Document:

<PAGE>

                                                                Exhibit 10.21(c)

                                                        TIAA Appl. #AAA1280
                                                        TIAA Mtge. # M - 0005296

                                 PROMISSORY NOTE

$9,900,000.00                                           Denver, Colorado
                                                        Dated: December 23, 2002

          FOR VALUE RECEIVED, AMERIVEST KELLOGG INC., a Colorado corporation
("Borrower") having its principal place of business at 1780 S. Bellaire Street,
Suite 515, Denver, Colorado 80222, promises to pay to TEACHERS INSURANCE AND
ANNUITY ASSOCIATION OF AMERICA ("Lender"), a New York corporation, or order, at
Lender's offices at 730 Third Avenue, New York, New York 10017 or at such other
place as Lender designates in writing, the principal sum of NINE MILLION, NINE
HUNDRED THOUSAND AND NO/100s DOLLARS ($9,900,000.00) (the principal sum or so
much of the principal sum as may be advanced and outstanding from time to time,
the "Principal"), in lawful money of the United States of America, with interest
on the Principal from the date of this Promissory Note (this "Note") through and
including January 1, 2013 (the "Maturity Date") at the fixed rate of seven and
four tenths percent (7.40%) per annum (the "Fixed Interest Rate").

          This Note is secured by, among other things, the Deed of Trust,
Assignment of Leases and Rents, Security Agreement, and Fixture Filing Statement
(the "Deed of Trust") dated the date of this Note made by Borrower for the
benefit of Lender as security for the Loan. All capitalized terms not expressly
defined in this Note will have the definitions set forth in the Deed of Trust.

     Section 1. Payments of Principal and Fixed Interest.

          a. Borrower will make monthly installment payments ("Debt Service
Payments") as follows:

               (i) On January 1, 2003, a payment of accrued interest on the
     Principal at the Fixed Interest Rate; and

               (ii) On February 1, 2003 and on the first day of each succeeding
     calendar month through and including January 1, 2013, payments in the
     amount of Seventy-Two Thousand Five Hundred Seventeen Dollars and Fifty
     Cents ($72,517.50), each of which will be applied first to interest on the
     Principal at the Fixed Interest Rate and then to the Principal.

          b. On the Maturity Date, Borrower will pay the Principal in full
together with accrued interest at the Fixed Interest Rate and all other amounts
due under the Loan Documents.

     Section 2. Prepayment Provisions.

          a. The following definitions apply:

          "Discount Rate" means the yield on a U.S. Treasury issue selected by
Lender, as published in the Wall Street Journal, two weeks prior to prepayment,
having a maturity date

                                       1

<PAGE>

corresponding (or most closely corresponding, if not identical) to the Maturity
Date, and, if applicable, a coupon rate corresponding (or most closely
corresponding, if not identical) to the Fixed Interest Rate.

          "Default Discount Rate" means the Discount Rate less 300 basis points.

          "Discounted Value" means the Discounted Value of a Note Payment based
on the following formula:

             NP
          (1 + R/12)n  =  Discounted Value

          NP       =      Amount of Note Payment

          R        =      Discount Rate or Default Discount Rate as the case may
                          be.

          n        =      The number of months between the date of prepayment
                          and the scheduled date of the Note Payment being
                          discounted rounded to the nearest integer.

          "Note Payments" means (i) the scheduled Debt Service Payments for the
period from the date of prepayment through the Maturity Date and (ii) the
scheduled repayment of Principal, if any, on the Maturity Date.

          "Prepayment Date Principal" means the Principal on the date of
prepayment.

          b. This Note may not be prepaid in full or in part before January 1,
2008. Commencing on January 1, 2008, provided there is no Event of Default,
Borrower may prepay this Note in full, but not in part, on the first day of any
calendar month, upon 60 days prior notice to Lender and upon payment in full of
the Debt which will include a payment (the "Prepayment Premium") equal to the
greater of (i) an amount equal to the product of 1% times the Prepayment Date
Principal and (ii) the amount by which the sum of the Discounted Values of Note
Payments, calculated at the Discount Rate, exceeds the Prepayment Date
Principal. Provided there is no Event of Default, this Note may be prepaid in
full without payment of the Prepayment Premium during the last 90 days of the
Term. This Note may not be prepaid without simultaneous prepayment in full of
any other notes secured by the Loan Documents. Notwithstanding the foregoing,
this Note may be prepaid in part in accordance with Section 4 of the
Cross-Collateralization and Cross-Default Agreement of even date herewith under
the circumstances set forth therein.

