RNA oligomers at atomic resolution containing 1‐methylpseudouridine, an essential building block of mRNA vaccines

All widely used mRNA vaccines against COVID‐19 contain in their sequence 1‐methylpseudouridine (m1Ψ) instead of uridine. In this publication, we report two high resolution crystal structures (at up to 1.01 and 1.32 Å, respectively) of one such double‐stranded 12‐mer RNA sequence crystallized in two crystal forms. The structures are compared with similar structures which do not contain this modification. Additionally, the X‐ray structure of 1‐methyl‐pseudouridine itself was determined

Steviamine, a new class of indolizidine alkaloid [(1R,2S,3R,5R,8aR)-3-hydroxy­meth­yl-5-methyl­octa­hydro­indolizine-1,2-diol hydro­bromide]

X-ray crystallographic analysis of the title hydro­bromide salt, C10H20N+·Br−, of (1R,2S,3R,5R,8aR)-3-hydroxy­meth­yl-5-methyl­octa­hydro­indolizine-1,2-diol defines the absolute and relative stereochemistry at the five chiral centres in steviamine, a new class of polyhydroxy­lated indolizidine alkaloid isolated from Stevia rebaudiana (Asteraceae) leaves. In the crystal structure, mol­ecules are linked by inter­molecular O—H⋯Br and N—H⋯Br hydrogen bonds, forming double chains around the twofold screw axes along the b-axis direction. Intra­molecular O—H⋯O inter­actions occur

Synthesis of mucin glycans from the protozoon parasite Trypanosoma cruzi

A short, blockwise, 2+2-glycosylation approach to the synthesis of a tetrasaccharide component of Trypanosoma cruzi mucin is reported. Despite the use of a 1,2-linked disaccharide donor, high yield (79%) and good stereocontrol (>10:1, β:α) were achieved in the key glycosylation step. Preliminary studies indicate that this branched tetrasaccharide can serve as a substrate for enzymatic sialylation by the parasite cell surface trans-sialidase

Iodine Promoted Glycosylation with Glycosyl Iodides: α-Glycoside Synthesis.

Glycosidation of fully acetylated glucopyranosyl iodide with methanol under the influence of iodine gave α-glucoside selectively. Use of less reactive acceptors led to the formation of α/β-mixtures. Glycosylations with fully benzoylated glucosyl iodide yielded β-glucosides only. In contrast, iodine-promoted glycosylation of serine and threonine with 2-azido-2-deoxy-glycosyl iodides, easily obtained in three steps, proceeded smoothly, resulting in only α-linked products in high yield in most cases

Contrasting reactivity of thioglucoside and selenoglucoside donors towards promoters: Implications for glycosylation stereocontrol

The stereochemical outcome of glycosylation reactions with model thioglycosides and selenoglycosides proved to be dependent on the source of promoter iodonium ion, with iodine giving different results to N-iodosuccinimide (NIS) alone or N-iodosuccinimide/trimethylsilyltrifluoromethanesulfonate (NIS/TMSOTf). In contrast to armed thioglycosides, which anomerise, and disarmed thioglycosides, which do not react, both armed and disarmed selenoglycosides give rise to the corresponding glycosyl iodides when reacted with iodine. Further, whilst the single electron transfer agent DDQ alone is an ineffective promoter, in combination with iodine it produces better acetonitrile-assisted β-stereoselectivity with both thioglycosides and selenoglycosides than does tris(4-bromophenyl)aminium hexachloroantimonate (BAHA)

From Solution Phase to “On-Column” Chemistry: Trichloroacetimidate-Based Glycosylation Promoted by Perchloric Acid—Silica.

HClO4 immobilized on silica is found to be an efficient promoter for glycosylation reactions using trichloroacetimidate donors. The reactions can be performed successfully in solution as well as on column

Synthesis of Fully Substituted Polyhydroxylated Pyrrolizidines via Cope-House Cyclization

Total synthesis of the proposed structure of (-)-hyacinthacine C(5) and its epimers at C6 and C7 is described. A key step of the synthesis was the construction of the bicyclic pyrrolizidine system by means of a nucleophilic addition of a dithiane to a cyclic nitrone followed by a Cope-House cyclization

Steviamine, a new indolizidine alkaloid from Stevia Rebaudiana

The novel iminosugar (1R,2S,3R,5R,8aR)-3-(hydroxymethyl)-5- methyloctahydroindolizine-1,2-diol (steviamine) was isolated from leaf material of Stevia rebaudiana and leaves and bulbs of Veltheimia capensis. This is the first report of an indolizidine iminosugar alkaloid from the Asteraceae and Hyacinthaceae. Steviamine may occur in some Stevia products and influence taste. © 2010 Phytochemical Society of Europe