October 9, 1956

Dear Joe:

Have you had a chance to give any thought to my proposal for the examination
of DAP-analogues? Bernie Davis has done som more work with the DAP-less mtant
(and I have too) and it is working out rather cleanly. When deprived of DAP in
a growth medium, the mitant lyses. This lysis oan be inhibited either by sucrose
(10%) or by deprivation of other growth factors, so there is a good basic
analogy with penicillin.

The compofind itself is not commerééally available, but it is accumlated
rather heavily by other lysine-dependent organisms, as Davis has shown. It
should not be an insuperable synthetic problem, on paper. But the main point
is whether analogues can be made which will compete with DAP incorpora tion
dn organisms that normally synthesize it; at least the sulfonic analogues
should be tried, or perhaps some amino-substituted forms.

Z realize this is a little out of the line of your current dpera tions,
but it dees look to me like a good bet for a rational chemotherapsutic. I haven't
discussed this with anyone else yet; if Bristol isn't going to be interested,
I ought to try to provoke someone else with 1t & will therefae wait to hear
from you.

Yours sinos rely.

Joshua Lederberg

Dr. J. Lein
Bristol Labs.
Syracuse N.Y.