Competing C-4 and C-5-Acyl Stabilization of Uronic Acid Glycosyl Cations.

Uronic acids are carbohydrates carrying a terminal carboxylic acid and have a unique reactivity in stereoselective glycosylation reactions. Herein, the competing intramolecular stabilization of uronic acid cations by the C-5 carboxylic acid or the C-4 acetyl group was studied with infrared ion spectroscopy (IRIS). IRIS reveals that a mixture of bridged ions is formed, in which the mixture is driven towards the C-1,C-5 dioxolanium ion when the C-5,C-2-relationship is cis, and towards the formation of the C-1,C-4 dioxepanium ion when this relation is trans. Isomer-population analysis and interconversion barrier computations show that the two bridged structures are not in dynamic equilibrium and that their ratio parallels the density functional theory computed stability of the structures. These studies reveal how the intrinsic interplay of the different functional groups influences the formation of the different regioisomeric products.

A Guide to Doppler Ultrasound Analysis of the Face in Cosmetic Medicine. Part 1: Standard Positions.

Interest in Doppler ultrasound (DUS) analysis of the face has grown in cosmetic medicine, in particular for injectable fillers. When dealing with complications, DUS has the advantage of easily visualizing the filler and identifying the problem in relation to the patient's anatomy. When working with hyaluronic acid filler, ultrasound-guided injections with hyaluronidase can precisely target the problem. In addition, DUS can be used to study the anatomy of a patient, specifically to prevent intravascular injections. We predict that in a few years' time DUS will become standard equipment in the offices of cosmetic doctors. We discuss the basics of ultrasound imaging of different tissues with the concomitant terminology. With the use of 7 basic DUS probe positions, key anatomic reference points can be easily found. From these, all relevant anatomic structures in the face can be observed and analyzed. With some practice, physicians will ultimately be able to acquire a complete 3-dimensional mental image of a patient's face.

A Guide to Doppler Ultrasound Analysis of the Face in Cosmetic Medicine. Part 2: Vascular Mapping.

Duplex mode ultrasound imaging can detect the course of the main vascular structures in the face, which are known to be subject to variation. Once duplex mapping has been performed, measures can be taken to prevent injection into an artery, thereby avoiding skin necrosis or, worse, vision loss. For this reason, in particular, we predict that in the coming years sonography will become standard equipment in the offices of cosmetic doctors. We discuss the basics of vascular imaging by Doppler ultrasound, both in normal and pathologic situations. Starting from the 7 basic positions for the ultrasound probe, all facial arteries relevant in cosmetic medicine can be found.

The Glycosylation Mechanisms of 6,3-Uronic Acid Lactones.

Uronic acids are important constituents of polysaccharides found on the cell membranes of different organisms. To prepare uronic-acid-containing oligosaccharides, uronic acid 6,3-lactones can be employed as they display a fixed conformation and a unique reactivity and stereoselectivity. Herein, we report a highly ß-selective and efficient mannosyl donor based on C-4 acetyl mannuronic acid 6,3-lactone donors. The mechanism of glycosylation is established using a combination of techniques, including infrared ion spectroscopy combined with quantum-chemical calculations and variable-temperature nuclear magnetic resonance (VT NMR) spectroscopy. The role of these intermediates in glycosylation is assayed by varying the activation protocol and acceptor nucleophilicity. The observed trends are analogous to the well-studied 4,6-benzylidene glycosides and may be used to guide the development of next-generation stereoselective glycosyl donors.