Document:

<PAGE>

                                                        SIC CODE /       /
                                                        R/E CODE   /   /

             [logo] MERCANTILE-SAFE DEPOSIT & TRUST COMPANY

                            REVOLVING NOTE
                             (Commercial)

$20,000,000.00                                      Date:  August 11, 1999
----------------------                                   ------------------
     In this Note, the Bank named above is hereinafter referred to as
"Bank." The Maker means each and all parties who sign below, whether one or
more than one, and their obligations hereunder are joint and several.

     On or before   August 11, 2001     , the Maker promises to pay to the
                   ----------------------
order of Bank $  20,000,000.00*********************************************
              -------------------------------------------------------------
(Twenty Million 00/100****************** U.S. Dollars), or so much thereof
-----------------------------------------
as Bank in its discretion has advanced or readvanced and is outstanding
hereunder (being herein called "Principal Sum"), with interest as stated
below on the Principal Sum.  Bank has established a revolving line of
credit for Maker from which Maker, subject to Bank's consent, may obtain one
or more loans from time to time, with the aggregate unpaid Principal Sum of
such loans actually advanced and remaining unpaid not to exceed the face
amount of this Note.  Advances and readvances hereunder remaining unpaid
from time to time shall bear interest each day until paid at a daily
periodic rate, calculated on the basis of a 360-day year, corresponding to
an annual percentage rate equal to N/A 50 basis points above the 90-day
                                  -----------------------------------------
Libor
---------------------------------------------------------------------------
(being herein called the "Index").  The daily periodic interest rate will
increase or decrease as the Index increases or decreases.  Where Bank's
Prime Rate is used as the Index, the "Prime Rate" is one of several rates
set by Bank from time to time as an interest rate base for borrowings.

Bank may lend at rates above and below the Prime Rate.  Interest shall be
due and payable  quarterly
                -----------------------------------------------------------
---------------------------------------------------------------------------.

     If Maker fails to pay any amount within 15 days after the date on
which it is due, Maker agrees to pay a late charge of the greater of $2.00
or 5% of the delinquent amount.  Additionally, any payment required to be
made hereunder (including any payment of interest and/or principal) which is
not made on the date that the same becomes due and payable shall continue
as an obligation of the Maker until it is fully paid, and the Maker agrees
in addition to pay, to the extent permitted by law, late interest thereon
at a fluctuating rate, adjusted daily, equal to the interest rate otherwise
applicable hereunder plus two and one-half percent (2-1/2%) per annum, such
late interest to accrue from the date such overdue payment became due and
payable until paid.  All payments will be applied in any manner we choose
except as otherwise required by applicable law.  Generally, payments are
applied first to interest due; second to principal due; third to late
charges; fourth to any remaining interest and finally to the remaining
principal.

     It is expressly stipulated and agreed that the loan evidenced by this
Note is a "commercial loan" as defined in the Commercial Law Article of the
Annotate Code of Maryland.

     Maker covenants to provide Bank such financial information as Bank
may request from time to time and authorizes Bank to make all inquiries it
deems necessary to verify the accuracy of the information provided, to
protect and maintain its assets in good condition and repair, free of all
liens and encumbrances, to keep its assets insured against loss by fire,
theft and other casualties as required by Bank in such amounts and by
carriers satisfactory to Bank, not to dispose of any assets except in the
ordinary course of business, and to pay all taxes and assessments when due.

     Advances and readvances hereunder may be prepaid in whole or in part.
The fact that the balance hereunder may be reduced to zero from time to
time will not affect the continuing validity of this Note, and the balance
may be increased to the face amount of the Note after such reductions to
zero.  Bank in its discretion may make an advance which causes the
principal balance to exceed the face amount of the Note and such excess
shall be paid by the Undersigned upon demand with interest as provided
above.

