as
hereinafter defined), but, if Tenant removes the Pump House, Tenant shall, at
Landlord's request, remove all of the Pumping Equipment, including any Pumping
Equipment located underground.  Tenant, at its sole expense, shall restore the
surface of Lot 5 to its original condition after performing any such repairs,
replacements or maintenance or any such removal, and Tenant shall securely cap
or close off all abandoned or inactive Pumping Equipment that Landlord permits
to remain on Lot 5.  If Tenant fails to perform any repairs, replacements,
maintenance or removal which Tenant is required to perform under this Section 5,
and if such failure continues for more than 30 days after Tenant receives
written notice of such failure, then Landlord shall have the right, but not the
obligation, to enter the Leased Premises and perform any such repairs,
replacements, maintenance or removal at Tenant's expense, and Tenant shall
reimburse Landlord for any costs and expenses incurred by Landlord in connection
with performing such repairs, replacements, maintenance or removal, within ten
days after receiving a written invoice stating the amount of such costs and
expenses; provided, however, Landlord shall not remove the Pump House without
Tenant's prior written

                                       16
<PAGE>

consent, and Landlord shall not remove the Pumping Equipment without Tenant's
prior written consent unless Tenant has previously removed the Pump House.

     6.   Use.  Tenant shall use the Leased Property only for the purpose of
          ---
pumping water (and maintaining water pressure) through the Pump House to Lots 2
and 4 (the "Permitted Use") in compliance with all applicable laws.  Tenant
shall not use the Leased Property or permit the use of the Leased Premises in
any manner that constitutes a nuisance.  Tenant shall not, nor shall Tenant
permit its employees, agents, contractors, invitees, successors or assigns to,
produce, generate, keep, maintain, use, store, release or dispose of (into the
sewage or waste disposal system or otherwise) any substance which is or may
hereafter be classified as a hazardous or toxic wastes, materials or substances
under any federal, state or local laws, rules and regulations, including without
limitation 42 U.S.C. Section 6901 et seq., 42 U.S.C. Section 9601 et seq., 42
U.S.C. Section 2601 et seq., 49 U.S.C. Section 1802 et seq. and Massachusetts
General Laws, Chapter 21E and the rules and regulation promulgated thereunder,
as such laws, rules and regulations may be amended from time to time
(collectively, "Environmental Laws"), in, on, at, under, within or from the
Leased Premises or Lot 5, except for de minimis amounts of such substances as
are customarily used in connection with the use, operation, maintenance and
repair of the Pump House and Pumping Equipment for the Permitted Use, and then
only in compliance with all applicable Environmental Laws.  Tenant shall
immediately notify Landlord of any incident in, on or about the Leased Premises
of which Tenant becomes aware that would require the filing of a notice under
any Environmental Laws.

     7.   Access.  Landlord shall have the right to enter upon the Leased Land
          ------
at any time and to enter the Pump House upon reasonable advance notice to
Tenant, except in an emergency, for the purpose of inspecting the Pump House and
the Pumping Equipment and performing any repairs to, or any replacements,
maintenance or removal of, the Pump House or Pumping Equipment which Landlord is
permitted to do under this Lease.

     8.   Indemnity and Waiver. Tenant shall indemnify and hold harmless
          --------------------
Landlord, its successors and assigns, its mortgagees and any other persons or
business organizations holding title to or any interest in any portion of Lot 5
from time to time, and their respective directors, officers, trustees, managers,
members and employees (collectively, "Indemnified Parties") from all claims,
liabilities, damages, losses, costs and expenses arising out of (i) the use,
operation, inspection, repair, replacement, maintenance or removal of the Pump
House or the Pumping Equipment, (ii) the presence and activities of Tenant's
agents, employees, contractors or invitees on the Leased Land or any other
portion of Lot 5, (iii) the negligence or willful misconduct of the Tenant or
its agents, employees, contractors or invitees on or about Lot 5, or (iv) any
default by Tenant in the payment or performance of its obligations under this
Lease, except to the extent such claims, liabilities, damages, losses, costs or
expenses arise out of the negligence or willful misconduct of the Indemnified
Parties. Landlord shall not be liable to Tenant for any claim, liability,
damage, loss, cost or expense, whether or not caused by the negligence of
Landlord or any Indemnified Party, to the extent that such claim, liability,
damage, loss, cost or expense is covered under any insurance carried by Tenant
or would have been covered under any insurance which Tenant is required to carry
under Section 9 of this Lease.

