A One Step Conversion of Glycals To 2‑Azido-2-Deoxysugars and Sugar Derived Enones Using Hypervalent Iodine Chemistry

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Mini symposium: Glycobiology at the LUMC and beyond

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A One Step Conversion of Glycals To 2‑Azido-2-Deoxysugars and Sugar Derived Enones Using Hypervalent Iodine Chemistry

Ande Chennaiah 1 , Y. D. Vankar 2 , Eoghan McGarrigle 1

1 University College Dublin, Dublin, Ireland, 2Indian Institute of Technology Kanpur, Kanpur, India

2-Acetamido-2-deoxysugars are extremely useful intermediates which form a part of several oligosaccharides and glycoconjugates (glycolipids, glycopeptides and glycoproteins), biomolecules that play crucial roles in many biological processes.¹ Among others, 2-azido-2-deoxysugars serve as excellent precursors for 2-acetamido-2-deoxysugars. Owing to the difficulties associated in their preparation with regio- as well as stereoselectivity, very few methodologies are available for the synthesis of 2‑Azido-2-deoxysugars.²

Now, we present a new metal-free protocol for one-step highly regiospecific, and stereoselective conversion of glycals into 2-azido-2-deoxysugars by using a new reagent system comprised of PIFA-Me₃SiN₃-H₂O, catalyzed by TEMPO, and in presence of n-Bu₄NHSO₄ as a phase-transfer catalyst.³ The reaction conditions are mild (0 °C), the yields of the products are generally high, requiring only short reaction time (20-60 min.), and the substrate scope is also large with differently protected glycals. The present methodology does not require stringent conditions to exclude moisture. These reactions can be done on gram scale in high yield. Application of this methodology in a short synthesis of an important trisaccharide unit bound by monoclonal anti-I Ma antibody will also be discussed.

Additionally, we also reveal a novel and efficient one-step protocol for the direct oxidation of 3-O-benzyl or 3-O-silyl-protected glycals to the corresponding enones with PIFA-TEMPO and water as a reagent system.⁴ The reaction generally proceeds in high yields under mild conditions in short time. In addition, this oxidation protocol was found to be independent of the stereochemistry of the -Bn and -OTBDMS groups at C3 of glycals. Moreover, since the reactions are performed in presence of water, exclusion of moisture is not necessary.

Synthesis of 2-Azido-2-deoxy sugars and sugar derived enones

a) Bongat, A. F. G.; Demchenko, A. V. Carbohydr. Res. 2007, 342, 374−406. b) Mirabella, S.; Cardona, F.; Goti, A. Org. Biomol. Chem. 2016, 14, 5186−5204.

a) Lemieux, R. U.; Ratcliffe, R. M. Can. J. Chem. 1979, 57, 1244−1251. b) Seeberger, P. H.; Roehrig, S.; Schell, P.; Wang, Y.; Christ, W. J. Carbohydr. Res. 2000, 328, 61−69.

Chennaiah, A.; Vankar, Y. D. Org. Lett. 2018, 20, 2611−2614.

Chennaiah, A.; Verma, A. K.; Vankar, Y. D. J. Org. Chem. 2018, 83, 10535−10540.

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