          c. After an Event of Default or upon any prepayment not permitted by
the Loan Documents, any tender of payment of the amount necessary to satisfy all
or any part of the Debt, any decree of foreclosure, any statement of the amount
due at the time of foreclosure (including foreclosure by power of sale) and any
tender of payment during any redemption period after foreclosure, will include
an amount (the "Evasion Premium") equal to the greater of (i) an amount equal to
the product of 1% plus 300 basis points times the Prepayment Date Principal, and
(ii) the amount by which the sum of the Discounted Values of the Note Payments,
calculated at the Default Discount Rate, exceeds the Prepayment Date Principal.

                                       2

<PAGE>

          d. Borrower acknowledges that:

               (i) a prepayment will cause damage to Lender;

               (ii) the Evasion Premium is intended to compensate Lender for the
     loss of its investment and the expense incurred and time and effort
     associated with making the Loan, which will not be fully repaid if the Loan
     is prepaid;

               (iii) it will be extremely difficult and impractical to ascertain
     the extent of Lender's damages caused by a prepayment after an Event of
     Default or any other prepayment not permitted by the Loan Documents; and

               (iv) the Evasion Premium represents Lender and Borrower's
     reasonable estimate of Lender's damages for the prepayment and is not a
     penalty.

     Section 3. Events of Default:

          a. It is an "Event of Default" under this Note:

               (i) if Borrower fails to pay any amount due, as and when
     required, under this Note or any other Loan Document and the failure
     continues for a period of 5 days; or

               (ii) if an Event of Default occurs under any other Loan Document.

          b. If an Event of Default occurs, Lender may declare all or any
portion of the Debt immediately due and payable ("Acceleration") and exercise
any of the other Remedies.

     Section 4. Default Rate. Interest on the Principal will accrue at the
Default Interest Rate from the date an Event of Default occurs.

     Section 5. Late Charges.

          a. If Borrower fails to pay any Debt Service Payment when due and the
failure continues for a period of 5 days or more or fails to pay any amount due
under the Loan Documents on the Maturity Date, Borrower agrees to pay to Lender
an amount (a "Late Charge") equal to five cents ($.05) for each one dollar
($1.00) of the delinquent payment.

          b. Borrower acknowledges that:

               (i) a delinquent payment will cause damage to Lender;

               (ii) the Late Charge is intended to compensate Lender for loss of
     use of the delinquent payment and the expense incurred and time and effort
     associated with recovering the delinquent payment;

               (iii) it will be extremely difficult and impractical to ascertain
     the extent of Lender's damages caused by the delinquency; and

                                       3

<PAGE>

               (iv) the Late Charge represents Lender and Borrower's reasonable
     estimate of Lender's damages from the delinquency and is not a penalty.

     Section 6. Limitation of Liability. This Note is subject to the limitations
on liability set forth in the Article of the Deed of Trust entitled "Limitation
of Liability."

     Section 7. WAIVERS. IN ADDITION TO THE WAIVERS SET FORTH IN THE ARTICLE OF
THE DEED OF TRUST ENTITLED "WAIVERS," BORROWER WAIVES PRESENTMENT FOR PAYMENT,
DEMAND, DISHONOR AND, EXCEPT AS EXPRESSLY SET FORTH IN THE LOAN DOCUMENTS,
NOTICE OF ANY OF THE FOREGOING. BORROWER FURTHER WAIVES ANY PROTEST, LACK OF
DILIGENCE OR DELAY IN COLLECTION OF THE DEBT OR ENFORCEMENT OF THE LOAN
DOCUMENTS. BORROWER AND ALL INDORSERS, SURETIES AND GUARANTORS OF THE
OBLIGATIONS CONSENT TO ANY EXTENSIONS OF TIME, RENEWALS, WAIVERS AND
MODIFICATIONS THAT LENDER MAY GRANT WITH RESPECT TO THE OBLIGATIONS AND TO THE
RELEASE OF ANY SECURITY FOR THIS NOTE AND AGREE THAT ADDITIONAL MAKERS MAY
BECOME PARTIES TO THIS NOTE AND ADDITIONAL INDORSERS, GUARANTORS OR SURETIES MAY
BE ADDED WITHOUT NOTICE AND WITHOUT AFFECTING THE LIABILITY OF THE ORIGINAL
MAKER OR ANY ORIGINAL INDORSER, SURETY OR GUARANTOR.

