Biocatalytic Deacylation Studies on Tetra-O-acyl-β-d-xylofuranosyl Nucleosides: Synthesis of xylo-LNA Monomers

Regioselective Deacetylation in Nucleosides and Derivatives

Nucleoside analogues are a promising class of natural compounds in the pharmaceutical industry, and many antiviral, antibacterial and anticancer drugs have been created through structural modification of nucleosides scaffold. Acyl protecting groups, especially the acetyl group, play an important role in the protection of hydroxy groups in nucleoside synthesis and modification; consequently, numerous methodologies have been put forth for the acetylation of free nucleosides. However, for nucleosides that contain different O- and N-based functionalities, selective deprotection of the acetyl group(s) in nucleosides has been studied little, despite its practical significance in simplifying the preparation of partially or differentially substituted nucleoside intermediates. In this mini-review, recent approaches for regioselective deacetylation in acetylated nucleosides and their analogues are summarized and evaluated. Different regioselectivities (primary ester, secondary ester, full de-O-acetylation, and de-N-acetylation) are summarized and discussed in each section.

Chemo-enzymatic access to C-4′-hydroxyl-tetrahydrofurano-spironucleosides

The biocatalytic synthesis of C-4′-hydroxyl-tetrahydrofurano-spironucleosides where the tetrahydrofuranospirocyclic ring at C-4′ position locks the furanose ring of nucleosides in the NE-conformation (C4′-exo).

Enzymatic separation of epimeric 4-C-hydroxymethylated furanosugars: Synthesis of bicyclic nucleosides

Conversion of D-glucose to 4-C-hydroxymethyl-1,2-O-isopropylidene-α-D-ribofuranose, which is a key precursor for the synthesis of different types of bicyclic/spiro nucleosides, led to the formation of an inseparable 1:1 mixture of the desired product and 4-C-hydroxymethyl-1,2-O-isopropylidene-α-D-xylofuranose. A convenient environment friendly Novozyme^®-435 catalyzed selective acetylation methodology has been developed for the separation of an epimeric mixture of ribo- and xylotrihydroxyfuranosides in quantitative yields. The structure of both the monoacetylated epimers, i.e., 5-O-acetyl-4-C-hydroxymethyl-1,2-O-isopropylidene-α-D-ribo- and xylofuranose obtained by enzymatic acetylation, has been confirmed by an X-ray study on their corresponding 4-C-p-toluenesulfonyloxymethyl derivatives. Furthermore, the two separated epimers were used for the convergent synthesis of two different types of bicyclic nucleosides, which confirms their synthetic utility.

Synthesis of 3′-azido/-amino-xylobicyclonucleosides

Lipozyme® TL IM mediated the selective deacetylation of one of the two acetoxy groups in 4-C-acetoxymethyl-5-O-acetyl-3-azido-3-deoxy-1,2-O-isopropylidene-α-d-xylofuranose, leading to the first efficient syntheses of 3′-azido/3′-amino-xylobicyclonucleosides T, U, C and A.

Chemo-enzymatic synthesis of 3′-O,4′-C-methylene-linked α-l-arabinonucleosides

Biocatalytic methodology has been developed for the efficient and environment friendly synthesis of 3′-O,4′-C-methylene-linked α-l-arabinonucleosides.

Effect of acyl chain length on selective biocatalytic deacylation on O-aryl glycosides and separation of anomers

It has been demonstrated that Lipozyme® TL IM (Thermomyces lanuginosus lipase immobilised on silica) can selectively deacylate the ester function involving the C-5' hydroxyl group of α-anomers over the other acyl functions of anomeric mixture of peracylated O-aryl α,β-D-ribofuranoside. The analysis of results of biocatalytic deacylation reaction revealed that the reaction time decreases with the increase in the acyl chain length from C1 to C4. The unique selectivity of Lipozyme® TL IM has been harnessed for the separation of anomeric mixture of peracylated O-aryl α,β-D-ribofuranosides, The lipase mediated selective deacylation methodology has been used for the synthesis of O-aryl α-D-ribofuranosides and O-aryl β-D-ribofuranosides in pure forms, which can be used as chromogenic substrate for the detection of pathogenic microbial parasites containing glycosidases.

Selective biocatalytic acylation studies on 5'-O-(4,4'-dimethoxytrityl)-2',3'-secouridine: an efficient synthesis of UNA monomer

Lipozyme(®) TL IM (Theremomyces lanuginosus lipase immobilized on silica) in toluene catalyzes the acylation of the 2'-OH over the 3'-OH group in 5'-O-(4,4'-dimethoxytrityl)-2',3'-secouridine (5'-O-DMT-2',3'-secouridine) in a highly selective fashion in moderate to almost quantitative yields. The turn over during benzoyl transfer reactions mediated by vinyl benzoate or benzoic anhydride was faster than in acyl transfer reactions with vinyl acetate or C(1) to C(5) acid anhydrides; except in the case of butanoic anhydride. The 2'-O-benzoyl-5'-O-DMT-2',3'-secouridine obtained by Lipozyme(®) TL IM catalyzed benzoylation of 5'-O-DMT-2',3'-secouridine was successfully converted into its 3'-O-phosphoramidite derivative in satisfactory yield, which is a building block for the preparation of oligonucleotides containing the uracil monomer of UNA (unlocked nucleic acid).