Vesna Petrović

Synthesis, intramolecular migrations and enzymic hydrolysis of partially pivaloylated methyl α-d-mannopyranosides

A series of methyl O-pivaloyl-alpha-D-mannopyranosides was synthesized using pivaloyl chloride in pyridine. The 3,6-di-O-pivaloyl derivative 6 undergoes intramolecular transesterification in neutral conditions (buffer, pH 7.2) to give its 2,6-di-O-pivaloyl analogue 5. The course of this migration was followed using 14C-labelled 6. As opposed to 6 compound 5 was shown to be a good substrate for esterases present in rabbit serum. Thus, regioselective enzymic hydrolysis led to the preferential cleavage of the 2-OPiv group to yield a mixture of 2- and 6-O-monopivalates in a ratio of 1:2.6.

Synthesis and intramolecular transesterifications of pivaloylated methyl α-d-galactopyranosides

Abstract Selective pivaloylations of methyl α- d -galactopyranoside have been studied under various reaction conditions. Partially pivaloylated products were submitted to additional acetylations. The structures were established by 1 H and 13 C NMR spectroscopies. Both, 2,6- and 3,6-dipivalates underwent intramolecular cyclization in neutral conditions (phosphate buffered saline, pH 7.2) to give a stable 2,3-orthoacid with a parallel 6→4 migration of the pivaloyl group.

Synthesis of acylated methyl -β-d-xylopyranosides and their enzymic deacylations by rabbit serum esterases

Selective pivaloylations of methyl beta-D-xylopyranoside have been studied under various reaction conditions. Partially pivaloylated products were submitted to additional acetylations. The structures were established by 1H NMR spectroscopy. Representatives of acylated methyl beta-D-xylopyranosides (acyl being pivaloyl, acetyl, or a combination of both) were submitted to hydrolysis catalyzed by rabbit serum and esterases isolated from rabbit serum.

Synthesis and Enzymic Hydrolysis of Acylated Adenosine Derivatives

Abstract Various derivatives of adenosine were prepared by acylation of adenosine (6‐amino‐9‐(β‐D‐ribofuranosyl)purine (1) with different molar equivalents of acetic anhydride and/or pivaloyl chloride in pyridine. Compounds 6‐acetylamino‐9‐[(2,3,5‐tri‐O‐acetyl)‐β‐D‐ribofuranosyl]purine (3), 6‐amino‐9‐[(2,3,5‐tri‐O‐acetyl)‐β‐D‐ribofuranosyl]purine (4), and 6‐pivaloylamino‐9‐[(2,3,5‐tri‐O‐pivaloyl)‐β‐D‐ribofuranosyl]purine (5) were subsequently submitted to hydrolysis catalyzed by a number of hydrolytic enzymes. Regioselective enzymic deacetylation at the primary hydroxyl group of 3 and 4 with butyrylcholinesterase (BChE) produced 6‐acetylamino‐9‐[(2,3‐di‐O‐acetyl)‐β‐D‐ribofuranosyl]purine (9) and 6‐amino‐9‐[(2,3‐di‐O‐acetyl‐β‐D‐ribofuranosyl]purine (10), respectively. All structures were established by 1H and 13C NMR spectroscopies.

Synthesis of Acylated Methyl 2‐Acetamido‐2‐Deoxy‐α‐D‐Mannopyranosides

Abstract 2‐Acetamido‐2‐deoxy‐β‐D‐mannopyranose (1) was glycosylated by the Fischer method using an acidic ion‐exchange resin as the catalyst to give α‐methyl glycoside 2. Selective pivaloylations of methyl 2‐acetamido‐2‐deoxy‐α‐D‐mannopyranoside (2) have been studied under various reaction conditions. Two partially pivaloylated products were submitted to additional acetylations. All structures were established by NMR spectroscopy. Structure of the methyl 2‐acetamido‐2‐deoxy‐3,6‐di‐O‐pivaloyl‐α‐D‐mannopyranoside (4) was determined by X‐ray analysis.

Methyl 3,4-di-O-pivaloyl-β-d-xylo­pyran­oside

The crystal and molecular structure of the title compound, C16H28O7, has been determined by X-ray analysis at 100 K. The six-membered ring adopts the chair conformation. Molecules are connected in pairs around twofold rotation axes via two O—H⋯O hydrogen bonds with 2.852 (2) A.

Methyl 4‐O‐pivaloyl‐β‐d‐xylopyran­oside

The six-membered ring of the title compound, C_11 H_20 O_6, adopts the chair conformation, with the 4-O-pivaloyl group in an equatorial position. Two vicinal hydroxyl groups of each molecule form four hydrogen bonds of the O-H...O type in a one-dimensional chain running along the b axis.