C-glycosylation invented by Pr Lubineau’s team: a key-reaction for innovation in cosmetics - Carbohydrate Chemistry: Chemical and Biological Approaches - page 6

The nature of the base also has a very significant effect on the yield and
on the reaction time as shown in Table 2. We confirmed on the model
reaction using the 2,4-pentanedione that NaOH is the ablest base to
quantitatively yield the b-C-xylosyl product with a decreasing reaction
time at a lower temperature (50 1C).
To allow further structure-activity relationships studies, we chose to
enhance the structural diversity of this new class of C-glycosyl derivatives
by subjecting the keto C-glycosyl compound to further transformations.
For this objective, the reduced products 14-20 (mixture of diastereo-
isomers obtained, see list in Table 3) were synthesized after treatment
with aqueous sodium borohydride for the first batch at a laboratory
scale. 13
In order to respect the principles of green chemistry and avoid complex
procedure to remove borate salts, a catalytic hydrogenation was de-
veloped. Accordingly, Ru/C was used as catalyst as described in Scheme 6
on a model reaction based on the reduction of the keto C-xylose 14 then
confirming that the reduced C-xylosyl compound 18 is a 50/50 diaste-
reoisomer mixture.

Table 2 Effect of the base on the model reaction depicted in Scheme 6.

Entry Base Yield Time Temp.

A NaHCO 3 87% 18h 90 1C

B NaHCO 3 Mixture 1h 90 1C

C LiOH 56% 18h 90 1C

D NaOH 88% 18h 90 1C

E NaOH 90% 1h 90 1C

F NaOH 97% 45min 50 1C

HO CH 3

O CH 3

Lubineau

Ru/C

CH 3

O

O OH O

H 2 O

O

reaction

+

HO OH

HO OH HO OH

O

OH

OH OH

CH 3

18

D-xylose

Scheme 6

Table 3 Reduction products of the keto C-glycosyl derivatives by reaction with NaBH 4 .

Compound Starting sugar R Yield %

14 D -glucose Me 88

15 D -fucose Me 65

16 D -arabinose Me 90

17

D -lactose

Me 65

18

D -xylose

Me 98

19

L -fucose

Me 86

20

D -glucose

4-OMe-Ph 100