<PAGE>   1
                                                                   Exhibit 10.49

                         STANDARD FORM COMMERCIAL LEASE

                                                            215 FIRST STREET
                                                            CAMBRIDGE, MA 02142

1. PARTIES                 OLD CAMBRIDGE REALTY TRUST
   (fill in)               LESSOR, which expression shall include its heirs,
                           successors, and assigns where the context so admits,
                           does hereby lease to CHEMGENICS PHARMACEUTICALS, INC.
                           LESSEE, which expression shall include its
                           successors, executors, administrators, and assigns
                           where the context so admits, and the LESSEE hereby
                           leases the following described premises:




2. PREMISES                approximately one thousand and thirty-four (1,034)
   (fill in and include,   rentable square feet of office space on the second
   if applicable, suite    floor of Building 300 in the complex known as One
   number, floor           Kendall Square in Cambridge, Massachusetts and
   number, and square      further described on the attached Exhibit A: "the
   feet)                   Leased Premises" together with the right to use in
                           common with others entitled thereto, the hallways,
                           stairways, and elevators, necessary for access to
                           said leased premises, and lavatories nearest thereto.

3. TERM                    The term of this lease shall be for SIX (6) Months
   (fill in)               commencing on July 1, 1996 and ending on December 31,
                           1996.

4. RENT                    The LESSEE shall pay to the LESSOR fixed rent at the
   (fill in)               rate of $20,680.00 dollars per year, payable in
                           advance in monthly installments of 1723.33 subject to
                           proration in the case of any partial calendar month.
                           All rent shall be payable without offset or
                           deduction.

<PAGE>   2
7.  UTILITIES                 The LESSEE shall pay, as they become due, all
                              bills for electricity and other utilities (whether
                              they are used for furnishing heat or other
 *delete "air conditioning"   purposes) that are furnished to the leased
  if not applicable           premises and presently separately metered and all
                              bills for fuel furnished to a separate tank
                              servicing the leased premises exclusively.  The
                              LESSOR agrees to provide all other utility service
                              and to furnish reasonably hot and cold water and
                              reasonable heat and air conditioning* (except to
                              the extent that the same are furnished through
                              separately metered utilities or separate fuel
                              tanks as set forth above) to the leased premises,
                              the hallways, stairways, elevators, and lavatories
                              during normal business hours on regular business
                              days of the heating and air conditioning* seasons
                              of each year, to furnish elevator service and to
                              light passageways and stairways during business
                              hours, and to furnish each cleaning service as is
                              customary in similar buildings in said city or
                              town, all subject to interruption due to any
                              accident, to the making of repairs, alterations,
                              or improvements, to labor difficulties, to trouble
                              in obtaining fuel, electricity, service, or
                              supplies from the sources from which they are
                              usually obtained for said building, or to any
                              cause beyond the LESSOR's control.
                              *or billed on a pro-rata basis by Lessor.

                              LESSOR shall have no obligation to provide
                              utilities or equipment other than the utilities
                              and equipment within the premises as of the
                              commencement date of this lease.  In the event
                              LESSEE requires additional utilities or equipment,
                              the installation and maintenance thereof shall be
                              the LESSEE's sole obligation, provided that such
                              installation shall be subject to the written
                              consent of the LESSOR.

 8.  USE OF LEASED            The LESSEE shall use the leased premises only for
     PREMISES                 the purpose of office use in connection with its
     (fill in)                biotechnology and research operations.

 9.  COMPLIANCE               The LESSEE acknowledges that no trade or
     WITH LAWS                occupation shall be conducted in the leased
                              premises or use made thereof which will be
                              unlawful, improper, noisy or offensive, or
                              contrary to any law or any municipal by-law or
                              ordinance in force in the city or town in which
                              the premises are situated.  Without limiting the
                              generality of the foregoing (a) the LESSEE shall
                              not bring or permit to be brought or kept in or on
                              the leased premises or elsewhere on the LESSOR's
                              property any hazardous, toxic, inflammable,
                              combustible or explosive fluid, material, chemical
                              or substance, including without limitation any
                              item defined as hazardous pursuant to Chapter 21E
                              of the Massachusetts General Laws; and (b) the
                              LESSEE shall be responsible for compliance with
                              requirements imposed by the Americans with
                              Disabilities Act relative to the layout of the
                              leased premises and any work performed by the
                              LESSEE therein.

