Flow scheme

Hydrolysis/Reduction

BH4- -reduction

Acetylation

Reagents

• Trifluoroacetic acid (TFA), 0.5 or 2 M
• Methanol
• Borane-4-methylmorpholine complex
• Sodium borohydride, 0.25 M in 1 M NH₄OH
• Ammonia 1 M
• Acetic acid, 10% in methanol
• Acetic anhydride

Procedure

1. Reduction of the acid labile sugar. The sugar (1 equivalent) and morpholinoborane (10 eq.) in 0.5 M TFA is kept at 100° for 2h.
   E.g. 1 mg hexose (6 µmol) requires 7 mg morpholinoborane (60 µmol).
2. The solution is evaporated to dryness and after addition of methanol again evaporated to dryness.
3. Reduce with 0.3 mL fresh solution of NaBH₄ in NH₄OH for 30 min at 20°.
4. Quench with 0.5 mL 10% HOAc in MeOH, evaporate to dryness. Add 0.5 mL 10% HOAc in MeOH and evaporate to dryness. Repeat once or twice. Add 0.5 mL MeOH and evaporate to dryness. Repeat once or twice.
5. Acetylate with TFA/Ac₂O (0.2+0.2 mL) 10 min 100°.
6. Partition between dichloromethane and water.

Test substances, Standards