Petri Tähtinen

Candida antarctica lipase A in the dynamic resolution of novel furylbenzotiazol-based cyanohydrin acetates

A series of novel (R)-furylbenzotiazol-based cyanohydrin acetates were prepared in over 90% isolated yields from the corresponding furancarbaldehydes. The one-pot method combines a basic resin to produce hydrogen cyanide from acetone cyanohydrin, an equilibrium between the formation and decomposition of furylbenzotiazol-based cyanohydrins and the unique enantioselectivity of Candida antarctica lipase A, allowing the acylation of (R)-cyanohydrins in the presence of vinyl acetate in anhydrous acetonitrile.

Preparation of novel phenylfuran-based cyanohydrin esters: lipase-catalysed kinetic and dynamic resolution

A series of novel (R)-5-phenylfuran-2-yl cyanomethyl butanoates were prepared by Pseudomonas cepacia lipase- catalysed dynamic kinetic resolution in toluene. The method exploits a basic resin both for the racemization and formation of phenylfuran-based cyanohydrins and for the decomposition of acetone cyanohydrin in one-pot with enzymatic enantioselective acylation using vinyl butanoate. The lipase-catalysed methanolysis of racemic 5-phenylfuran-2-yl cyanomethyl butanoates in toluene with E 100 was shown to be usable when the corresponding (S)-butanoates are needed. Candida antarctica lipase A provided racemic cyanohydrin butanoates with quantitative chemical yields under mild conditions.

Biological activity of ellagitannins: Effects as anti-oxidants, pro-oxidants and metal chelators

Ellagitannins are a subclass of hydrolysable tannins that have been suggested to function as defensive compounds of plants against herbivores. However, it is known that the conditions in the digestive tracts of different herbivores are variable, so it seems reasonable to anticipate that the reactivities and modes of actions of these ingested defensive compounds would also be different. A previous study on a few ellagitannins has shown that these polyphenolic compounds are highly oxidizable at high pH and that their bioactivity can be attributed to certain structural features. Herein, the activities of 13 ellagitannins using the deoxyribose assay were measured. The results provided information about the anti-oxidant, pro-oxidant and metal chelating properties of ellagitannins. Surprisingly, many of the tested ellagitannins exhibited pro-oxidant activities even at neutral pH and only moderate to low radical scavenging activities, although the metal chelating capacities of all tested ellagitannins were relatively high.

Structure-Based Engineering of Angucyclinone 6-Ketoreductases

Angucyclines are tetracyclic polyketides produced by Streptomyces bacteria that exhibit notable biological activities. The great diversity of angucyclinones is generated in tailoring reactions, which modify the common benz[a]anthraquinone carbon skeleton. In particular, the opposite stereochemistry of landomycins and urdamycins/gaudimycins at C-6 is generated by the short-chain alcohol dehydrogenases/reductases LanV and UrdMred/CabV, respectively. Here we present crystal structures of LanV and UrdMred in complex with NADP(+) and the product analog rabelomycin, which enabled us to identify four regions associated with the functional differentiation. The structural analysis was confirmed in chimeragenesis experiments focusing on these regions adjacent to the active site cavity, which led to reversal of the activities of LanV and CabV. The results surprisingly indicated that the conformation of the substrate and the stereochemical outcome of 6-ketoreduction appear to be intimately linked.

Epimers vs. inverse epimers: the C-1 configuration in alnumycin A1

The determination of whether two stereoisomers constitute an epimeric pair or if they differ in their configuration at all stereogenic centers bar one can be deceptive, and even more problematic than just absolute configuration determination per se. The latter stereochemical relationship is hereby defined as a pair of inverse epimers and is exemplified by alnumycin A1 to introduce the concept.

Phenolic Compounds and Their Fates In Tropical Lepidopteran Larvae: Modifications In Alkaline Conditions

Lepidopteran larvae encounter a variety of phenolic compounds while consuming their host plants. Some phenolics may oxidize under alkaline conditions prevailing in the larval guts, and the oxidation products may cause oxidative stress to the larvae. In this study, we aimed to find new ways to predict how phenolic compounds may be modified in the guts of herbivorous larvae. To do so, we studied the ease of oxidation of phenolic compounds from 12 tropical tree species. The leaf extracts were incubated in vitro in alkaline conditions, and the loss of total phenolics during incubation was used to estimate the oxidizability of extracts. The phenolic profiles of the leaf extracts before and after incubation were compared, revealing that some phenolic compounds were depleted during incubation. The leaves of the 12 tree species were each fed to 12 species of lepidopteran larvae that naturally feed on these trees. The phenolic profiles of larval frass were compared to those of in vitro incubated leaf extracts. These comparisons showed that the phenolic profiles of alkali-treated samples and frass samples were similar in many cases. This suggested that certain phenolics, such as ellagitannins, proanthocyanidins, and galloylquinic acid derivatives were modified by the alkaline pH of the larval gut. In other cases, the chromatographic profiles of frass and in vitro incubated leaf extracts were not similar, and new modifications of phenolics were detected in the frass. We conclude that the actual fates of phenolics in vivo are often more complicated than can be predicted by a simple in vitro method.