     Section 8. Commercial Loan. The Loan is made for the purpose of carrying on
a business or commercial activity or acquiring real or personal property as an
investment or carrying on an investment activity and not for personal or
household purposes.

     Section 9. Usury Limitations. Borrower and Lender intend to comply with all
Laws with respect to the charging and receiving of interest. Any amounts charged
or received by Lender for the use or forbearance of the Principal to the extent
permitted by Law, will be amortized and spread throughout the Term until payment
in full so that the rate or amount of interest charged or received by Lender on
account the Principal does not exceed the Maximum Interest Rate. If any amount
charged or received under the Loan Documents that is deemed to be interest is
determined to be in excess of the amount permitted to be charged or received at
the Maximum Interest Rate, the excess will be deemed to be a prepayment of
Principal when paid, without premium, and any portion of the excess not capable
of being so applied will be refunded to Borrower. If during the Term the Maximum
Interest Rate, if any, is eliminated, then for purposes of the Loan, there will
be no Maximum Interest Rate.

     Section 10. Applicable Law. This Note is governed by and will be construed
in accordance with the Laws of the State of Colorado, without regard to conflict
of law provisions.

     Section 11. Time of the Essence. Time is of the essence with respect to the
payment and performance of the Obligations.

     Section 12. Cross-Default. A default under any other note now or hereafter
secured by the Loan Documents or under any loan document related to such other
note constitutes a default under this Note and under the other Loan Documents.
When the default under the other

                                       4

<PAGE>

note constitutes an Event of Default under that note or the related loan
document, an Event of Default also will exist under this Note and the other Loan
Documents.

     Section 13. Construction. Unless expressly provided otherwise in this Note,
this Note will be construed in accordance with the Exhibit attached to the Deed
of Trust entitled "Rules of Construction."

     Section 14. Deed of Trust Provisions Incorporated. To the extent not
otherwise set forth in this Note, the provisions of the Articles of the Deed of
Trust entitled "Expenses and Duty to Defend," "Waivers," "Notices," and
"Miscellaneous" are applicable to this Note and deemed incorporated by reference
as if set forth at length in this Note.

     Section 15. Joint and Several Liability; Successors and Assigns. If Maker
consists of more than one entity, the obligations and liabilities of each such
entity will be joint and several. Without limiting the generality of the
foregoing, all entities constituting Borrower waive any rights which they might
otherwise have under Section 13-50-02 or Section 13-50-103, Colorado Revised
Statutes (or under any corresponding future statute) by reason of any release of
fewer than all of the parties constituting Borrower. This Note binds Borrower
and successors, assigns, heirs, administrators, executors, agents and
representatives and inures to the benefit of Lender and its successors, assigns,
heirs, administrators, executors, agents and representatives.

     Section 16. Absolute Obligation. Except for the Section of this Note
entitled "Limitation of Liability," no reference in this Note to the other Loan
Documents and no other provision of this Note or of the other Loan Documents
will impair or alter the obligation of Borrower, which is absolute and
unconditional, to pay the Principal, interest at the Fixed Interest Rate and any
other amounts due and payable under this Note, as and when required.

          IN WITNESS WHEREOF, Borrower has executed and delivered this Note as
of the date first set forth above.

