Alongside
Edward, Lemieux was among the earliest researchers studying
negative hyperconjugation (i.e., the anomeric effect) or the preference
for gauche conformations about the C1–O5 bond in carbohydrates.
Lemieux also studied an esoteric, if not controversial, theory known
as the reverse anomeric effect (RAE). This theory is used to rationalize
scenarios where predicted anomeric stabilization does not occur. One
such example is the Kochetkov amination where reducing end amines
exist solely as the β-anomer. Herein, we provide a brief account
of Lemieux’s contributions to the field of stereoelectronics
and apply this knowledge toward the synthesis of β-amino human
milk oligosaccharides (βΑ-HMOs). These molecules were
evaluated for their ability to inhibit growth and biofilm production
in Group B Streptococcus (GBS) and Staphylococcus aureus. While the parent HMOs lacked antimicrobial and antibiofilm activity,
their β-amino derivatives significantly inhibited biofilm formation
in both species. Field emission gun-scanning single electron microscopy
(FEG-SEM) revealed that treatment with β-amino HMOs significantly
inhibits bacterial adherence and eliminates the ability of both microbes
to form biofilms.
Common carbohydrate protecting group reactions under continuous flow processes are reported in the context of producing partially-protected glucose building blocks from levoglucosan. Benzyl ether protection was demonstrated without the use of NaH using barium oxide, which, however, pointed to the need for forms of this catalyst not as susceptible to close packing under flow. Acylation conditions were developed under continuous flow in acetonitrile and avoiding pyridine. Ring-opening the derivatized levoglucosan with propanethiol was also demonstrated producing S-alkyl 2,4-di-O-benzyl-glucopyranoside building block in 2 rather than 12 steps in increased overall yield.
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