|
Showing 1 - 3 of
3 matches in All Departments
The chemistry of condensed tannins has hitherto represented a
relatively unattractive and therefore neglected area of study; one
in which the weight of research effort involved is invariably
disproportionate to the results achieved, in which the
participating schools generally confine their approach to specific
molecular species, and in which as yet no consensus has been
reached regarding likely precursors. The problems which beset those
engaged in this field represent a combined function of the abnormal
complexity of the gradational range of oligomers of increasing mass
and affinity for substrates which typify most extracts rich in
tannins, and the consequent problem of their isolation and
purification, the high chirality of tannin oligomers, the need to
contend with the phenomenon of dynamic 'rotational isomerism about
interflavanoid bonds in the IH n.m.r. spectral interpretation of
their derivatives, the lack of precise knowledge regarding the
points of bonding at nucleophilic centres, and the obvious
limitations of a hitherto predominantly analytical approach. The
last of these reflects the need for a general method of synthesis
which permits unambiguous proof of both structure and absolute
configuration also at higher oligomeric levels. With these
objectives in mind we initiated a purely synthetic approach based
on the premise that flavan-3,4-diols as source of electrophilic
flavanyl-4-carbocations, and flavan-3-0Is as nucleophiles (cf 1,2)
represent the prime initiators of a process of repetitive
condensation in which the immediate products also represent the
sequent nucleophilic substrates.
|
You may like...
Gloria
Sam Smith
CD
R238
R195
Discovery Miles 1 950
Loot
Nadine Gordimer
Paperback
(2)
R398
R330
Discovery Miles 3 300
Loot
Nadine Gordimer
Paperback
(2)
R398
R330
Discovery Miles 3 300
Loot
Nadine Gordimer
Paperback
(2)
R398
R330
Discovery Miles 3 300
|