10.  FIRE INSURANCE           The LESSEE shall not permit any use of the leased
                              premises which will make voidable any insurance on
                              the property of which the leased premises are a
                              part, or on the contents of said property or which
                              shall be contrary to any law or regulation from
                              time to time established by the New England Fire
                              Insurance Rating Association, or any similar body
                              succeeding to its powers.  The LESSEE shall on
                              demand reimburse the LESSOR, and all other
                              tenants, all extra insurance premiums caused by
                              the LESSEE's use of the premises.

11.  MAINTENANCE              The LESSEE agrees to maintain the leased premises
                              in good condition, damage by fire and other
     A.  LESSEE'S             casualty only excepted, and whenever necessary,
         OBLIGATIONS          to replace plate glass and other glass therein,
                              acknowledging that the leased premises are now in
                              good order and the glass whole.  The LESSEE shall
                              not permit the leased premises to be overloaded,
                              damaged, stripped, or defaced, nor suffer any
                              waste.  LESSEE shall obtain written consent of
                              LESSOR before erecting any sign on the premises.

     B.  LESSOR'S             The LESSOR agrees to maintain the structure of the
         OBLIGATIONS          building of which the leased premises are a part
                              in the same condition as it is at the commencement
                              of the term or as it may be put in during the term
                              of this lease, reasonable wear and tear, damage by
                              fire and other casualty only excepted, unless such
                              maintenance is required because of the LESSEE or
                              those for whose conduct the LESSEE is legally
                              responsible.

12.  ALTERATIONS --           The LESSEE shall not make structural alterations
     ADDITIONS                or additions to the leased premises, but may make
                              non-structural alterations provided the LESSOR
                              consents thereto in writing, which consent shall
                              not be unreasonably withheld or delayed.  All such
                              allowed alterations shall be at LESSEE's expense
                              and shall be in quality at least equal to the
                              present construction.  LESSEE shall not permit any
                              mechanics' liens, or similar liens, to remain upon
                              the leased premises for labor and material
                              furnished to LESSEE or claimed to have been
                              furnished to LESSEE in connection with  work of
                              any character performed or claimed to have been
                              performed at the direction of LESSEE and shall
                              cause any such lien to be released of record
                              forthwith without cost to LESSOR.  Any alterations
                              or improvements made by the LESSEE shall become
                              the property of the LESSOR at the termination of
                              the occupancy as provided herein.

13.  ASSIGNMENT --            The LESSEE shall not assign or sublet the whole or
     SUBLEASING               any part of the leased premises without LESSOR's
                              prior written consent.  Notwithstanding such
                              consent, LESSEE shall remain liable to LESSOR for
                              the payment of all rent and for the full
                              performance of the covenants and conditions of
                              this lease.


<PAGE>   3
14. SUBORDINATION       This lease shall be subject and subordinate to any and
                        all mortgages, deeds of trust and other instruments in
                        the nature of a mortgage, now or at any time hereafter,
                        a lien or liens on the property of which the leased
                        premises are a part and the LESSEE shall, when
                        requested, promptly execute and deliver such written
                        instruments as shall be necessary to show the
                        subordination of this lease to said mortgages, deeds of
                        trust or other such instruments in the nature of a
                        mortgage.

15. LESSOR'S            The LESSOR or agents of the LESSOR may, at reasonable
    ACCESS              times, enter to view the leased premises and may remove
                        placards and signs not approved and affixed as herein
                        provided, and make repairs and alterations as LESSOR
                        should elect to do and may show the leased premises to
                        others, and at any time within three (3) months before
                        the expiration of the term, may affix to any suitable
                        part of the leased premises a notice for letting or
                        selling the leased premises or property of which the
                        leased premises are a part and keep the same so affixed
                        without hindrance or molestation.

16. INDEMNIFICATION     The LESSEE shall save the LESSOR harmless from all loss
    AND LIABILITY       and damage occasioned by anything occurring on the
    (fill in)           leased premises unless caused by the negligence or
                        misconduct of the LESSOR, and from all loss and damage
                        wherever occurring occasioned by any omission, fault,
                        neglect or other misconduct of the LESSEE. The removal
                        of snow and ice from the sidewalks bordering upon the
                        leased premises shall be LESSOR's responsibility.

