Progress and challenges in the synthesis of sequence controlled polysaccharides

• Giulio Fittolani,
• Theodore Tyrikos-Ergas,
• Denisa Vargová,
• Manishkumar A. Chaube and
• Martina Delbianco

Beilstein J. Org. Chem. 2021, 17, 1981–2025, doi:10.3762/bjoc.17.129

Double-headed nucleosides: Synthesis and applications

• Vineet Verma,
• Jyotirmoy Maity,
• Vipin K. Maikhuri,
• Ritika Sharma,
• Himal K. Ganguly and
• Ashok K. Prasad

Beilstein J. Org. Chem. 2021, 17, 1392–1439, doi:10.3762/bjoc.17.98

• . The convergent synthesis of the double-headed nucleosides was achieved from uridine, which was first converted to the 3′,5′-(1,1,3,3-tetraisopropyldisiloxan-1,3-diyl)-protected (TIPDS) ketonucleoside 1 following a standard procedure [40]. The subsequent Corey–Chaykovsky epoxidation [41] of 2

• ′-ketonucloside 1 with trimethylsulfoxonium iodide in DMSO afforded the spironucleoside 2, which in turn was converted to the TIPDS-protected 2′-(pyrimidin-1-yl)methyl-/2′-(purin-9-yl)methylarabinofuranosyluracil derivatives 3a–f by nucleophilic epoxide ring opening with thymine, N-benzoyladenine, 6-O-allyl-N

• ]. Nielsen and co-workers [42] additionally synthesized 2′-(N-benzoylcytosin-1-yl)methylarabinofuranosyl-N-benzoylcytosine (7) from uridine using a similar methodology. Thus, the nucleophilic epoxide ring opening in spironucleoside 2 with uracil in DMF in a N1-regioselective manner afforded the TIPDS

Beyond ribose and phosphate: Selected nucleic acid modifications for structure–function investigations and therapeutic applications

• Christopher Liczner,
• Kieran Duke,
• Gabrielle Juneau,
• Martin Egli and
• Christopher J. Wilds

Beilstein J. Org. Chem. 2021, 17, 908–931, doi:10.3762/bjoc.17.76

• ) (TIPDS) protected uridine, protection of N3 was needed in order to prevent methylation at this position (Scheme 4). The N3-benzoylated derivative could then be treated with methyl iodide in the presence of silver oxide in order to methylate the 2'-OH. A similar strategy was employed to synthesize 3',5'-O

• -TIPDS-N4-benzoyl-2'-O-methylcytidine. Next, 3',5'-O-TIPDS-N6-benzoyladenosine suffered from methylation at the nucleobase and thus, 6-chloro-9-β-ᴅ-ribofuranosylpurine was instead used as the starting material. Once TIPDS protected, the 2'-OH could, once again, be selectively methylated with methyl

• iodide and silver oxide. The protected adenine base was regenerated by treatment with ammonia followed by benzoylation. Once the methyl group was incorporated into these ribonucleosides, the TIPDS group was selectively removed by tetrabutylammonium fluoride (TBAF) or hydrochloric acid treatment, followed

Towards the total synthesis of chondrochloren A: synthesis of the (Z)-enamide fragment

• Jan Geldsetzer and
• Markus Kalesse

Beilstein J. Org. Chem. 2020, 16, 670–673, doi:10.3762/bjoc.16.64

• )-bromide 4 we decided to use a (Z)-selective Buchwald-type reaction encouraged by the previous works of the Buchwald group on producing (E)-enamide coupling products [13][14][15]. The synthesis of the amide 3 started with TIPDS-protection of commercially available ᴅ-ribonic acid-1,4-lactone (5) (Scheme 1

• ). A subsequent transesterification under mild conditions with Bu2SnO provided dihydroxy ester 7 in 72% yield. The 1,3-diol in 7 was methylated with an excess of the Meerwein reagent and TIPDS-removal afforded ester 9 in good yields. A double TBS-protection and liberation of the primary alcohol

Aminosugar-based immunomodulator lipid A: synthetic approaches

• Alla Zamyatina

Beilstein J. Org. Chem. 2018, 14, 25–53, doi:10.3762/bjoc.14.3

Silyl-protective groups influencing the reactivity and selectivity in glycosylations

• Mikael Bols and
• Christian Marcus Pedersen

Beilstein J. Org. Chem. 2017, 13, 93–105, doi:10.3762/bjoc.13.12

• available silyl-protective groups are trimethylsilyl (TMS), triethylsilyl (TES), tert-butyldimethylsilyl (TBS), tert-butyldiphenylsilyl (TBDPS), triisopropylsilyl (TIPS) as well as the diol-protective groups DTBS and TIPDS (Figure 1). Silyl groups have also early been used in the carbohydrate field to

• excess donor in diethyl ether since this gave the best α-selectivity (Scheme 2). Using other protective groups on the fucose part, such as 2,3-TIPDS and 4-O-TES led to glycosylation with only poor stereoselectivity [8]. The TES groups were also used successfully on the 2-methylamino analogue of 4. A

• with this, the analogue of 46 having a TIPDS group rather than a DTBS was not particularly unreactive, as it is more flexible due to the bigger ring. The Yang group used 46 in a one-pot synthesis of a trisaccharide, where they took advantage of 46 being less reactive than partially benzoylated

Brønsted acid-promoted azide–olefin [3 + 2] cycloadditions for the preparation of contiguous aminopolyols: The importance of disiloxane ring size to a diastereoselective, bidirectional approach to zwittermicin A

• Hubert Muchalski,
• Ki Bum Hong and
• Jeffrey N. Johnston

Beilstein J. Org. Chem. 2010, 6, 1206–1210, doi:10.3762/bjoc.6.138

• benzyl azide with α,β-unsaturated imides. Using a strong Brønsted acid (triflic acid) to activate the electron deficient imide π-bond, high diastereoselection was observed provided that a 1,1,3,3-tetraisopropoxydisiloxanylidene group (TIPDS) is used to restrict the conformation of the central 1,3-anti

• diol. This development provides a basis for a stereocontrolled approach to the aminopolyol core of (−)-zwittermicin A using a bidirectional synthesis strategy. Keywords: azide; bidirectional synthesis; cycloaddition; dialkoxydisiloxane; TIPDS; triazoline; triflic acid; zwittermicin A; Introduction

• , diastereoselective sequence of two [3 + 2] cycloaddition reactions promoted by triflic acid where the large 1,3-diol protecting group – the 1,1,3,3-tetraisopropoxydisiloxanylidene group (TIPDS) – plays a crucial role in facial discrimination. Results and Discussion Our approach to the preparation of enantiomerically