Provide the answers to the following questions about quinine: a) Identify the stereochemical centres and state their absolute configurations. b) Explain the basis of accumulation and describe the ion

A chiral centre is a carbon atom bonded to four different groups. In the quinine structure, there are four such carbon atoms:

• The carbon atom bearing the hydroxyl (-OH) group.
• The carbon atom connecting the quinoline ring system to the quinuclidine ring system.
• The carbon atom at the bridgehead of the quinuclidine ring, which is bonded to the vinyl group.
• The carbon atom adjacent to the vinyl group within the quinuclidine ring.

The absolute configurations for natural quinine are:

• Carbon bearing the -OH group: (R)
• Carbon connecting the quinoline and quinuclidine systems: (S)
• Carbon at the bridgehead of the quinuclidine ring (bonded to vinyl group): (R)
• Carbon adjacent to the vinyl group within the quinuclidine ring: (S)

Quinolines, such as quinine, are weak bases. They accumulate in the acidic environment of the food vacuole within the malaria parasite (Plasmodium falciparum), which resides in red blood cells. The food vacuole has a significantly lower pH (approximately 5.0-5.5) compared to the surrounding cytoplasm (pH ~7.2) and blood plasma (pH ~7.4).

When quinine, in its un-ionized (lipid-soluble) form, enters the acidic food vacuole, its basic nitrogen atoms become protonated (ionized). The two basic nitrogen atoms are the quinoline nitrogen (within the aromatic ring system) and the quinuclidine nitrogen (within the bridged bicyclic ring system). The protonated, ionized form of quinine is water-soluble and cannot easily cross the lipid membrane of the food vacuole to exit. This