17. LESSEE'S            The LESSEE shall maintain with respect to the leased
    LIABILITY           premises and the property of which the leased premises
    INSURANCE           are a part comprehensive public liability insurance in
    (fill in)           the amount of $1,000,000 with property damage insurance
                        in limits of $500,000 in responsible companies qualified
                        to do business in Massachusetts and in good standing
                        therein insuring the LESSOR as well as LESSEE against
                        injury to persons or damage to property as provided. The
                        LESSEE shall deposit with the LESSOR certificates for
                        such insurance at or prior to the commencement of the
                        term, and thereafter within thirty (30) days prior to
                        the expiration of any such policies. All such insurance
                        certificates shall provide that such policies shall not
                        be cancelled without at least ten (10) days prior
                        written notice to each assured named therein.

18. FIRE,               Should a substantial portion of the leased premises, or
    CASUALTY --         of the property of which they are a part, be
    EMINENT             substantially damaged by fire or other casualty, or be
    DOMAIN              taken by eminent domain, the LESSOR may elect to
                        terminate this lease. When such fire, casualty, or
                        taking renders the leased premises substantially
                        unsuitable for their intended use, a just and
                        proportionate abatement of rent shall be made, and the
                        LESSEE may elect to terminate this lease if:

                                (a) The LESSOR fails to give written notice
                                    within thirty (30) days of intention to
                                    restore leased premises, or

                                (b) The LESSOR fails to restore the leased
                                    premises to a condition substantially
                                    suitable for their intended use within
                                    ninety (90) days of said fire, casualty or
                                    taking.

                        The LESSOR reserves, and the LESSEE grants to the
                        LESSOR, all rights which the LESSEE may have for damages
                        or injury to the leased premises for any taking by
                        eminent domain, except for damage to the LESSEE's
                        fixtures, property, or equipment.

19. DEFAULT             In the event that:
    AND
    BANKRUPTCY                  (a) The LESSEE shall default in the payment of
    (fill in)                       any installment of rent or other sum herein
                                    specified and such default shall continue
                                    for ten (10) days after written notice
                                    thereof; or

                                (b) The LESSEE shall default in the observance
                                    or performance of any other of the LESSEE's
                                    covenants, agreements, or obligations
                                    hereunder and such default shall not be
                                    corrected within thirty (30) days after
                                    written notice thereof; or

                                (c) The LESSEE shall be declared bankrupt or
                                    insolvent according to law, or, if any
                                    assignment shall be made of LESSEE's
                                    property for the benefit of creditors,

                        then the LESSOR shall have the right thereafter, while
                        such default continues, to re-enter and take complete
                        possession of the leased premises, to declare the term
                        of this lease ended, and remove the LESSEE's effects,
                        without prejudice to any remedies which might be
                        otherwise used for arrears of rent or other default. The
                        LESSEE shall indemnify the LESSOR against all loss of
                        rent and other payments which the LESSOR may incur by
                        reason of such termination during the residue of the
                        term.  If the LESSEE shall default, after reasonable
                        notice thereof, in the observance or performance of any
                        conditions or covenants on LESSEE's part to be observed
                        or performed under or by virtue of any of the provisions
                        in any article of this lease, the LESSOR, without being
                        under any obligation to do so and without thereby
                        waiving such default, may remedy such default for the
                        account and at the expense of the LESSEE. If the LESSOR
                        makes any expenditures or incurs any obligations for the
                        payment of money in connection therewith, including but
                        not limited to, reasonable attorney's fees in
                        instituting, prosecuting or defending any action or
                        proceeding, such sums paid or obligations insured, with
                        interest at the rate of 12 percent per annum and costs,
                        shall be paid to the LESSOR by the LESSEE as additional
                        rent.

