3 CARBOHYDRATE BIOGENESIS
One of the most vital aspects
of pharmacognosy which has gained paramunt importance and legitimate recognition
in the recent past is the intensive and extensive studies involving the various
biochemical pathways that has ultimately led to the production of ‘secondary
constituents’ invariably employed as ‘drugs’. This type of specific
and elaborated study is frequently termed as biogenesis or drug biosynthesis.
It is quite pertinent to mention here that as it is absolutely necessary
for a medicinal chemist to understand the intricacies of chemical synthesis of
a potent drug substance, such as:
naproxen, chloramphenicol etc.,
exactly in the same vein a pharmacognosist must possess a thorough knowledge of
the biogenesis of drugs of natural origin.
A Swiss chemist G. Trier, as
far back in 1912, not only predicted but also postulated that amino acids and
their corresponding derivatives invariably act as the precursors of relatively
complex naturally occurring alkaloids mostly used as potent therapeutic agents.
Interestingly, soonafter the second half of the twentieth century, there had
been a tremendous progress in the era of isotopically labelled
organic compounds that facilitated the affirmation as well as confirmation
of the earlier
speculated theories. With the
advent of most advanced knowledge in sciences it has been established that the
carbohydrate biogenesis usually takes place due to the Photosynthesis from
carbon dioxide (CO2) as the starting material occurring abundantly
both in all plants and in certain purple bacteria as depicted below:
Calvin and coworkers
established the various steps involved in the chemical reactions ultimately leading
to the overall Eq. (a). They have also shown that D-ribose-1,
5-diphosphate is the primary acceptor of CO2. However, the exact
mechanism of this particular step whereby CO2 gets assimilated has
been studied at length with radio labelled 14CO2 and Chiorella
(a fresh water algae).
Besides, the following Eq. (b)
evidently illustrates the distribution of radiocarbon originating from 14CO2
after completion of one full photosynthetic cycle:
From Eq. (b) it may be
inferred that a triose phosphate having the identified radiocarbon distribution
shall ultimately result after completing a single full cycle. It would most
logically lead to hexose phosphate which should invariably contain relatively
higher amounts of 14CO2 (i.e., radio labelled
carbon), till such time after a series of recycling slots, give rise to an even
distribution of radio active carbon spread over the entire hexose molecule.
Source: Pharmacognosy And Pharmacobiotechnology By Ashutosh Kar
Source: Pharmacognosy And Pharmacobiotechnology By Ashutosh Kar
0 Comment:
Post a Comment