(S)‐6‐Bromo‐BINOL‐based phosphoramidite ligand with C1 symmetry for enantioselective hydrogenation and allylic substitution

(S)‐6‐Br‐BINOL‐derived phosphoramidite, a s imple monodentate ligand with a stereogenic center at the phosphorus atom, was synthesized for the first time. This stereoselector generated a high level of enantioselectivity (80–95% ee) in the rhodium‐catalyzed hydrogenation of α‐dehydrocarboxylic acid esters and was also successfully employed in the asymmetric palladium‐catalyzed allylic substitution of (E)‐1,3‐diphenylallyl acetate. The optical yield also showed significant dependence with reaction type: up to 70% ee for allylic amination, up to 75% ee for allylic sulfonylation, and up to 90% ee for allylic alkylation. Chirality, 2010. © 2010 Wiley‐Liss, Inc.     

Steric Considerations on Improving the Diastereomeric Ratio of (+)‐ and (−)‐Neomenthyl Phenyl Sulfoxides Using Bulky‐Headed Oxidant Hexadecyltrimethylammonium Periodate and Assignment of Their Configuration

The bulky‐headed oxidant hexadecyltrimethylammonium periodate affords the diastereomeric pairs, (Ss)‐(+)/(Rs)‐(+) and (Ss)‐(?)/(Rs)‐(?)‐neomenthyl phenyl sulfoxides in stereochemically pure states with improved diastereomeric excess (48% diastereomeric excess [de]) as compared to its nonbulky counterpart, sodium metaperiodate (28% de) from respective (+)/(?)‐neomenthyl phenyl sulfides. Steric effects involving the head group volume of hexadecyltrimethylammonium periodate is found to play a role in improving the diastereomeric ratio of the products. The two diastereomers can be readily separated by column chromatography. Absolute configuration at the sulfur center in (+)‐neomenthyl phenyl sulfoxide was determined by single‐crystal X‐ray crystallography and found to be Ss. Relative configurations of other sulfoxides were assigned based on the configuration of (+)‐neomenthyl phenyl sulfoxide. Chirality 27:370–374, 2015. © 2015 Wiley Periodicals, Inc.     

A peptide methionine sulfoxide reductase highly expressed in photosynthetic tissue in Arabidopsis thaliana can protect the chaperone-like activity of a chloroplast-localized small heat shock protein

The oxidation of methionine residues in proteins to methionine sulfoxides occurs frequently and protein repair by reduction of the methionine sulfoxides is mediated by an enzyme, peptide methionine sulfoxide reductase (PMSR, EC 1.8.4.6), universally present in the genomes of all so far sequenced organisms. Recently, five PMSR‐like genes were identified in Arabidopsis thaliana, including one plastidic isoform, chloroplast localised plastidial peptide methionine sulfoxide reductase (pPMSR) that was chloroplast‐localized and highly expressed in actively photosynthesizing tissue ( Sadanandom A et al., 2000 ). However, no endogenous substrate to the pPMSR was identified. Here we report that a set of highly conserved methionine residues in Hsp21, a chloroplast‐localized small heat shock protein, can become sulfoxidized and thereafter reduced back to methionines by this pPMSR. The pPMSR activity was evaluated using recombinantly expressed pPMSR and Hsp21 from Arabidopsis thaliana and a direct detection of methionine sulfoxides in Hsp21 by mass spectrometry. The pPMSR‐catalyzed reduction of Hsp21 methionine sulfoxides occurred on a minute time‐scale, was ultimately DTT‐dependent and led to recovery of Hsp21 conformation and chaperone‐like activity, both of which are lost upon methionine sulfoxidation ( Härndahl et al., 2001 ). These data indicate that one important function of pPMSR may be to prevent inactivation of Hsp21 by methionine sulfoxidation, since small heat shock proteins are crucial for cellular resistance to oxidative stress.     