                                              AMERIVEST KELLOGG INC., a Colorado
                                              corporation

                                              By: John B. Greenman
                                                  ------------------------------
                                              Name: John B. Greenman
                                              Title: Vice President

                                       5<PAGE>

                                                                Exhibit 10.21(d)

                                                        TIAA Appl. #AAA1280
                                                        TIAA Mtge. # M - 0005296

                                 PROMISSORY NOTE

$10,100,000.00                                          Denver, Colorado
                                                        Dated: December 23, 2002

          FOR VALUE RECEIVED, AMERIVEST SHERIDAN CENTER INC., a Colorado
corporation ("Borrower") having its principal place of business at 1780 S.
Bellaire Street, Suite 515, Denver, Colorado 80222, promises to pay to TEACHERS
INSURANCE AND ANNUITY ASSOCIATION OF AMERICA ("Lender"), a New York corporation,
or order, at Lender's offices at 730 Third Avenue, New York, New York 10017 or
at such other place as Lender designates in writing, the principal sum of TEN
MILLION, ONE HUNDRED THOUSAND AND NO/100s DOLLARS ($10,100,000.00) (the
principal sum or so much of the principal sum as may be advanced and outstanding
from time to time, the "Principal"), in lawful money of the United States of
America, with interest on the Principal from the date of this Promissory Note
(this "Note") through and including January 1, 2013 (the "Maturity Date") at the
fixed rate of seven and four tenths percent (7.40%) per annum (the "Fixed
Interest Rate").

          This Note is secured by, among other things, the Deed of Trust,
Assignment of Leases and Rents, Security Agreement, and Fixture Filing Statement
(the "Deed of Trust") dated the date of this Note made by Borrower for the
benefit of Lender as security for the Loan. All capitalized terms not expressly
defined in this Note will have the definitions set forth in the Deed of Trust.

     Section 1. Payments of Principal and Fixed Interest.

          a. Borrower will make monthly installment payments ("Debt Service
Payments") as follows:

               (i) On January 1, 2003, a payment of accrued interest on the
     Principal at the Fixed Interest Rate; and

               (ii) On February 1, 2003 and on the first day of each succeeding
     calendar month through and including January 1, 2013, payments in the
     amount of Seventy-Three Thousand Nine Hundred Eighty-Two Dollars and Fifty
     Cents ($73,982.50), each of which will be applied first to interest on the
     Principal at the Fixed Interest Rate and then to the Principal.

          b. On the Maturity Date, Borrower will pay the Principal in full
together with accrued interest at the Fixed Interest Rate and all other amounts
due under the Loan Documents.

     Section 2. Prepayment Provisions.

          a. The following definitions apply:

          "Discount Rate" means the yield on a U.S. Treasury issue selected by
Lender, as published in the Wall Street Journal, two weeks prior to prepayment,
having a maturity date

                                       1

<PAGE>

corresponding (or most closely corresponding, if not identical) to the Maturity
Date, and, if applicable, a coupon rate corresponding (or most closely
corresponding, if not identical) to the Fixed Interest Rate.

          "Default Discount Rate" means the Discount Rate less 300 basis points.

          "Discounted Value" means the Discounted Value of a Note Payment based
on the following formula:

              NP
          (1 + R/12)n  =  Discounted Value

          NP       =      Amount of Note Payment

          R        =      Discount Rate or Default Discount Rate as the case may
                          be.

          n        =      The number of months between the date of
                          prepayment and the scheduled date of the
                          Note Payment being discounted rounded to the
                          nearest integer.

          "Note Payments" means (i) the scheduled Debt Service Payments for the
period from the date of prepayment through the Maturity Date and (ii) the
scheduled repayment of Principal, if any, on the Maturity Date.

          "Prepayment Date Principal" means the Principal on the date of
prepayment.

          b. This Note may not be prepaid in full or in part before January 1,
2008. Commencing on January 1, 2008, provided there is no Event of Default,
Borrower may prepay this Note in full, but not in part, on the first day of any
calendar month, upon 60 days prior notice to Lender and upon payment in full of
the Debt which will include a payment (the "Prepayment Premium") equal to the
greater of (i) an amount equal to the product of 1% times the Prepayment Date
Principal and (ii) the amount by which the sum of the Discounted Values of Note
Payments, calculated at the Discount Rate, exceeds the Prepayment Date
Principal. Provided there is no Event of Default, this Note may be prepaid in
full without payment of the Prepayment Premium during the last 90 days of the
Term. This Note may not be prepaid without simultaneous prepayment in full of
any other notes secured by the Loan Documents. Notwithstanding the foregoing,
this Note may be prepaid in part in accordance with Section 4 of the
Cross-Collateralization and Cross-Default Agreement of even date herewith under
the circumstances set forth therein.