<PAGE>
     The Maker represents and warrants to the Bank that (a) the Maker is
duly organized and existing and is in good standing under the laws of the
State of Missouri and is duly licensed or qualified to do business in all
         --------
jurisdictions wherein the nature of its business or the character of its
properties requires such licensing or qualification; (b) the Maker has all
requisite power and authority to execute this Note and to make the
borrowings contemplated hereunder; (c) this Note is a legal, valid and
binding obligation of the Maker, enforceable in accordance with its terms;
(d) there are no actions, suits or proceedings pending or, to the knowledge
of the Maker, threatened against or affecting it which would prevent the
Maker from executing this Note and performing its obligations hereunder;
(e) the Maker's performance under this Note shall not violate its
organizational documents or any other material contract or material
instrument to which the Maker is a party or by which the Maker is bound;
and (f) since the date of any financial statements of the Maker provided to
the Bank, except as specifically disclosed to the Bank in writing, there
have been no material adverse changes in the condition, financial or
otherwise, of the Maker nor any changes in the operations of the Maker
except those occurring in the ordinary course of business.

     Each of the following events shall constitute a default hereunder:
(a) the breach of any representation in or the failure of any Obligor
(which term shall include each Maker, endorser, surety and guarantor of any
of the Liabilities) to perform any covenant or agreement under any of the
documents evidencing the Liabilities (which term shall include all obligations
under this Note, and any renewals, extensions or modifications thereof, and all
other obligations of any kind of Maker to Bank and to any other party to the
extent of Bank's interest therein, now or hereafter existing, including
liabilities to Bank of Maker as a member of any partnership or other group
and whether incurred by Maker as principal or otherwise); (b) the death,
default or incapacity of any Obligor; (c) the filing of any petition under
the Federal Bankruptcy Code or any similar Federal or state statute, by or
against any Obligor; (d) an application or the appointment of a receiver
for, the making of a general assignment for the benefit of creditors by, or
the insolvency of any Obligor; (e) commencement of any proceeding under any
Federal or state statute or rule providing for the relief of debtors,
composition of creditors, arrangement, reorganization, receivership
liquidation or any similar event by or against any Obligor; (f) the entry
of a judgment against any Obligor; (g) the issuing of any attachment or
garnishment, or the filing of any lien, against any property of any Obligor;
(h) the suspension by any Obligor of the transaction of such Obligor's
usual business; (i) the merger or consolidation of any corporate Obligor
with any other corporation or the transfer, disposition or encumbrance of
all or a substantial part of the assets of any Obligor; (j) if any Obligor
misinformed or failed to inform Bank as to any matter which the Bank deems
material to a Liability; or (k) the determination by an officer of Bank
that an adverse change has occurred in the financial condition of any
Obligor from the condition of such Obligor as heretofore most recently
disclosed to Bank by a financial statement or in any other manner.  If this
Note is payable upon demand, demand may be made whether or not an event of
default has occurred.

     To secure payment of the Liabilities, Bank is hereby granted a lien
and security interest in all property of any Obligor held now or hereafter
by Bank in any capacity and upon the occurrence of any default hereunder
Bank shall have the right, immediately and without further action by it to
set-off against any of the Liabilities, all such property, and Bank shall
be deemed to have exercised such right of set-off and to have made a charge
against such property immediately upon the occurrence of such default even
though such charge is made or entered subsequently on the books of Bank.

     A delay by Bank in exercising any right or remedy shall not
constitute a waiver.  A waiver of a default, right or remedy shall not
constitute a waiver of a subsequent default, right or remedy.  A single or
partial exercise of a right or remedy shall not preclude or constitute a
waiver of any unexercised right or remedy.  Bank will not waive a default
by accepting partial payment of any amount due.  All rights and remedies
hereunder and under applicable laws shall be cumulative.  Every obligation
of each Obligor is joint and several.  Bank may exercise its rights against
any collateral or Obligor without first having recourse against any other
collateral or Obligor.

     Whenever any Obligor shall be in default hereunder, Bank at its
option (1) may cure the default at Maker's expense; (2) may refuse to make
further advances; (3) may declare any of the Liabilities immediately due
and payable; and (4) may exercise any or all rights and remedies available
to it under the documents evidencing the Liabilities and applicable law.