HPLC with carbohydrate carbamate chiral phases: Influence of chiral phase structure on enantioselectivity

The enantioselective resolution of trans-stilbene oxide and of 23 chiral sulfoxides was investigated on cellulose and amylose tris(arylcarbamate) stationary phases coated on aminopropylated 7 μm spherical silica with 500 Å diameter pores. Cellulose tris-(3,5 dimethylphenylcarbamate) showed good resolving power for many of the sulfoxides and amylose tris-(3,5 dimethoxyphenylcarbamate) showed advantages for the resolution of certain sulfoxides which were not separated on other phases. © 1994 Wiley-Liss, Inc.     

Crystal structures of ligand‐bound octaprenyl pyrophosphate synthase from Escherichia coli reveal the catalytic and chain‐length determining mechanisms

Octaprenyl pyrophosphate synthase (OPPs) catalyzes consecutive condensation reactions of one allylic substrate farnesyl pyrophosphate (FPP) and five homoallylic substrate isopentenyl pyrophosphate (IPP) molecules to form a C₄₀ long‐chain product OPP, which serves as a side chain of ubiquinone and menaquinone. OPPs belongs to the trans‐prenyltransferase class of proteins. The structures of OPPs from Escherichia coli were solved in the apo‐form as well as in complexes with IPP and a FPP thio‐analog, FsPP, at resolutions of 2.2–2.6 Å, and revealed the detailed interactions between the ligands and enzyme. At the bottom of the active‐site tunnel, M123 and M135 act in concert to form a wall which determines the final chain length. These results represent the first ligand‐bound crystal structures of a long‐chain trans‐prenyltransferase and provide new information on the mechanisms of catalysis and product chain elongation. Proteins 2015; 83:37–45. © 2014 Wiley Periodicals, Inc.     

Synthesis and application of the first planar chiral strong Brønsted acid organocatalysts

The synthesis of planar chiral strong Brønsted acid organocatalysts derived from [2.2]paracyclophane is described. Resolution was accomplished according to a modified protocol involving pseudo‐ortho‐substituted [2.2]paracyclophane‐based sulfoxides for the synthesis of three new sulfonic acids. The first planar chiral phosphoric acid diester was obtained from the corresponding phenyl‐substituted diol derived from enantiopure 4‐bromo‐12‐hydroxy [2.2]paracyclophane. These new classes of catalysts were tested in an enantioselective Friedel–Crafts reaction as well as in a direct asymmetric Mannich reaction and gave yields of up to 93% and ee‐values of up to 38%. Chirality, 2012. © 2012 Wiley Periodicals, Inc.     

Facile Diastereoseparation of Glycosyl Sulfoxides by Chiral Stationary Phase

Separation of the diastereomers of glycosyl sulfoxides differing in the sulfur chirality has been difficult. This article presents a fast and scalable method for their diastereoseparation using a chiral stationary phase. The usefulness of this method was demonstrated in a 500‐mg scale separation within 20 min, and in the separation of trisaccharyl sulfoxide diastereomers. Chirality 28:534–539, 2016. © 2016 Wiley Periodicals, Inc.     

Electroenzymatic Synthesis of Chiral Sulfoxides

Chloroperoxidase (CPO) from Caldariomyces fumago (E.C. 1.11.1.10) is able to enantioselectively oxidize various sulfides to the corresponding (R)‐enantiomer of the sulfoxides. For these oxidations the enzyme requires an oxidant. Most commonly, tert‐butyl hydroperoxide (TBHP) and hydrogen peroxide are used. As it is known that these oxidants inactivate the enzyme, the enzymatic reaction was combined with the electrochemical in situ generation of hydrogen peroxide. As substrates for this combination of an enzymatic and an electrochemical reaction methyl p‐tolyl sulfide, 1‐methoxy‐4‐(methylthio)benzene and N‐MOC‐L ‐methionine methyl ester were used to carry out batch experiments.     

