Hypervalent Iodine and Carbohydrates – A New Liaison

Abstract

Synthetic applications of hypervalent iodine reagents in the oxidation state +3 in relation to unsaturated carbohydrates are reviewed. By using the Koser reagent or its bis(azido) derivative, fully protected glycals are oxidatively deblocked in the allylic position. The reaction furnishes carbohydrate‐derived 2,3‐dihydro‐4H‐pyranones, which serve as starting materials for the preparation of C‐saccharides, glycosyl stannanes or thromboxane A2‐analogues. Alternatively, iodine(III) reagents can be used to oxidize halide anions. The halogen‐ate complexes thus generated behave like synthetic equivalents of acyl hypobromite and iodite, respectively, or halogen azides, which can all add to alkenes, including glycals, under very mild conditions.

Spiro[2.3]hexane‐ and Spiro[3.3]heptane‐derived α‐Amino Acids: Synthesis and Isoelectric Point Evaluation

“…HPLC purification was performed on Chromatorex 18 SMB 100-ST 100×19 mm 5 μm column, using H 2 O/MeCN gradient. 1 H and 13 C NMR spectra were recorded on a Bruker 170 Avance 500 spectrometer (at 500 MHz for 1 H NMR, 126 MHz for 13 C NMR, and 470 MHz for 19 F NMR) and Varian Unity Plus 400 spectrometer (at 400 MHz for 1 H NMR, 101 MHz for 13 C NMR and 376 MHz for 19 F NMR). NMR chemical shifts are reported in ppm (δ scale) downfield from TMS as an internal standard and are referenced using residual NMR solvent peaks at 7.26 and 77.16 ppm for 1 H and 13 C in CDCl 3, 2.50 and 39.52 ppm for 1 H and 13 C in DMSO-d 6 .…”

Essential Logic and Facts Behind the Expansion of the Genetic Code: A Critical Assessment

“…[4,5,210] These simple amino acids are among the most abundant in prebiotic chemistry and likely provided the basis for early polypeptides. [211] Over time, additional amino acids were incorporated to improve catalytic efficiency, structural stability, and chemical versatility (Figure 2C). [211] Amino acid biosynthesis and the genetic code are intimately linked, as proposed by Wong's co-evolution theory.…”

“…[211] Over time, additional amino acids were incorporated to improve catalytic efficiency, structural stability, and chemical versatility (Figure 2C). [211] Amino acid biosynthesis and the genetic code are intimately linked, as proposed by Wong's co-evolution theory. This theory postulates, "The structure of the codon system is primarily an imprint of the prebiotic pathways of amino-acid formation, which remain recognizable in the enzymatic pathways of amino-acid biosynthesis (…) The codon domains of most pairs of precursorproduct amino acids should be contiguous, i.e., separated by only the minimum separation of a single base change."…”

“…[ 211 ] Over time, additional amino acids were incorporated to improve catalytic efficiency, structural stability, and chemical versatility (Figure 2C). [ 211 ]…”

Friedel–Crafts reactions for biomolecular chemistry

“…118 Mechanistic details of tryptophan formation have not been thoroughly discussed in the report, and it is suggested that tryptophan may not have been stable enough in the prebiotic time due to a strong ultraviolet light in the early Earth. 119 The proposed formation of tryptophan amino acid (Scheme 8B, top) 116 may be relevant to an enol form of pyruvate derivatives (Scheme 8B, bottom). No literature precedents in synthetic chemistry fields exist about the reactions of nonsubstituted indole and pyruvate eventually producing tryptophan or even derivatives.…”