          c. After an Event of Default or upon any prepayment not permitted by
the Loan Documents, any tender of payment of the amount necessary to satisfy all
or any part of the Debt, any decree of foreclosure, any statement of the amount
due at the time of foreclosure (including foreclosure by power of sale) and any
tender of payment during any redemption period after foreclosure, will include
an amount (the "Evasion Premium") equal to the greater of (i) an amount equal to
the product of 1% plus 300 basis points times the Prepayment Date Principal, and
(ii) the amount by which the sum of the Discounted Values of the Note Payments,
calculated at the Default Discount Rate, exceeds the Prepayment Date Principal.

                                       2

<PAGE>

          d. Borrower acknowledges that:

               (i) a prepayment will cause damage to Lender;

               (ii) the Evasion Premium is intended to compensate Lender for the
     loss of its investment and the expense incurred and time and effort
     associated with making the Loan, which will not be fully repaid if the Loan
     is prepaid;

               (iii) it will be extremely difficult and impractical to ascertain
     the extent of Lender's damages caused by a prepayment after an Event of
     Default or any other prepayment not permitted by the Loan Documents; and

               (iv) the Evasion Premium represents Lender and Borrower's
     reasonable estimate of Lender's damages for the prepayment and is not a
     penalty.

     Section 3. Events of Default:

          a. It is an "Event of Default" under this Note:

               (i) if Borrower fails to pay any amount due, as and when
     required, under this Note or any other Loan Document and the failure
     continues for a period of 5 days; or

               (ii) if an Event of Default occurs under any other Loan Document.

          b. If an Event of Default occurs, Lender may declare all or any
portion of the Debt immediately due and payable ("Acceleration") and exercise
any of the other Remedies.

     Section 4. Default Rate. Interest on the Principal will accrue at the
Default Interest Rate from the date an Event of Default occurs.

     Section 5. Late Charges.

          a. If Borrower fails to pay any Debt Service Payment when due and the
failure continues for a period of 5 days or more or fails to pay any amount due
under the Loan Documents on the Maturity Date, Borrower agrees to pay to Lender
an amount (a "Late Charge") equal to five cents ($.05) for each one dollar
($1.00) of the delinquent payment.

          b. Borrower acknowledges that:

               (i) a delinquent payment will cause damage to Lender;

               (ii) the Late Charge is intended to compensate Lender for loss of
     use of the delinquent payment and the expense incurred and time and effort
     associated with recovering the delinquent payment;

               (iii) it will be extremely difficult and impractical to ascertain
     the extent of Lender's damages caused by the delinquency; and

                                       3

<PAGE>

               (iv) the Late Charge represents Lender and Borrower's reasonable
     estimate of Lender's damages from the delinquency and is not a penalty.

     Section 6. Limitation of Liability. This Note is subject to the limitations
on liability set forth in the Article of the Deed of Trust entitled "Limitation
of Liability."

     Section 7. WAIVERS. IN ADDITION TO THE WAIVERS SET FORTH IN THE ARTICLE OF
THE DEED OF TRUST ENTITLED "WAIVERS," BORROWER WAIVES PRESENTMENT FOR PAYMENT,
DEMAND, DISHONOR AND, EXCEPT AS EXPRESSLY SET FORTH IN THE LOAN DOCUMENTS,
NOTICE OF ANY OF THE FOREGOING. BORROWER FURTHER WAIVES ANY PROTEST, LACK OF
DILIGENCE OR DELAY IN COLLECTION OF THE DEBT OR ENFORCEMENT OF THE LOAN
DOCUMENTS. BORROWER AND ALL INDORSERS, SURETIES AND GUARANTORS OF THE
OBLIGATIONS CONSENT TO ANY EXTENSIONS OF TIME, RENEWALS, WAIVERS AND
MODIFICATIONS THAT LENDER MAY GRANT WITH RESPECT TO THE OBLIGATIONS AND TO THE
RELEASE OF ANY SECURITY FOR THIS NOTE AND AGREE THAT ADDITIONAL MAKERS MAY
BECOME PARTIES TO THIS NOTE AND ADDITIONAL INDORSERS, GUARANTORS OR SURETIES MAY
BE ADDED WITHOUT NOTICE AND WITHOUT AFFECTING THE LIABILITY OF THE ORIGINAL
MAKER OR ANY ORIGINAL INDORSER, SURETY OR GUARANTOR.