20. NOTICE              Any notice from the LESSOR to the LESSEE relating to the
    (fill in)           leased premises or to the occupancy thereof, shall be
                        deemed duly served, if left at the leased premises
                        addressed to the LESSEE, or if mailed to the leased
                        premises, registered or certified mail, return receipt
                        requested, postage prepaid, addressed to the LESSEE. Any
                        notice from the LESSEE to the LESSOR relating to the
                        leased premises or to the occupancy thereof, shall be
                        deemed duly served, if mailed to the LESSOR by
                        registered or certified mail, return receipt requested,
                        postage prepaid, addressed to the LESSOR at such address
                        as the LESSOR may from time to time advise in writing.
                        All rent notices shall be paid and sent to the LESSOR at
                        Old Cambridge Realty Trust c/o The Athenaeum Group, 215
                        First St., Camb. MA 02142.

21. SURRENDER           The LESSEE shall at the expiration or other termination
                        of this lease remove all LESSEE's goods and effects from
                        the leased premises, (including, without hereby limiting
                        the generality of the foregoing, all signs and lettering
                        affixed or painted by the LESSEE, either inside or
                        outside the leased premises). LESSEE shall deliver to
                        the LESSOR the leased premises and all keys, locks
                        thereto, and other fixtures connected therewith and all
                        alterations and additions made to or upon the leased
                        premises, in good conditions, damage by fire or other
                        casualty only excepted. In the event of the LESSEE's
                        failure to remove any of LESSEE's property from the
                        premises, LESSOR is hereby authorized, without liability
                        to LESSEE for loss or damage thereto, and at the sole
                        risk of LESSEE to remove and store any of the property
                        at LESSEE's expense, or to retain same
<PAGE>   4
                        to apply the net proceeds of such sale to the payment of
                        any sum due hereunder, or to destroy such property.

22. BROKERAGE
    (fill in or delete)



23. CONDITION OF        Except as may be otherwise expressly set forth herein,
    PREMISES            the LESSEE shall accept the leased premises "as is" in
                        their condition as of the commencement of the term of
                        this lease, and the LESSOR shall be obligated to perform
                        no work whatsoever in order to prepare the leased
                        premises for occupancy by the LESSEE.

24. FORCE               In the event that the LESSOR is prevented or delayed
    MAJEURE             from making any repairs or performing any other covenant
                        hereunder by reason of any cause reasonably beyond the
                        control of the LESSOR, the LESSOR shall not be liable to
                        the LESSEE therefor nor, except as expressly otherwise
                        provided in case of casualty or taking, shall the LESSEE
                        be entitled to any abatement or reduction of rent by
                        reason thereof, nor shall the same give rise to a claim
                        by the LESSEE that such failure constitutes actual or
                        constructive eviction from the leased premises or any
                        part thereof.

25. LATE                If rent or any other sum payable hereunder remains
    CHARGE              outstanding for a period of ten (10) days, the LESSEE
                        shall pay to the LESSOR a late charge equal to one and
                        one-half percent (1.5%) of the amount due for each month
                        or portion thereof during which the arrearage continues.

26. LIABILITY           No owner of the property of which the leased premises
    OF OWNER            are a part shall be liable hereunder except for breaches
                        of the LESSOR's obligations occurring during the period
                        of such ownership. The obligations of the LESSOR shall
                        be binding upon the LESSOR's interest in said property,
                        but not upon other assets of the LESSOR, and no
                        individual partner, agent, trustee, stockholder,
                        officer, director, employee or beneficiary of the LESSOR
                        shall be personally liable for performance of the
                        LESSOR's obligations hereunder.

27. OTHER               It is also understood and agreed that
    PROVISIONS
                        1.  Lessee will have two (2) six (6) month options to
                            renew this lease with two (2) month written notice
                            to Landlord. The Base Rent for the first six-month
                            option will be $21,714.00 per annum. The Base Rent
                            for the second six (6) month option will be
                            $22,748.00 per annum.



IN WITNESS WHEREOF, the said parties hereunto set their hands and seals this
__________________ day of JUNE 1996.

