1. Synthesis of chiral 1,4-oxazepane-5-carboxylic acids from polymer-supported homoserine
Petra Králová, Barbora Lemrová, Michal Maloň, Miroslav Soural RSC Adv. 2020 Sep 30;10(59):35906-35916. doi: 10.1039/d0ra07997a. eCollection 2020 Sep 28.
The preparation of novel 1,4-oxazepane-5-carboxylic acids bearing two stereocenters is reported in this article. Fmoc-HSe(TBDMS)-OH immobilized on Wang resin was reacted with different nitrobenzenesulfonyl chlorides and alkylated with 2-bromoacetophenones to yield N-phenacyl nitrobenzenesulfonamides. Their cleavage from the polymer support using trifluoroacetic acid (TFA) led to the removal of the silyl protective group followed by spontaneous lactonization. In contrast, TFA/triethylsilane (Et3SiH)-mediated cleavage yielded 1,4-oxazepane derivatives as a mixture of inseparable diastereomers. The regioselectivity/stereoselectivity depended on the substitution of the starting 2-bromoacetophenones and was studied in detail. Catalytic hydrogenation of the nitro group improved the separability of the resulting diastereomeric anilines, which allowed us to isolate and fully characterize the major isomers.
2. Oligoribonucleotides with 2'-O-(tert-butyldimethylsilyl) groups
L Bellon Curr Protoc Nucleic Acid Chem. 2001 May;Chapter 3:Unit 3.6. doi: 10.1002/0471142700.nc0306s01.
The chemical synthesis of oligoribonucleotides on solid support is routinely performed via the phosphoramidite method. However, the additional 2-OH function of the ribofuranosyl sugar requires suitable protection during oligoribonucleotide synthesis. This unit describes methods for 2-OH protection using the TBDMS group.
3. Synthesis of 2'-O-substituted ribonucleosides
V Serebryany, L Beigelman Nucleosides Nucleotides Nucleic Acids. 2003 May-Aug;22(5-8):1007-9. doi: 10.1081/NCN-120022724.
An efficient synthesis of 2'-O-substituted ribonucleosides, including 2'-O-TBDMS and 2'-O-TOM protected as well as 2'-O-Me and 2'-O-allyl derivatives is presented. Di-t-butylsilylene group was employed for simultaneous protection of 3'- and 5'- hydroxyl functions of nucleoside on the first step. Subsequent silylation or alkylation of free 2'-OH followed by introduction of suitable protection on the base moiety and removal of cyclic silyl protection gave target compounds in a high yield.
