Remote participation during glycosylation reactions of galactose building blocks: Direct evidence from cryogenic vibrational spectroscopy

The stereoselective formation of 1,2‐cis‐glycosidic bonds is challenging. However, 1,2‐cis‐selectivity can be induced by remote participation of C4 or C6 ester groups. Reactions involving remote participation are believed to proceed via a key ionic intermediate, the glycosyl cation. Although mechanistic pathways were postulated many years ago, the structure of the reaction intermediates remained elusive owing to their short‐lived nature. Herein, we unravel the structure of glycosyl cations involved in remote participation reactions via cryogenic vibrational spectroscopy and first principles theory. Acetyl groups at C4 ensure α‐selective galactosylations by forming a covalent bond to the anomeric carbon in dioxolenium‐type ions. Unexpectedly, also benzyl ether protecting groups can engage in remote participation and promote the stereoselective formation of 1,2‐cis‐glycosidic bonds

UK meteotsunamis: a revision and update on events and their frequency

A tsunami is a series of waves caused by the displacement of water. The displacement may result from ‘bottom‐up’ seabed movement, such as caused by earthquakes, landslides and volcanic eruptions or ‘top‐down’ movement, from pressure perturbations in the atmosphere. These ‘top‐down’ events are termed meteotsunamis. Meteotsunamis frequently occur in the Mediterranean, the Baltic Sea, the east coast and Great Lakes of North America, and Japan, so they are not exclusive to the United Kingdom. The most recent meteotsunami near the UK coast was in May 2017, when waves around 2m in elevation, generated by a storm passing over the UK, struck the coast of the Netherlands. Historical documents covering the past 150 years describe many meteotsunamis from United Kingdom (UK) coastal waters (Haslett et al ., 2009; Haslett and Bryant, 2009; Tappin et al ., 2013; Vilibić et al ., 2015; O'Brien et al ., 2018). Some of these events have resulted in fatalities, involving beach users who were struck by unexpected sea waves. Meteotsunamis commonly strike the coasts of the UK, damaging harbours, boats and very rarely, causing fatalities. In the UK, they were usually detected by analysis after the event, unless witnessed first‐hand. This post‐event analysis is particularly necessary in the UK because the data provided by the tide gauge system, operated by the Environment Agency, only records at 15‐min intervals, not in real time as in the rest of Europe. The periods of meteotsunamis are in the range of minutes to tens of minutes (Pattiaratchi and Wijeratne, 2015). A frequency of tens of minutes is similar to a typical frequency expected from a meteotsunami that would have an amplified response from harbour or bay resonance (Tappin et al ., 2013). Therefore, those occurring in UK waters are not often recorded with the present tide gauge settings and as a consequence, cannot be analysed effectively

Fernpartizipation in Glykosylierungen von Galaktose‐Bausteinen: Direktnachweis durch kryogene Schwingungsspektroskopie

Die stereoselektive Bildung von 1,2‐cis‐glykosidischen Bindungen ist bislang sehr anspruchsvoll. Häufig wird diese 1,2‐cis‐Selektivität durch Fernpartizipation (remote participation) von C4‐ oder C6‐Estergruppen herbeigeführt. Hierbei wird davon ausgegangen, dass ein ionisches Schlüsselintermediat, das Glykosylkation, gebildet wird. Obwohl derartige Mechanismen bereits vor Jahrzehnten postuliert wurden, konnte die exakte Struktur dieses Intermediats aufgrund seiner Kurzlebigkeit bisher nicht aufgeklärt werden. In dieser Studie nutzen wir kryogene Schwingungsspektroskopie und quantenchemische Rechnungen, um die Strukturen dieser Glykosylkationen aufzuklären. Acetylgruppen an der C4‐Position führen zur selektiven Bildung von α‐Galaktosiden, indem eine kovalente Bindung zum anomeren Kohlenstoff gebildet wird. Überraschenderweise können auch Benzylgruppen die stereoselektive Bildung von 1,2‐cis‐glykosidischen Bindungen durch Fernpartizipation herbeiführen