     Maker covenants to pay on demand, with interest until paid in full at
the rate imposed upon principal therein, all expenses incurred by Bank,
including legal fees, to cure any default herein, to enforce any provision
of the Liabilities or to exercise any right or remedy.

     Each Obligor waives presentment, notice of dishonor, protest and all
other demands and notices in connection with any of the Liabilities and
with respect to any collateral and waives any right to trial by jury and
further agrees that the courts of the State of Maryland shall have personal
jurisdiction over it in any legal proceedings with respect to any of the
Liabilities.  Each Obligor without further notice assents to all
extensions of the time of payment of any Liability or any other indulgence
or modification of a Liability, to any substitution, exchange or release of
collateral and to the addition or release of any Obligor, whether or not
done for consideration, all without in any way affecting its obligation.
Bank may unjustifiably and without reservation of rights impair any
Obligor's recourse against another Obligor or collateral.  Except when
invalid or unenforceable by statute or otherwise, each and every Obligor
authorizes any attorney designated by Bank to confess judgment in any Court
of Record and authorizes Bank to instruct the clerk of any Court of Record
to confess judgment against such Obligor at any time after this Note is due
by its terms or upon default, for the unpaid balance of this Note and
interest payable thereon, together with court costs and all other

<PAGE>
<PAGE>

amounts payable to Bank pursuant hereto, including attorneys' fees of 20%
of the total sum due, provided,  however, that any lien arising from such
confession of judgment shall not without further proceedings, apply or
attach to any real property as described in section 12-401 (i) of the
Maryland Commercial Law Article as the same may be amended from time to
time unless this is a loan to a corporation or a commercial loan in excess
of $75,000.00.

     The Undersigned hereby authorizes the Bank to accept instructions by
telephone from any Maker or a duly authorized representative of any Maker
to make advances or receive a repayment hereunder.  All advances made
hereunder shall be credited to the Maker's deposit account with the Bank.
The Maker agrees that the actual crediting of the sum of money so borrowed
to the Maker's deposit account shall constitute conclusive evidence that
the advance was made, and the failure of the Bank to forward to the Maker
an advice of credit shall not affect the obligation of the Maker to repay
such advance.

     This Note contains the full agreement of the parties and may be
modified only by a writing executed by the party to be charged.

     This Note is executed and delivered the date above written as an
instrument under Seal, specifically intending it to be a specialty and shall
be governed by the Laws of the State of Maryland, including without
limitation Title 12, Subtitle 1 of the Maryland Commercial Law Article.

     Notwithstanding anything in this Note to the contrary, if the Maker is
an individual and the original principal amount of the loan evidenced hereby
is not more than $15,000 ($75,000 if secured by owner-occupied, 1-4 family
residential real estate), then such loan shall be governed by Title 12,
Subtitle 9 of the Maryland Commercial Law Article.  In such event; (a) the
index shall be a rate or index external to the Bank as the Bank selects;
(b) interest shall be computed on the basis of a 365- rather than a 360-day
year; (c) the default rate of interest provided for herein shall not apply;
and (d) the confession of judgment provision contained herein shall not
apply.

CORPORATIONS OR PARTNERSHIPS SIGN BELOW      INDIVIDUALS SIGN BELOW

Mississippi Valley Bancshares, Inc.                                  (SEAL)
---------------------------------------      ------------------------------
Name of Corporation or Partnership

By  /s/ Andrew N. Baur           (SEAL)                              (SEAL)
  -------------------------------------      ------------------------------
          Chairman

By                               (SEAL)                              (SEAL)
  -------------------------------------      ------------------------------

                            GUARANTY

     In consideration of the loan or forebearance evidenced by the
foregoing Note, the undersigned (jointly and severally) absolutely and
unconditionally guarantees to Bank and every subsequent holder of the Note
(irrespective of its genuineness, validity, regularity or enforceability or
any other circumstance) the prompt payment (not merely the collection) of
the Note when due, according to its terms, which are incorporated herein,
and as they may be modified subsequently by any extension or renewal, in
whole or in part, any change in the interest rate or other term, or the
exchange, assignment, extension, waiver, modification or surrender of any
related right or security; and Bank and every subsequent holder of the
Note at its option may proceed in the first instance against the
undersigned to collect any obligation covered by this Guaranty, without
first proceeding against any collateral or other Obligor.