     Section 8. Commercial Loan. The Loan is made for the purpose of carrying on
a business or commercial activity or acquiring real or personal property as an
investment or carrying on an investment activity and not for personal or
household purposes.

     Section 9. Usury Limitations. Borrower and Lender intend to comply with all
Laws with respect to the charging and receiving of interest. Any amounts charged
or received by Lender for the use or forbearance of the Principal to the extent
permitted by Law, will be amortized and spread throughout the Term until payment
in full so that the rate or amount of interest charged or received by Lender on
account the Principal does not exceed the Maximum Interest Rate. If any amount
charged or received under the Loan Documents that is deemed to be interest is
determined to be in excess of the amount permitted to be charged or received at
the Maximum Interest Rate, the excess will be deemed to be a prepayment of
Principal when paid, without premium, and any portion of the excess not capable
of being so applied will be refunded to Borrower. If during the Term the Maximum
Interest Rate, if any, is eliminated, then for purposes of the Loan, there will
be no Maximum Interest Rate.

     Section 10. Applicable Law. This Note is governed by and will be construed
in accordance with the Laws of the State of Colorado, without regard to conflict
of law provisions.

     Section 11. Time of the Essence. Time is of the essence with respect to the
payment and performance of the Obligations.

     Section 12. Cross-Default. A default under any other note now or hereafter
secured by the Loan Documents or under any loan document related to such other
note constitutes a default under this Note and under the other Loan Documents.
When the default under the other

                                       4

<PAGE>

note constitutes an Event of Default under that note or the related loan
document, an Event of Default also will exist under this Note and the other Loan
Documents.

     Section 13. Construction. Unless expressly provided otherwise in this Note,
this Note will be construed in accordance with the Exhibit attached to the Deed
of Trust entitled "Rules of Construction."

     Section 14. Deed of Trust Provisions Incorporated. To the extent not
otherwise set forth in this Note, the provisions of the Articles of the Deed of
Trust entitled "Expenses and Duty to Defend," "Waivers," "Notices," and
"Miscellaneous" are applicable to this Note and deemed incorporated by reference
as if set forth at length in this Note.

     Section 15. Joint and Several Liability; Successors and Assigns. If Maker
consists of more than one entity, the obligations and liabilities of each such
entity will be joint and several. Without limiting the generality of the
foregoing, all entities constituting Borrower waive any rights which they might
otherwise have under Section 13-50-02 or Section 13-50-103, Colorado Revised
Statutes (or under any corresponding future statute) by reason of any release of
fewer than all of the parties constituting Borrower. This Note binds Borrower
and successors, assigns, heirs, administrators, executors, agents and
representatives and inures to the benefit of Lender and its successors, assigns,
heirs, administrators, executors, agents and representatives.

     Section 16. Absolute Obligation. Except for the Section of this Note
entitled "Limitation of Liability," no reference in this Note to the other Loan
Documents and no other provision of this Note or of the other Loan Documents
will impair or alter the obligation of Borrower, which is absolute and
unconditional, to pay the Principal, interest at the Fixed Interest Rate and any
other amounts due and payable under this Note, as and when required.

          IN WITNESS WHEREOF, Borrower has executed and delivered this Note as
of the date first set forth above.

                                               AMERIVEST SHERIDAN CENTER INC., a
                                               Colorado corporation

                                               By: John B. Greenman
                                                   -----------------------------
                                               Name: John B. Greenman
                                               Title: Vice President

                                       5

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