CHEMGENICS PHARMACEUTICALS, INC.        OLD CAMBRIDGE REALTY TRUST

        [SIG]
-----------------------------------     -------------------------------------
LESSEE  (DULY AUTHORIZED)                       ROBERT A. JONES, TRUSTEE
                                        LESSOR

/s/  KIM LARSON
-----------------------------------     -------------------------------------
WITNESS                                 WITNESS

                        --------------------------------
                        BROKER(S)
<PAGE>   5
                                   EXHIBIT A

                               "LEASED PREMISES"

<TABLE>
<CAPTION>
Suite #         Use             Area
<S>             <C>             <C>
 201             OF             5889
 202             OF             1810
 203             OF              654
 204             OF              432
 205             SIG             195
 206             SIG              84
 207             OF             1034
 208             OF              940
</TABLE>

                            [FLOORPLAN ILLUSTRATION]

                                                                Rev.
[LOGO]  ONE KENDALL SQUARE  BUILDING 300  SECOND FLOOR          March 16, 1994
<PAGE>   6


                         STANDARD FORM COMMERCIAL LEASE


1. PARTIES                 OLD CAMBRIDGE REALTY TRUST
   (fill in)               LESSOR, which expression shall include its heirs,
                           successors, and assigns where the context so admits,
                           does hereby lease to MYCO PHARMACEUTICALS, INC.
                           LESSEE, which expression shall include its
                           successors, executors, administrators, and assigns
                           where the context so admits, and the LESSEE hereby
                           leases the following described premises:




2. PREMISES                approximately nine hundred and fourteen (914)
   (fill in and include,   rentable square feet of office space on the ground
   if applicable, suite    (basement) floor of Building 300 in the office
   number, floor           complex known as One Kendall Square in Cambridge,
   number, and square      Massachusetts and further described on the attached
   feet)                   Exhibit A: "LEASED PREMISES" together with the right
                           to use in common, with others entitled thereto, the
                           hallways, stairways, and elevators, necessary for
                           access to said leased premises, and lavatories
                           nearest thereto.

3. TERM                    The term of this lease shall be for One (1) Year
   (fill in)               commencing on August 1, 1995* and ending on July 31,
                           1996.**

4. RENT                    The LESSEE shall pay to the LESSOR rent at the rate
   (fill in)               of $8,226.00 dollars per year, payable in advance
                           in monthly installments of $685.50.


                           *  or upon occupancy, whichever is earlier.  If early
                              occupancy occurs, rent will be due on a pro-rata,
                              daily basis.

                           ** and continuing thereafter until either party gives
                              the other three (3) months notice.
<PAGE>   7
7.  UTILITIES                 The LESSEE shall pay, as they become due, all
                              bills for electricity and other utilities (whether
                              they are used for furnishing heat or other
 *delete "air conditioning"   purposes) that are furnished to the leased
  if not applicable           premises and presently separately metered,* and
                              all bills for fuel furnished to a separate tank
                              servicing the leased premises exclusively.  The
                              LESSOR agrees to provide all other utility service
                              and to furnish reasonably hot and cold water and
                              reasonable heat and air conditioning* (except to
                              the extent that the same are furnished through
                              separately metered utilities or separate fuel
                              tanks as set forth above) to the leased premises,
                              the hallways, stairways, elevators, and lavatories
                              during normal business hours on regular business
                              days of the heating and air conditioning* seasons
                              of each year, to furnish elevator service and to
                              light passageways and stairways during business
                              hours, and to furnish such cleaning service as is
                              customary in similar buildings in said city or
                              town, all subject to interruption due to any
                              accident, to the making of repairs, alterations,
                              or improvements, to labor difficulties, to trouble
                              in obtaining fuel, electricity, service, or
                              supplies from the sources from which they are
                              usually obtained for said building, or to any
                              cause beyond the LESSOR's control.
                                *or, if not separately metered, as billed by
                                 Lessor on a pro-rata basis.

                              LESSOR shall have no obligation to provide
                              utilities or equipment other than the utilities
                              and equipment within the premises as of the
                              commencement date of this lease.  In the event
                              LESSEE requires additional utilities or equipment,
                              the installation and maintenance thereof shall be
                              the LESSEE's sole obligation, provided that such
                              installation shall be subject to the written
                              consent of the LESSOR.

 8.  USE OF LEASED            The LESSEE shall use the leased premises only for
     PREMISES                 the purpose of general offices and storage.
     (fill in)

 9.  COMPLIANCE               The LESSEE acknowledges that no trade or
     WITH LAWS                occupation shall be conducted in the leased
                              premises or use made thereof which will be
                              unlawful, improper, noisy or offensive, or
                              contrary to any law or any municipal by-law or
                              ordinance in force in the city or town in which
                              the premises are situated.