     Any debt of any Maker to the undersigned, now or hereafter existing,
is and shall be subordinated to the indebtedness and liability herein
guaranteed.  The undersigned agrees not to assert any right, directly or by
subrogation, against any Maker or any assets securing payment of the
indebtedness or liability herein guaranteed, so long as the debt evidenced
by the foregoing Note is outstanding.

     This Guaranty is Executed and delivered on the date of the foregoing
Note under Seal and specifically intending this to be a specialty, governed
by the laws of the State of Maryland.

CORPORATIONS OR PARTNERSHIPS SIGN BELOW     INDIVIDUALS SIGN BELOW

                                                                     (SEAL)
---------------------------------------     -------------------------------
Name of Corporation or Partnership

By                               (SEAL)                              (SEAL)
  -------------------------------------     -------------------------------

By                               (SEAL)                              (SEAL)
  -------------------------------------     -------------------------------EXHIBIT 4.1
                                                                     -----------

                              NOTICE OF REDEMPTION

                                       OF

                                CLASS B WARRANTS

To the Holders of Outstanding
Class B Warrants of Vion Pharmaceuticals, Inc.

                  We hereby give notice that we are redeeming all of our
outstanding Class B warrants on April 27, 2000. We are exercising this right
pursuant to the terms of the warrant agreement dated as of August 14, 1995
governing our Class B warrants.

TERMS OF REDEMPTION; CESSATION OF RIGHTS

                  Redemption Date:          April 27, 2000

                  Redemption Price:         $.05 per Warrant

                  The right of our Class B warrant holders to exercise their
warrants to purchase shares of our common stock will terminate at 5:00 p.m. New
York time on April 26, 2000 (one day prior to the Redemption Date). After such
time, holders of Class B warrants will have no rights except to receive, upon
surrender of their warrants, the Redemption Price. The Redemption Price is
substantially less than either (i) the current market price of the shares of
common stock receivable upon exercise of the Class B warrants or (ii) the
current price that could be obtained upon the sale of the Class B warrants in
the open market.

REDEMPTION PROCEDURE

                  Payment of the amount to be received on redemption will be
made by us upon the presentation and surrender of the Class B warrants for
payment at any time on or after the Redemption Date. To surrender Class B
warrants for redemption, holders should deliver certificates representing their
Class B warrants to American Stock Transfer & Trust Company, our warrant agent,
at the following address:

                     American Stock Transfer & Trust Company
                           40 Wall Street - 46th Floor
                            New York, New York 10005
                            Telephone: (718) 921-8100

EXERCISE PROCEDURE (EXPIRES 5:00 P.M. NEW YORK TIME ON APRIL 26, 2000)

                  In lieu of surrendering the warrants for redemption, Class B
warrant holders may, at their option, exercise their warrants to purchase our
common stock. Each Class B warrant entitles the holder to purchase at a price of
$6.23 one share of common stock.

<PAGE>

                  The Class B warrants may be exercised by delivery of the Class
B warrant certificates to American Stock Transfer and Trust Company at the
address set forth above under "Redemption Procedure" accompanied by a bank or
certified check made payable to Vion Pharmaceuticals, Inc. for the full amount
of the Exercise Price ($6.23 for each warrant exercised). The subscription form
on the reverse side of each warrant must be completed in full and signed by the
warrant holder and the signature guaranteed by an eligible institution. The
method of delivery of the warrant certificates is at the option and risk of the
holder, but if mail is used, registered mail properly insured is suggested.

