Q.13.67 - An Introduction to General, Organic, and Biological Chemistry

Question

What are the differences in the Fischer projections of D-galactose and L-galactose? (13.3)

Step-by-Step Solution

Answer

D-galactose is found in such sources as lactose (milk sugar), agar, gum arabic, sugar beets, seaweed, and nerve cell membranes. L-galactose is found in flaxseed mucilage, snail galactogen, agar, and other such sources. 

Step 1: Introduction

Gal-3 is a lectin that has been implicated of overexpression in metastatic cancers promoting cell migration and survival 

Step 2: Differences in the Fischer projections of D-galactose and L-galactose

• L-Galactose is the mirror image of D-galactose. In the Fischer projection of D-galactose, the -OH on carbon 2 and carbon 5 is on the right side, but on the left for carbon 3 and carbon 4 . 
• In L-galactose, the -OH groups are reversed; carbons 2 and 5 have $-\mathrm{OH}$  on the left, and carbons 3 and 4 have $-\mathrm{OH}$ on the right