Notes Weds: December 3, 2008
Today’s Feature: The Fischer Proof of D-Glucose (“E. Fischer was the greatest chemist of all time”). The following Fisher projections were developed in 1888, and the validity of these Fischer projections was confirmed in 1951.
The SUGAR TREE: Starting from the simplest carbohydrate, in the D-series, glyceraldehyde:
D-glyceraldehyde CHO OH
CH2OH
CHO CHO OH HO Tetroses OH OH
CHO CHO CHO CHO OH HO OH HO Pentoses OH OH HO HO OH OH OH OH
CH2OH CH2OH CH2OH CH2OH ribose arabinose xylose lyxose
CHO CHO CHO CHO CHO CHO CHO CHO OH HO OH HO OH HO OH HO OH OH HO HO OH OH HO HO Hexoses OH OH OH OH HO HO HO HO OH OH OH OH OH OH OH OH
CH2OH CH2OH CH2OH CH2OH CH2OH CH2OH CH2OH CH2OH allose altrose glucose mannose gulose idose galactose talose
Fischer proof of glucose:
2 3 4 6 1 CHO CHO CHO CHO 5 CHO CHO 7CHO 8 CHO OH HO OH HO OH HO OH HO OH OH HO HO OH OH HO HO OH OH OH OH HO HO HO HO OH OH OH OH OH OH OH OH
CH2OH CH2OH CH2OH CH2OH CH2OH CH2OH CH2OH CH2OH allose altrose glucose mannose gulose idose galactose talose
1.) CHO CO2H
HNO3
OH OH
CH2OH CO2H glucose an aldaric acid (an aldose) optically active! Based on this, structures (1) and (7) can be excluded
2 3 4 6 1 CHO CHO CHO CHO 5 CHO CHO 7CHO 8 CHO OH HO OH HO OH HO OH HO OH OH HO HO OH OH HO HO OH OH OH OH HO HO HO HO OH OH OH OH OH OH OH OH
CH2OH CH2OH CH2OH CH2OH CH2OH CH2OH CH2OH CH2OH allose altrose glucose mannose gulose idose galactose talose
2.) CHO CO2H CHO CO2H Br2, H2O Ruff degradation HNO3 1) Ca(OH)2 OH OH 2) Fe2(SO4)3, H2O2 OH OH (-CO2) CH2OH CH2OH CH2OH CO2H glucose an aldonic acid pentose optically active! Based on this, structures (2), (5) and (6) can be excluded. 2 3 4 6 1 CHO CHO CHO CHO 5 CHO CHO 7CHO 8 CHO OH HO OH HO OH HO OH HO OH OH HO HO OH OH HO HO OH OH OH OH HO HO HO HO OH OH OH OH OH OH OH OH
CH2OH CH2OH CH2OH CH2OH CH2OH CH2OH CH2OH CH2OH allose altrose glucose mannose gulose idose galactose talose
3) CN CO H CHO CO H Fisher-Kiliani 2 2 CHO synthesis 1) HCN 2) Ba(OH) 3) Na/Hg HNO3 2x 2x pH 3-5 2x 2x OH OH OH OH OH
CH2OH CH2OH CH2OH CH2OH CO2H arabinose both diastereomers Both optically active!
Based on this, structure (8) can be excluded because the aldaric acid derived from (7) (the other lyxose derivative) is not optically active.
2 3 4 6 1 CHO CHO CHO CHO 5 CHO CHO 7CHO 8 CHO OH HO OH HO OH HO OH HO OH OH HO HO OH OH HO HO OH OH OH OH HO HO HO HO OH OH OH OH OH OH OH OH
CH2OH CH2OH CH2OH CH2OH CH2OH CH2OH CH2OH CH2OH allose altrose glucose mannose gulose idose galactose talose
4) CO2H CO2H CH2OH HOHC O HOHC HO Na/Hg O O CO2H O O CH2OH pH > 5 O CHOH OH CHOH OH
CO2H glucaric acid CHO
separation 2x OH
CH2OH 2 different aldoses! Based on this, structure (4) can be excluded. If glucose had the structure of (4), only one aldose would be recovered because of its C2 symmetry… therefore (4) can be eliminated and the structure of GLUCOSE is firmly established as (3)!!! 2 3 4 6 1 CHO CHO CHO CHO 5 CHO CHO 7CHO 8 CHO OH HO OH HO OH HO OH HO OH OH HO HO OH OH HO HO OH OH OH OH HO HO HO HO OH OH OH OH OH OH OH OH
CH2OH CH2OH CH2OH CH2OH CH2OH CH2OH CH2OH CH2OH allose altrose glucose mannose gulose idose galactose talose