“March 26, 1973

Dre. Hartmut: Braun oe
of. Dr. W. Litthe:

  

Organdach-Cherischea Institut der Universitat

 

Deaxi Drs; Braun,

. Lam.deeply euberrassed to have to tell you that your letteriof
Aprik,:26th 1972. was unfortuoately misieid. Please accept my contrite:
apologies and.I hope, that. we may. still be able to be of some gervice

o. you em which interests us‘ very much.»

to-youdin .response.to. your. problem

Our: programs. are written in the LISP language and it“ would: probably
berofsLittle benefit.to you to attempt ta operate them unless you have
an: expert who. is. familiar with this particular kind of computer soft- ..
wares In:our experience, unless we are dealing with a colleague who has
identical. equipment,.it would requite about one month's effort to understaue
and to. make minor revisions in the program to enable it to be run. on:
other computer systems. And I am afraid I have to tell you that we are
constantly up-dating and correcting the program which I am afraid to say
is also some discouragement. However, if you do have such 4 colleague
and he hag the means to be able to spend a few weeka with us, we will be
glad to give him all possible advice and guidance.

Alternatively we can attempt to run your problem on our system which
we would be very glad to do.

I have to tell you right away, however, that in its general form
it would simply not be practical to produce a complete list of all of the
isomers of CiQHi9- There are over 1,000 of the strictly A-cyclic isomers
and many more if one includes all of the possible cycles. I enclose a
brief diagram that illustrates the dimensions of the problem and I can
also-refer you to wy chapter in Waller's book "Biochemical Ap lications
of Mass Spectrometry", John Wiley & Sons, New York, pp.193-207, 1972.

“I can, however, enclose a set of diagrams of the trivaleat planar
graphs of orders from 0 to 10 which, indeed, must encompass the example,
Ci94y > with the following possible exceptions: (1) a quadrivaient center,
all cases of which are, however, also enumerated up to 8 vertices or (2) a
non-planar graph, for which there is not yet any precedent among \snall
molecules.

I will remind you that a vertex is a point of jumctore o-: two simple
rings so that the case where C108, must be mapped onto as many 45 10
yertices would represent a physically unrealizable degree of >ridging.

One can achieve the total enumeration of C19B10 cyclic molecules by mapping
additional carbon atoms onto the edges of the graphs of lower order.

-~2=
De. Haxtnat: Braun Re 3/26/73

st extensive, ‘and essentially trivial ,axample would be cyclodecane
‘10° carbong: would be. planted on. the single edge (1.e.. simple

  
  
  

che graph of vertex or Q. One would then also have to remove

suffictent, hydrogens, 1.e-. create ungaturations to match.the.empirical

 
  
   
  
  

"would. encourage. you. to experiment..briefly with these kinds ‘cf

ions so as ta familiarize yourself with the problem but I do
A: “dt is a proMitable way to spend one's time in working out:
ail cases! For this we indeed have some computer programs butxthey would
run for“a:very long timeiand have an essentially useless if very

. voluminous. output. without anticipating some of the criteria by: which:

not

    

one would intend to filter them. If you have given any thought‘to this
problem, it might be possible to incorporate: those criteria.into.the
program,; #0 that one indeed would be able to. generate 4 usefully >
restricted: list of th ygaibilities that have net yet bean discriminated.

For exauple, it should be posaible to get. some idea of the total number

of double bonds in a particular molecule by observing the results.of
exhaustive hydrogenation. But in any case.I think it would-be useful to
start a dialogue to discuss the strategies for solving this problem and
for this purpose we would be happy to provide help of the kind. that the
computer programs can give. I do promise that there will be a‘wuch shorter
interval prior to the next response!

  

For speed I am enclosing some of the material by first class air
mail and will forward some bulky successors by air parcel post.

Sincerely yours,

Joshua Lederberg
Professor of Genetics

JL/rr
Enclosure .

P.S. I guess I do have to send you all of the ten vertex figures now gince
diademane already contradicts my stacement that this group would be un-
buildable for Cjplj9. It must be very difficult to do this except vhere
there is a high order of symmetry and I am also beginning to think that
you may have to give serious consideration to non-planar structures.

I have not constructed diagrams for these but I think you can build them

yourself if you understand the code for the 13 examples listed. Diademan
itself corresponds to BDEBB.