Hybrid compounds generated by the introduction of a nogalamycin-producing plasmid into Streptomyces argillaceus

The combination of genetic material from different antibiotic-producing organisms is a versatile and ever-expanding approach for the production of novel, hybrid compounds possessing bioactivity. The introduction of a plasmid (pSY21b) derived from Streptomyces nogalater and encoding PKS for nogalamycin production into the host strain S. argillaceus A43 led to the production of three new compounds in addition to the normally produced mithramycin. The new compounds are hybrids in the sense that they share features associated with the genes of both the host and the introduced plasmid. The structural elucidation of the novel compounds relied primarily on NMR spectroscopy, which revealed the three hybrids to be glycosides with the same aglycone common to all. Determination of the relative stereochemistry within the aglycone unit was confirmed by single-crystal X-ray analysis of the aglycone, which also revealed the tautomeric equilibrium to be in a very different position in comparison to that in the solution state. The glycosylation profile was clearly determined by the host, as the typical mithramycin sugars, D-oliose, D-olivose, and D-mycarose, were all expressed. Notable for the mutant was the high titre of the shunt products, 60% of the metabolic output, together with a lack of structural diversity of the hybrid aglycone present in the products, two features which are not normally observed.

Structures of pyrrolo-1,3-heterocycles prepared from 3-aroylpropionic acid and cyclic aminoalcohols: An NMR and X-ray diffraction study

By the reaction of 3-(4-chlorobenzoyl)propionic acid 1 with 1,2- and 1,3-bifunctional compounds, new condensed heterocycles have been prepared. Thus, the reaction of 1 with hydrazine gave the pyridazin-3-one 2 and with ethylenediamine, the pyrrolo[1,2-a]imidazole 3 was formed. Reaction of compound 1 and 2-aminoethanol yielded the pyrrolo[2,1-b]oxazolidinone 4 and the reaction with 3-aminopropan-1-ol resulted in the pyrrolo[2,1-b][1,3]oxazinone 5. With o-aminothiophenol tricyclic pyrrolo[2,1-b]benzothiazolone 6 was prepared. In comparison with 4–6, the structure of the new tri- and tetra-cyclic compounds 7–14 are discussed. With the starting oxoacid 1, the cyclic and bicyclic aminoalcohols gave the following fused heterocycles: cis- and trans-2-(hydroxymethyl)cyclohexane- and cyclohex-4-ene-amines yielded pyrrolo[1,2-a][3,1]benzoxazinones 7–10, diexo-3-(hydroxymethyl)bicyclo[2.2.1]heptane-2-amine and hept-5-ene-2-amine yielded the diexo (11 and 12) and diendo (13 and 14) methylene-bridged pyrrolo[1,2-a][3,1]benzoxazinones. The structures of the compounds were proved by 1D 1H and 13C NMR spectroscopy, NOE difference spectroscopy and several different homo- and hetero-nuclear multipulse techniques (COSY, NOESY, HETCOR). The 1D 1H NMR spectra were analysed by iterative spin-simulation using PERCH-software. Many interesting long-range couplings were found. Some aid for structural elucidation was gained from molecular modelling calculations. The crystal structures of 7, 9–11, 13 and 14 elucidated from the X-ray diffraction measurements do not differ significantly from the solution structures.

Isolation of chemically well-defined semipreparative liquid chromatography fractions from complex mixtures of proanthocyanidin oligomers and polymers

In this study, a semipreparative liquid chromatography method was developed for the isolation of chemically well-defined proanthocyanidin (PA) oligomer and polymer fractions. The aim was to achieve better separation than traditionally achieved for the PAs with other chromatographic methods. The method was tested with eleven PA rich Sephadex LH-20 fractions, which originated from eleven different plant species. The resulting semipreparative fractions were analyzed by both triple quadrupole and high-resolution mass spectrometry assisted by ultrahigh-performance liquid chromatography (UPLC) separation. The results showed remarkable differences in the procyanidin to prodelphinidin ratio, mean degree of polymerization, and specific oligomeric and polymeric content. However, some of these features indicated consistent patterns between species as the function of UPLC retention time. The developed method enables the production of tens of well-defined fractions of PA oligomers and polymers from the unresolved chromatographic PA hump. Accordingly, this allows researchers to explore the most bioactive parts of the complex PA humps of any plant species, which have not been possible earlier.

The assignment of the correct structures and conformational analysis of the isomeric t-5- and t-4-phenyl-t(c)-2-benzoyl-r-1-cyclohexanecarboxylic acids by NMR and FT-IR spectroscopy

The AlCl3 catalysed addition of benzene to cis-2-benzoylcyclohex-4-enecarboxylic acid results in the product, t-5-phenyl-c-2-benzoyl-r-1-cyclohexanecarboxylic acid (2), but not in its 2-trans epimer (5) as has been reported previously in the literature. The latter was obtained instead by treating 2 with NaOH in EtOH–H2O. The structures and conformational assignment of 2, its 4-trans phenyl positional isomer (4), and both their 2-trans benzoyl epimers (5 and 6, respectively, prepared by base-induced epimerisation) were elucidated by means of NMR spectroscopy. The postulated trans→cis transformation of the 2-trans isomer 5 to the product 2 does not in fact occur; indeed it is the reverse transformation that is viable. All of the compounds showed substantial intramolecular hydrogen-bonding in solution (e.g. in CDCl3) by FT-IR measurements and, furthermore, a dynamic equilibrium between hydrogen-bonded and non hydrogen-bonded forms was observed by NMR for compound 2.