Enantiomeric Neolignans and a Sesquiterpene from Solanum erianthum and Their Absolute Configuration Assignment

One pair of new C‐8–C‐3′/C‐7–O–C‐4′ linked neolignan enantiomers ( 1a / 1b ) and one new guaiane sesquiterpene ( 2 ) first featuring the 1(2),9(10)‐conjugated double bond were isolated from the stems of Solanum erianthum (Solanceae). Their structures were characterized on the basis of extensive spectroscopic analyses, especially from their 2D nuclear magnetic resonance (NMR) spectra. The absolute configurations of 1a / 1b were rigorously elucidated by electronic circular dichroism (ECD) experiments combined with the reversed helicity rule for the 2,3‐dihydrobenzo[b]furan chromophore, and compound 2 is the first report on the sterochemical assignment of a guaiane sesquiterpene by using the allylic axial chirality rule for the conjugated diene chromophore in combination with the calculated ECD spectrum. Chirality 28:259–263, 2016. © 2016 Wiley Periodicals, Inc.     

Asymmetric Allylation of α‐Ketoester‐Derived N‐Benzoylhydrazones Promoted by Chiral Sulfoxides/N‐Oxides Lewis Bases: Highly Enantioselective Synthesis of Quaternary α‐Substituted α‐Allyl‐α‐Amino Acids

Chiral sulfoxides/N‐oxides (R)‐ 1 and (R,R)‐ 2 are effective chiral promoters in the enantioselective allylation of α‐keto ester N‐benzoylhydrazone derivatives 3a , 3b , 3c , 3d , 3e , 3f , 3g to generate the corresponding N‐benzoylhydrazine derivatives 4a , 4b , 4c , 4d , 4e , 4f , 4g , with enantiomeric excesses as high as 98%. Representative hydrazine derivatives 4a , 4b were subsequently treated with SmI₂, and the resulting amino esters 5a , 5b with LiOH to obtain quaternary α‐substituted α‐allyl α‐amino acids 6a , 6b , whose absolute configuration was assigned as (S), with fundament on chemical correlation and electronic circular dichroism (ECD) data. Chirality 25:529–540, 2013. © 2013 Wiley Periodicals, Inc.     

Identification of a flavin‐containing S‐oxygenating monooxygenase involved in alliin biosynthesis in garlic

S‐Alk(en)yl‐l ‐cysteine sulfoxides are cysteine‐derived secondary metabolites highly accumulated in the genus Allium. Despite pharmaceutical importance, the enzymes that contribute to the biosynthesis of S‐alk‐(en)yl‐l ‐cysteine sulfoxides in Allium plants remain largely unknown. Here, we report the identification of a flavin‐containing monooxygenase, AsFMO1, in garlic (Allium sativum), which is responsible for the S‐oxygenation reaction in the biosynthesis of S‐allyl‐l ‐cysteine sulfoxide (alliin). Recombinant AsFMO1 protein catalyzed the stereoselective S‐oxygenation of S‐allyl‐l ‐cysteine to nearly exclusively yield (R_CS_S)‐S‐allylcysteine sulfoxide, which has identical stereochemistry to the major natural form of alliin in garlic. The S‐oxygenation reaction catalyzed by AsFMO1 was dependent on the presence of nicotinamide adenine dinucleotide phosphate (NADPH) and flavin adenine dinucleotide (FAD), consistent with other known flavin‐containing monooxygenases. AsFMO1 preferred S‐allyl‐l ‐cysteine to γ‐glutamyl‐S‐allyl‐l ‐cysteine as the S‐oxygenation substrate, suggesting that in garlic, the S‐oxygenation of alliin biosynthetic intermediates primarily occurs after deglutamylation. The transient expression of green fluorescent protein (GFP) fusion proteins indicated that AsFMO1 is localized in the cytosol. AsFMO1 mRNA was accumulated in storage leaves of pre‐emergent nearly sprouting bulbs, and in various tissues of sprouted bulbs with green foliage leaves. Taken together, our results suggest that AsFMO1 functions as an S‐allyl‐l ‐cysteine S‐oxygenase, and contributes to the production of alliin both through the conversion of stored γ‐glutamyl‐S‐allyl‐l ‐cysteine to alliin in storage leaves during sprouting and through the de novo biosynthesis of alliin in green foliage leaves.     