10.  FIRE INSURANCE           The LESSEE shall not permit any use of the leased
                              premises which will make voidable any insurance on
                              the property of which the leased premises are a
                              part, or on the contents of said property or which
                              shall be contrary to any law or regulation from
                              time to time established by the New England Fire
                              Insurance Rating Association, or any similar body
                              succeeding to its powers.  The LESSEE shall on
                              demand reimburse the LESSOR, and all other
                              tenants, all extra insurance premiums caused by
                              the LESSEE's use of the premises.

11.  MAINTENANCE              The LESSEE agrees to maintain the leased premises
                              in good condition, damage by fire and other
     A.  LESSEE'S             casualty only excepted, and whenever necessary,
         OBLIGATIONS          to replace plate glass and other glass therein,
                              acknowledging that the leased premises are now in
                              good order and the glass whole.  The LESSEE shall
                              not permit the leased premises to be overloaded,
                              damaged, stripped, or defaced, nor suffer any
                              waste.  LESSEE shall obtain written consent of
                              LESSOR before erecting any sign on the premises.

     B.  LESSOR'S             The LESSOR agrees to maintain the structure of the
         OBLIGATIONS          building of which the leased premises are a part
                              in the same condition as it is at the commencement
                              of the term or as it may be put in during the term
                              of this lease, reasonable wear and tear, damage by
                              fire and other casualty only excepted, unless such
                              maintenance is required because of the LESSEE or
                              those for whose conduct the LESSEE is legally
                              responsible.

12.  ALTERATIONS --           The LESSEE shall not make structural alterations
     ADDITIONS                or additions to the leased premises, but may make
                              non-structural alterations provided the LESSOR
                              consents thereto in writing, which consent shall
                              not be unreasonably withheld or delayed.  All such
                              allowed alterations shall be at LESSEE's expense
                              and shall be in quality at least equal to the
                              present construction.  LESSEE shall not permit any
                              mechanics' liens, or similar liens, to remain upon
                              the leased premises for labor and material
                              furnished to LESSEE or claimed to have been
                              furnished to LESSEE in connection with work of
                              any character performed or claimed to have been
                              performed at the direction of LESSEE and shall
                              cause any such lien to be released of record
                              forthwith without cost to LESSOR.  Any alterations
                              or improvements made by the LESSEE shall become
                              the property of the LESSOR at the termination of
                              the occupancy as provided herein.

13.  ASSIGNMENT --            The LESSEE shall not assign or sublet the whole or
     SUBLEASING               any part of the leased premises without LESSOR's
                              prior written consent.  Notwithstanding such
                              consent, LESSEE shall remain liable to LESSOR for
                              the payment of all rent and for the full
                              performance of the covenants and conditions of
                              this lease.


<PAGE>   8
14. SUBORDINATION       This lease shall be subject and subordinate to any and
                        all mortgages, deeds of trust and other instruments in
                        the nature of a mortgage, now or at any time hereafter,
                        a lien or liens on the property of which the leased
                        premises are a part and the LESSEE shall, when
                        requested, promptly execute and deliver such written
                        instruments as shall be necessary to show the
                        subordination of this lease to said mortgages, deeds of
                        trust or other such instruments in the nature of a
                        mortgage.

15. LESSOR'S            The LESSOR or agents of the LESSOR may, at reasonable
    ACCESS              times, enter to view the leased premises and may remove
                        placards and signs not approved and affixed as herein
                        provided, and make repairs and alterations as LESSOR
                        should elect to do and may show the leased premises to
                        others, and at any time within three (3) months before
                        the expiration of the term, may affix to any suitable
                        part of the leased premises a notice for letting or
                        selling the leased premises or property of which the
                        leased premises are a part and keep the same so affixed
                        without hindrance or molestation.

