Spectrum Prediction of Androstane-Derivatives
The C-13 NMR-spectra of androstane-derivatives allow easy determination
of cis/trans ring-junction of the A and B-ring of these systems. Characteristic
differencies at C-5, C-7, C-9 and C-19 can be found which will be shown
in the first slide.
The following two slides show the characteristic differences at the positions
C-5, C-7, C-9 and C-19 for 5-alpha-androstane and 5-beta-androstane, respectively.
In these two cases neural network technology was applied in order to show,
that the implementation of stereochemical information within CSEARCH is
very versatile and can be used identically with HOSE-code and neural network
From the table it can be seen, that the trends introduced by stereochemical
interactions can be reproduced very well, the size of the effects is a
little bit too small, showing that further training of the neural network
When ignoring the stereochemical information, meanvalues from both
alpha- AND beta-androstane-derivatives will be taken, simply showing
the relative numbers of entries belonging to the class of alpha-androstanes
and to the class of beta-androstanes, repectively. As the term meanvalues
tells you, are usually .
The calculation above has been performed without any stereochemical information;
the prediction for the D-ring carbons shows values at 25.2 / 21.7 and 39.6ppm
having fairly large expectation ranges. From the inspection of the distribution
function it can be seen, that there are a few inconcistently assigned reference
data within the database, therefore increasing the expectation ranges,
whereas the meanvalues are quite reasonable. When adding a substituent
at the A-ring (e.g. a methylgroup in position 3 as selected in the next
slide), the chemical shift values for the D-ring carbons should be unaffected
as shown below.
Inserting rather unusual substituents at positions 2 and 3, respectively,
the D-ring carbons are further unaffected, for C-2 and C-3 a value of 41.1ppm
derived from 575 entries of the database is predicted at the one-bonmd
level taking into account only the first within the HOSE-code scheme. From
this calculation no trend can be predicted about the bahaviour of C-2 and
C-3, for both of them the identical reference material has been selected,
showing a correct implementaion of the HOSE-code scheme and the lack of
data for this particular problem, despite a database holding 270,000 C-13
NMR-spectra has been used (the combined collections of University of Vienna,
SADTLER Research Laboratories and Chemical Concepts/SPECINFO).
Last update: 06-Apr-2001