                                       17
<PAGE>

     9.   Insurance.  During the Term, Tenant, at its sole expense, shall obtain
          ---------
and carry:

     (i) a policy of commercial general liability insurance, in an amount not
     less than $2,000,000.00 per occurrence (or such greater reasonable amount
     as may be required by Landlord's mortgagees or as may be carried by prudent
     owners of property used for offices and research and development from time
     to time, provided that Landlord has given written notice of such greater
     amount to Tenant), for claims based on bodily injury (including death),
     personal injury and property damage relating to the Premises (including
     without limitation coverage for all claims, liabilities, damages, losses,
     costs and expenses for bodily injury, death, personal injury and property
     damage against which Tenant is required to indemnify and hold harmless the
     Indemnified Parties under Section 8 of this Lease), naming as additional
     insureds Landlord and the holder(s) of any mortgage, and the lessor under
     any ground lease, of Lot 5 or any portion of, or interest in, Lot 5; and

     (ii) a policy of insurance covering the Pump House and Pumping Equipment
     for all direct risk of physical loss, on an occurrence basis, in an amount
     and value not less than their full replacement cost, which policy shall
     provide, by its terms or under an endorsement, a waiver by the insurer of
     any rights of subrogation against the Indemnified Parties.

Any such policies shall be written by an insurer qualified to do business and in
good standing in Massachusetts and shall provide that it shall not be canceled
or amended in any manner that reduces the coverage afforded to Landlord without
written notice to Landlord at least 30 days in advance.  Upon request, Tenant
shall each promptly deliver to Landlord certificates evidencing such policies.

     10.  Eminent Domain.  In the event of any permanent appropriation of all or
          --------------
any portion of the Leased Premises by eminent domain or a permanent condemnation
of all or any portion of the Leased Premises for any public or quasi-public use,
this Lease shall terminate as of the date of such appropriation or condemnation.
Landlord expressly reserves, and Tenant hereby assigns to Landlord, all rights
to any award or compensation relating to any such appropriation or condemnation
except any award or compensation for damage to the Pump House or Pumping
Equipment.

     11.  Assignments and Subleases.  Tenant shall sublet all or any portion of
          -------------------------
the Leased Premises without in each instance obtaining Landlord's prior written
consent, which consent Landlord may withhold or condition in its sole
discretion.  Tenant shall not assign this Lease, including without limitation an
assignment by operation of law and any mortgage or pledge of any interest in
this Lease, without in each instance obtaining Landlord's prior written consent,
which consent Landlord may withhold or conditioned in its sole discretion;
provided, however, that Tenant may assign this Lease, without Landlord's
consent, to the transferee or mortgagee in connection with the transfer or
mortgage of fee simple title to either or both of Lots 2 and 4 (an "Appurtenant
Transfer").  If Tenant transfers fee simple title to either or both of Lots 2
and 4, Tenant shall assign its rights, title and interest in and to this Lease
to such transferee.  In the event of any such conveyance or mortgage of fee
simple title to one, but not both, of Lots 2 and 4, the grantee of such
conveyance or the mortgagee holding such mortgage, as the case may be, shall

                                       18
<PAGE>

hold its rights, title and interests under this Lease in common with the person
or business organization holding fee simple title to the other such lot.  Any
such assignment or sublease without Landlord's prior written consent (except in
connection with an Appurtenant Transfer) shall be void.

     12.  Joint and Several Obligations.  If at any time more than one person or
          -----------------------------
business organization holds the rights, title and interest of Tenant under this
Lease, the obligations of such persons or business organizations under this
Lease shall be joint and several.

     13.  Default.  If Tenant fails to pay or perform its obligations under this
          -------
Lease and such failure continues for more than 60 days after Tenant receives
written notice of such failure (or such longer period as shall be necessary to
cure any such failure that does not involve the payment of money, provided that
Tenant commences such cure within 30 days after receiving such notice and
pursues such cure to completion with diligence and continuity), Landlord shall
have the right to terminate this Lease by written notice to Tenant; provided,
however, if Tenant shall commence such cure within 30 days after receiving such
notice of termination and shall pursue such cure to completion with diligence
and continuity within 60 days after receiving such notice, Landlord's exercise
of such right to terminate this Lease pursuant to such notice shall be void.
Irrespective of whether Landlord exercises such right to terminate this Lease,
Landlord may proceed to protect and enforce its rights and remedies under this
Lease, at law or in equity, including without limitation an action seeking
specific performance of any agreement in this Lease or an injunction against a
violation of any of the terms of this Lease.  No failure or delay by Landlord in
exercising any right, power or remedy under this Lease, at law or in equity
shall operate as a waiver of such right, power or remedy; nor shall any single
or partial exercise of any such right, power or remedy preclude any other or
further exercise of such right, power or remedy or the exercise of any other
right, power or remedy under this Lease, at law or in equity.  The remedies
provided under this Section 13 or elsewhere in this Lease are cumulative and not
exclusive of any remedies provided by law.