                  The warrant certificate and the payment of the Exercise Price
must be received by the warrant agent prior to 5:00 p.m. New York time on April
26, 2000. Warrants which are received after such date will not be exercised, but
will be redeemed. Provided that a notice of exercise and payment is received by
the warrant agent prior to 5:00 p.m. New York time on April 26, 2000,
broker-dealers shall have three business days to deliver warrant certificates to
the warrant agent.

                  ANY WARRANT RECEIVED WHICH IS NOT ACCOMPANIED BY PAYMENT OF
THE EXERCISE PRICE OR WHICH IS RECEIVED WITHOUT THE SUBSCRIPTION FORM HAVING
BEEN COMPLETED AND SIGNED WILL BE DEEMED TO HAVE BEEN DELIVERED FOR REDEMPTION,
AND NOT FOR EXERCISE.

SOLICITATION AGENT

                  Representatives of D.H. Blair Investment Banking Corp. ("D.H.
Blair") are available to assist holders in the exercise of their Class B
warrants. To receive such assistance, please contact David Nachamie at (212)
495-4105 or Martin A. Bell at (212) 495-4594. Pursuant to the terms of the
warrant agreement governing the Class B warrants, we must pay a 5% fee to D.H.
Blair for each Class B warrant that is exercised if the exercise is solicited by
D.H. Blair (a portion of this fee may be re-allowed by D.H. Blair to other
dealers who solicit the exercise).

INFORMATION AGENT

                  The Company has retained an information agent for the exercise
and/or redemption of the warrants. The information agent may be reached at:

                     Corporate Investor Communications, Inc.
                                111 Commerce Road
                           Carlstadt, New Jersey 07072
                            Telephone: 1-877-842-2409

<PAGE>

                                [VION LETTERHEAD]

                      IMPORTANT - IMMEDIATE ACTION REQUIRED

                                                                  March 27, 2000

Dear Class B Warrant Holder:

                  Vion Pharmaceuticals, Inc. has called for redemption of all of
its outstanding Class B warrants for cash at the redemption price of $.05 per
warrant on April 27, 2000. A copy of the Notice of Redemption, a Prospectus and
our 1998 Annual Report is enclosed.

                  We are entitled to redeem the Class B warrants because we have
satisfied the condition of redemption - namely, that the average closing price
of our common stock exceeded $9.80 for a period of 30 consecutive business days
ending within 15 days of the date of this notice. The Class B warrants are
exercisable at an exercise price of $6.23 for one share of common stock. After
5:00 p.m., New York time on April 26, 2000, the Class B warrants will no longer
be exercisable for shares of common stock and you will only have the right to
receive the redemption price.

                  We urge you to consider the following two alternatives to
redemption which are available to you and which may be more beneficial to you
than redemption:

1.       Exercise of the Class B warrants.

                  Each Class B warrant is exercisable at an exercise price of
$6.23 for one share of our common stock. The closing price of our common stock
as reported by the Nasdaq National Market ranged from a high of $29.00 to a low
of $13.88 during the period from February 11, 2000 through March 23, 2000.
Current market quotations are available from the Nasdaq National Market or your
broker.

2.       Sale of the Class B warrants in the open market.

                  The Class B warrants may be sold in the open market. The
closing price of our Class B warrants as reported by the Nasdaq SmallCap Market
ranged from a high of $22.88 to a low of $7.50 during the period from February
11, 2000 through March 23, 2000. You should consult your own broker as to the
procedure for selling your warrants and for current market quotations.

<PAGE>

                  The procedures for exercise and/or redemption of the warrants
are set forth in the accompanying Notice of Redemption.

                  Questions and requests for assistance should be directed to
our information agent, Corporate Investor Communications, Inc. at
1-877-842-2409.

                                                  Very truly yours,

                                                  VION PHARMACEUTICALS, INC.

                                                  /s/ Alan Kessman
                                                  -----------------------------
                                                  Alan Kessman
                                                  President and Chief Executive
                                                  Officer

Source: [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00004-of-00352.parquet"}, [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00004-of-00352.parquet"}]]