16. INDEMNIFICATION     The LESSEE shall save the LESSOR harmless from all loss
    AND LIABILITY       and damage occasioned by the use or escape of water or
                        by the bursting of pipes, as well as from any claim or
                        damage resulting from neglect in not removing snow and
                        ice from the roof of the building or from the sidewalks
                        bordering upon the premises so leased, or by any
                        nuisance made or suffered on the leased premises, unless
                        such loss is caused by the neglect of the LESSOR.  The
                        removal of snow and ice from the sidewalks bordering
                        upon the leased premises shall be LESSOR's
                        responsibility.

17. LESSEE'S            The LESSEE shall maintain with respect to the leased
    LIABILITY           premises and the property of which the leased premises
    INSURANCE           are a part comprehensive public liability insurance in
    (fill in)           the amount of $1,000,000 with property damage insurance
                        in limits of $100,000 in responsible companies qualified
                        to do business in Massachusetts and in good standing
                        therein insuring the LESSOR as well as LESSEE against
                        injury to persons or damage to property as provided. The
                        LESSEE shall deposit with the LESSOR certificates for
                        such insurance at or prior to the commencement of the
                        term, and thereafter within thirty (30) days prior to
                        the expiration of any such policies. All such insurance
                        certificates shall provide that such policies shall not
                        be cancelled without at least ten (10) days prior
                        written notice to each assured named therein.

18. FIRE,               Should a substantial portion of the leased premises, or
    CASUALTY --         of the property of which they are a part, be
    EMINENT             substantially damaged by fire or other casualty, or be
    DOMAIN              taken by eminent domain, the LESSOR may elect to
                        terminate this lease. When such fire, casualty, or
                        taking renders the leased premises substantially
                        unsuitable for their intended use, a just and
                        proportionate abatement of rent shall be made, and the
                        LESSEE may elect to terminate this lease if:

                                (a) The LESSOR fails to give written notice
                                    within thirty (30) days of intention to
                                    restore leased premises, or

                                (b) The LESSOR fails to restore the leased
                                    premises to a condition substantially
                                    suitable for their intended use within
                                    ninety (90) days of said fire, casualty or
                                    taking.

                        The LESSOR reserves, and the LESSEE grants to the
                        LESSOR, all rights which the LESSEE may have for damages
                        or injury to the leased premises for any taking by
                        eminent domain, except for damage to the LESSEE's
                        fixtures, property, or equipment.

19. DEFAULT             In the event that:
    AND
    BANKRUPTCY                  (a) The LESSEE shall default in the payment of
    (fill in)                       any installment of rent or other sum herein
                                    specified and such default shall continue
                                    for ten (10) days after written notice
                                    thereof; or

                                (b) The LESSEE shall default in the observance
                                    or performance of any other of the LESSEE's
                                    covenants, agreements, or obligations
                                    hereunder and such default shall not be
                                    corrected within thirty (30) days after
                                    written notice thereof; or

                                (c) The LESSEE shall be declared bankrupt or
                                    insolvent according to law, or, if any
                                    assignment shall be made of LESSEE's
                                    property for the benefit of creditors,

                        then the LESSOR shall have the right thereafter, while
                        such default continues, to re-enter and take complete
                        possession of the leased premises, to declare the term
                        of this lease ended, and remove the LESSEE's effects,
                        without prejudice to any remedies which might be
                        otherwise used for arrears of rent or other default. The
                        LESSEE shall indemnify the LESSOR against all loss of
                        rent and other payments which the LESSOR may incur by
                        reason of such termination during the residue of the
                        term.  If the LESSEE shall default, after reasonable
                        notice thereof, in the observance or performance of any
                        conditions or covenants on LESSEE's part to be observed
                        or performed under or by virtue of any of the provisions
                        in any article of this lease, the LESSOR, without being
                        under any obligation to do so and without thereby
                        waiving such default, may remedy such default for the
                        account and at the expense of the LESSEE. If the LESSOR
                        makes any expenditures or incurs any obligations for the
                        payment of money in connection therewith, including but
                        not limited to, reasonable attorney's fees in
                        instituting, prosecuting or defending any action or
                        proceeding, such sums paid or obligations insured, with
                        interest at the rate of 12 percent per annum and costs,
                        shall be paid to the LESSOR by the LESSEE as additional
                        rent.

