27372-03-8

Six new partially acylated resin glycosides were isolated from convolvulin of Ipomoea purga, Ipomoea stans, and Ipomoea murucoides (Convolvulaceae). The structures of compounds 1–6 were elucidated by a combination of NMR spectroscopy and mass spectrometry. The structure of jalapinoside B (1) consists of a hexasaccharide core bonded to an 11-hydroxytetradecanoic (convolvulinic) acid forming a macrolactone acylated by a 2-methylbutanoyl, a 3-hydroxy-2-methylbutanoyl, and a quamoclinic acid B units. Purginoic acid A (2) contains a hexasaccharide core bonded to a convolvulinic acid acylated by a 3-hydroxy-2-methylbutanoyl unit. Stansin A (4) is an ester-type heterodimer, and consists of two stansoic acid A (3) units, acylated by 2-methylbutanoic and 3-hydroxy-2-methylbutanoic acids. The site of lactonization was located at C-3 of Rhamnose, and the position for the ester linkage of the monomeric unit B on the macrolactone unit A was established as C-4 of the terminal rhamnose. Compounds 5 and 6 are glycosidic acids. Murucinic acid II (5) is composed of a pentasaccharide core bonded to an 11-hydroxyhexadecanoic (jalapinolic) acid, acylated by an acetyl unit. Stansinic acid I (6) is a tetrasaccharide core bonded to a jalapinolic acid, acylated by 2-methylbutanoyl and 3-hydroxy-2-methylbutanoyl units. Preliminary testing showed the cytotoxicity of compounds 1–6 toward OVCAR and UISO-SQC-1 cancer cell lines. In addition, compound 1 showed an antiproliferative activity on glioma C6 and RG2 tumor cell lines. Copyright

A screening of 15 fungi and yeast strains was carried out in fermentation processes to perform the diastereo- and enantioselective reduction of ethyl 2-methyl-3-oxobutanoate, to the corresponding (R*,S*)-3-hydroxy-2-methyl esters. Overall, biotransformations led to excellent conversions, as well as good to excellent diastereo- and enantioselectivities. A strain of Aureobasidium pullulans (CCM H1) was found to be the most efficient biocatalyst in terms of conversion (100%), syn:anti ratio (3:97), and enantiomeric excess (94% anti-(2S,3S) isomer). This biotransformation was successfully carried out on a preparative level as well. Other microorganisms, such as Fusarium graminearum (CCM HH 224), Aspergillus terreus (BFQU 121), Geotrichum candidum (CCM H38), Trichoderma koningii (ATCC 76666), and Aspergillus niger (CCM H21) also showed excellent diastereo- and enantioselectivities, combined with high conversions (>95% conversion, ≥95% ee, and excellent syn:anti ratios). Many of the strains used in this work had scarcely been described as oxido-reducing agents, or had never been used with the substrates reported herein.

Novel methods for the reduction of α,β-epoxy ketones, α,β-epoxy esters (glycidic esters), and their congeners to β-hydroxy carbonyl compounds (aldols) by the use of organoselenium reagents are described. The reagents, a sodium phenylseleno(triethyl)borate complex Na[PhSeB(OEt)3] easily prepared by reduction of (PhSe)2 with NaBH4 in EtOH and benzeneselenol (PhSeH) generated in situ from the borate complex by addition of acetic acid, have been demonstrated to serve as excellent reducing agents for these transformations. The organoselenium-mediated reduction of α,β-epoxy carbonyl compounds regiospecifically occurs at the α-carbon to produce a wide variety of cyclic (intramolecular) aldols as well as acyclic (intermolecular) ones in excellent yields. Quantitative mechanistic studies have revealed that the organoselenium-mediated reduction proceeds via an α-substitution process in contrast to the common electron transfer reducing agents.

α,β-Epoxy esters were reduced to β-hydroxy esters with an organoselenium reagent, Na+-, via α-substitution process.