α and β again

The descriptors ‘α’ and ‘β’ are also used in carbohydrate nomenclature to specify configuration of cyclic monosaccharides [1, P-102.3.4.2.1]. You may remember that aldehydo-glucose, the open-chain form of glucose, has four chiral centres. Consider the structures (a) and (b):

(a)	(b)

aldehydo-D-gluco-hexose (carbohydrate) aldehydo-D-glucose (carbohydrate) (2R,3S,4R,5R)-2,3,4,5,6-pentahydroxyhexanal (substitutive) aldehydo-L-gluco-hexose (carbohydrate) aldehydo-L-glucose (carbohydrate) (2S,3R,4S,5S)-2,3,4,5,6-pentahydroxyhexanal (substitutive)

Upon cyclisation of either enantiomer, an extra chiral centre is created at the position 1. This centre is referred to as anomeric centre [2, 2-Carb-6.1] and two resulting stereoisomers are anomers. For example, cyclisation of aldehydo-D-glucose (a) brings about two major forms of D-glucose, (c) and (d):

(c)	(d)

α, β, ξ

Here’s a molecule everybody must have heard about: testosterone (a).

(a)

testosterone (INN) 17β-hydroxyandrost-4-en-3-one (fundamental parent + substitutive) (1S,3aS,3bR,9aR,9bS,11aS)-1-hydroxy-9a,11a-dimethyl-1,2,3,3a,3b,4,5,8,9,9a,9b,10,11,11a-tetradecahydro-7H-cyclopenta[a]phenanthren-7-one (fused ring + additive + substitutive)