20. NOTICE              Any notice from the LESSOR to the LESSEE relating to the
    (fill in)           leased premises or to the occupancy thereof, shall be
                        deemed duly served, if left at the leased premises
                        addressed to the LESSEE, or if mailed to the leased
                        premises, registered or certified mail, return receipt
                        requested, postage prepaid, addressed to the LESSEE. Any
                        notice from the LESSEE to the LESSOR relating to the
                        leased premises or to the occupancy thereof, shall be
                        deemed duly served, if mailed to the LESSOR by
                        registered or certified mail, return receipt requested,
                        postage prepaid, addressed to the LESSOR at such address
                        as the LESSOR may from time to time advise in writing.
                        All rent notices shall be paid and sent to the LESSOR at
                        Old Cambridge Realty Trust c/o The Athenaeum Group, 215
                        First St., Camb. MA 02142.
<PAGE>   9
21. SURRENDER           The LESSEE shall at the expiration or other termination
                        of this lease remove all LESSEE's goods and effects from
                        the leased premises, (including, without hereby limiting
                        the generality of the foregoing, all signs and lettering
                        affixed or painted by the LESSEE, either inside or
                        outside the leased premises), LESSEE shall deliver to
                        the LESSOR the leased premises and all keys, locks
                        thereto, and other fixtures connected therewith and all
                        alterations and additions made to or upon the leased
                        premises, in good condition, damage by fire or other
                        casualty only excepted.  In the event of the LESSEE's
                        failure to remove any of LESSEE's property from the
                        premises, LESSOR is hereby authorized, without liability
                        to LESSEE for loss or damage thereto, and at the sole
                        risk of LESSEE, to remove and store any of the property
                        at LESSEE's expense, or to retain same under LESSOR's
                        control or to sell at public or private sale, without
                        notice any or all of the property not so removed and to
                        apply the net proceeds of such sale to the payment of
                        any sum due hereunder, or to destroy such property.

22. BROKERAGE           [Deleted]
    (fill in or delete)

23. OTHER               It is also understood and agreed that
    PROVISIONS
                        1.  THE LEASED PREMISES WILL BE ACCEPTED AND DELIVERED
                            IN THEIR CURRENT "AS IS" CONFIGURATION AND
                            CONDITION, WITH THE LESSOR RESPONSIBLE FOR A GENERAL
                            CLEANING AND CHANGING OF THE LOCK AND KEY.

                        2.  LESSEE SHALL BE RESPONSIBLE FOR ITS PRO-RATA SHARE
                            OF REAL ESTATE TAXES AND COMMON AREA MAINTENANCE
                            (CAM) CHARGES, AS BILLED BY THE LESSOR ON A PRO-RATA
                            BASIS.  UPON WRITTEN REQUEST, LESSEE MAY REVIEW
                            LESSOR'S ACCOUNTING AND BILLING FOR REASONABLENESS.

                        3.  LESSEE SHALL HAVE THE RIGHT TO LEASE TWO (2)
                            ADDITIONAL PARKING SPACES IN THE OKS GARAGE AT THE
                            RATE OF $115. PER VEHICLE MONTHLY FOR THE TERM OF
                            THE LEASE.


IN WITNESS WHEREOF, the said parties hereunto set their hands and seals this
__________________ day of __________________ , 1995.

MYCO PHARMACEUTICALS, INC.              OLD CAMBRIDGE REALTY TRUST

/s/  BARRY BERKOWITZ
-----------------------------------     -------------------------------------
LESSEE  (DULY AUTHORIZED)                       ROBERT A. JONES, TRUSTEE
                                        LESSOR

        [SIG]
-----------------------------------     -------------------------------------
WITNESS                                 WITNESS

<PAGE>   10
                                   EXHIBIT A

                               "LEASED PREMISES"

<TABLE>
<CAPTION>
Suite #         Use             Area          Suite #           Use        Area
  <S>           <C>             <C>             <C>             <C>        <C>
  001           RE               914            010             SIG         638
  002           LAB             2349            011             SIG         515
  003           RE              3154
  005           SIG              365
  006           SIG              208
  007           SIG              120
  008           SIG              215
  009           SIG              215
</TABLE>

                            [FLOORPLAN ILLUSTRATION]

                                                                Rev.
[LOGO]  ONE KENDALL SQUARE  BUILDING 300  LOWER LEVEL           July 29, 1993