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D. J. BELL
Ri
R-2—C—O
R4
I \
/
R 3
C
XV6
(LV)
Ether
Ηδ
C—O
1
Vo-H
1/ \
C
H
I
(LVI)
Glycoside
In the ether, Ri-R 6 are either hydrogen or carbon whereas one of the
carbons (heavy type) in the glycoside is attached to two oxygen atoms,
and is, as has already been pointed out, the functional carbon of an
acetal system.
C. RING FORMATION IN BRANCHED-CHAIN MONOSACCHARIDES
Some special attention must be paid to the behavior of the branchedchain sugars when they form rings, as indeed they must do in their
natural environments, since they are found only in glycosidic combination, or as esters in the case of hamamelose.
Streptose (Section I, A, 6) can exist as a ring only in the furanose
form since there is no hydroxyl group available with which to form a
pyranose ring (Reaction 7).
CHO
1
H-C-OH
1
^C-C-OH
HO-C-H
CHo
HOH
(7)
Aldehydo-D-streptose
OH OH
a I β -D -Strep tof uranose
Hamamelose (Section I, A, 6), which occurs as the 2,5-digalloyl ester,
could be either in a furanose ring or open chain. The free sugar can
form either pyranose or furanose rings (Reaction 8).
CHO
R-CO-O-CH C-OH
H-C-OH
H-C-OH
CHoO-COR
CH 2 0.
1 /
K OH
R =
COR
0
\
-^
[
OH
OH
1
OH
► HOH
-CH 2 0
-OH
COR
(8)