     14.  Quiet Enjoyment.  If Tenant pays and performs fully and punctually all
          ---------------
of its obligations under this Lease, Tenant shall hold its rights, title and
interests in and to the Leased Premises for the Term free of claims that any
party holds any interest superior to this Lease in, the Leased Premises by,
through or under Landlord.  Tenant accepts the terms of the immediately
preceding sentence in lieu of any express or implied covenant of quiet
enjoyment, and Tenant waives and disclaims the benefit of any such covenant of
quiet enjoyment.  Landlord and Tenant acknowledge that this Lease is subject and
subordinate to the Reciprocal Easement Agreement dated November 28, 1998,
between Vesper Park, LLC, a Massachusetts limited liability company, and Dutton
Associates, Limited Partnership, a Delaware limited partnership, recorded with
Middlesex North Registry of Deeds at Book 10288, Page 144.  Landlord hereby
waives its right, under said Reciprocal Easement Agreement, to use the Pump
House and Pumping Equipment for the benefit of Lots 5 through 17 shown on the
Plan.

     14.  Notices.  Any notice, request or demand under this Lease shall be
          -------
shall be in writing and shall be effective when delivered by hand, upon refusal
of any delivery, two business days after being sent by registered or certified
mail, postage prepaid, return receipt requested, or

                                       19
<PAGE>

the day after when sent by a recognized overnight express service, with postage
prepaid. Any notice, request or demand by Tenant to Landlord shall be addressed
or delivered to Tenant at ____________________, with a copy to Testa, Hurwitz
and Thibeault, LLP, High Street Tower, 125 High Street, Boston, Massachusetts
02110, Attention: Real Estate Department, until otherwise directed in writing by
Landlord. Any notice or demand by Landlord to Tenant shall be addressed or
delivered to Landlord at 100 Vesper Executive Park, Tyngsboro, Massachusetts
01879, unless otherwise directed in writing by Landlord.

     15.  Binding Agreement.  This Lease shall bind and inure to the benefit of
          -----------------
Landlord, its successors and assigns, and Tenant and its successors or assigns
in connection with assignments and subleases permitted under the terms of this
Lease.

     16.  Entire Agreement. This Lease contains the entire agreement of Landlord
          ----------------
and Tenant concerning the Leased Premises and the other subjects addressed in
this Lease.

     17.  Written Modifications. This Lease may be amended, and the observance
          ---------------------
or performance of any obligation under this Lease may be waived (either
retroactively or proactively), with (and only with) the written consent of
Landlord and Tenant.  Any waiver shall be effective only in the specific
instance and for the specific purpose for which such waiver is given.

     18.  Partial Invalidity. If any provision of this Lease (or the application
          ------------------
of any provision of this Lease to any person or circumstances) shall be held
invalid or unenforceable to any extent, the remainder of this Lease (or the
application of such provision to other persons or circumstances) shall not be
affected, and each provision of this Lease shall be valid and enforceable to the
fullest extent permitted by law.

     19.  Governing Law. This Lease shall be governed, construed and interpreted
          -------------
in accordance with the laws of The Commonwealth of Massachusetts.

     20.  Counterparts.  This Lease may be executed in any number of
          ------------
counterparts, all of which taken together shall constitute one and the same
instrument, and Landlord and Tenant may each may execute this Lease by signing
any such counterpart.

     21.  Costs of Enforcement. In case of any litigation by Landlord and Tenant
          --------------------
concerning their respective rights or obligations under this Lease, the
unsuccessful party shall pay all reasonable costs and expenses, including
reasonable attorney's fees, incurred by the successful party in connection with
the enforcement of any such obligations.

     22.  Limitations on Liability.  Tenant shall neither assert nor seek to
          ------------------------
enforce any claim for breach of this Lease by Landlord against Landlord's assets
other than Landlord's interest in Lot 5, and Tenant shall look solely to such
interest for the satisfaction of any liability of Landlord under this Lease.
Neither Landlord, nor any successor holding Landlord's interests under this
Lease, nor any trustee or beneficiary of any trust holding Landlord's interests
under this Lease, nor any member, manager, partner, director, stockholder or
employee of Landlord shall ever be

                                       20
<PAGE>

personally liable to respond in monetary damages from assets other than
Landlord's interest in Lot 5. The foregoing provisions of this Section 22 shall
not limit any right that Tenant might otherwise have to obtain injunctive relief
against Landlord or Landlord's successors holding Landlord's interests under
this Lease. In no event shall Tenant ever be liable for any indirect or
consequential damages or loss of profits.

Landlord and Tenant execute this Lease as a sealed instrument.

TENANT:                                 LANDLORD:

[NAME]                                  [NAME]

By:_________________________________    By:__________________________________
Name:                                   Name:
Title:  President/Vice President        Title:  President/Vice President

By:_________________________________    By:__________________________________
Name:                                   Name:
Title:  Treasurer/Assistant Treasurer   Title:  Treasurer/Assistant Treasurer

                                       21

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