Isolation and characterisation of bacterial strains containing enantioselective DMSO reductase activity: application to the kinetic resolution of racemic sulfoxides

The kinetic resolution of racemic sulfoxides by dimethyl sulfoxide (DMSO) reductases was investigated with a range of microorganisms. Three bacterial isolates (provisionally identified as Citrobacter braakii, Klebsiella sp. and Serratia sp.) expressing DMSO reductase activity were isolated from environmental samples by anaerobic enrichment with DMSO as terminal electron acceptor. The organisms reduced a diverse range of racemic sulfoxides to yield either residual enantiomer depending upon the strain used. C. braakii DMSO-11 exhibited wide substrate specificity that included dialkyl, diaryl and alkylaryl sulfoxides, and was unique in its ability to reduce the thiosulfinate 1,4-dihydrobenzo-2, 3-dithian-2-oxide. DMSO reductase was purified from the periplasmic fraction of C. braakii DMSO-11 and was used to demonstrate unequivocally that the DMSO reductase was responsible for enantiospecific reductive resolution of racemic sulfoxides.     

Neuroprotective effects of (E)-3,4-diacetoxystyryl sulfone and sulfoxide derivatives in vitro models of Parkinson's disease

(E)-3,4-dihydroxystyryl aralkyl sulfones and sulfoxides have been reported as novel multifunctional neuroprotective agents in previous studies, which as phenolic compounds display antioxidative and antineuroinflammatory properties. To further enhance the neuroprotective effects and study structure-activity relationship of the derivatives, we synthesized their acetylated derivatives, (E)-3,4-diacetoxystyryl sulfones and sulfoxides, and examined their neuroprotective effects in vitro models of Parkinson’s disease. The results indicate that (E)-3,4-diacetoxystyryl sulfones and sulfoxides can significantly inhibit kinds of neuron cell injury induced by toxicities, including 6-OHDA, NO, and H₂O₂. More important, they show higher antineuroinflammatory properties and similar antioxidative properties to corresponding un-acetylated compounds. Thus, we suggest that (E)-3,4-diacetoxystyryl sulfones and sulfoxides may have potential for the treatment of neurodegenerative disorders, especially Parkinson’s disease.     

The influence of protective groups on diastereofacial selectivity of Diels-Alder cycloaddition reactions

The diastereofacial selectivity of both inter- and intramolecular Diels-Alder reactions with dienes having an allylic stereogenic center has been studied by varying the allylic oxygen protective group. Four different hydroxy protective groups were investigated including benzyl, t-butyldiphenylsilyl, triethylsilyl, and t-butyldimethylsilyl ethers. For intermolecular reactions, the benzyl ether derivative gave the highest sπ-facial selectivity through a transition state in which the allylic stereocenter favors the CH eclipsed conformation. For intramolecular cycloadditions, the t-butyldimethylsilyl group gave a slightly higher selectivity than the benzyl ether derivative through a transition state in which the allylic stereocenter favors the CO eclipsed conformation. The opposite diastereofacial selectivity observed for inter- and intramolecular reactions is explained by considering both steric and electronic effects. © 1995 Wiley-Liss, Inc.     

Enantioselective epoxidation by an optically active hydroperoxide

Enantioselective epoxidation of prochiral allylic alcohols with optically active 4,6-di-O-acetyl-2,3-dideoxy-α-D -threo-hex-2-enopyranosyl hydroperoxide in the presence of Ti(O-i-Pr)₄ gives chiral epoxy alcohols with moderate enantiomeric excess. © 1993 Wiley-Liss, Inc.     

Relation between Neutral Lipid Accumulation and the Growth Phase in the Yeast,Lipomyces starkeyi,a Fat Producing Yeast

In order to investigate the substrate binding feature of undecaprenyl diphosphate synthase from Micrococcus luteus B-P 26 with respect to farnesyl diphosphate and a reaction intermediate, (Z,E,E)-geranylgeranyl diphosphate, we examined the reactivity of artificial substrate analogs, 3-desmethyl farnesyl diphosphate and 3-desmethyl Z-geranylgeranyl diphosphate, which lack the methyl group at the 3-position of farnesyl diphosphate and Z-geranylgeranyl diphosphate, respectively. Undecaprenyl diphosphate synthase did not accept either of the 3-desmethyl analogs as the allylic substrate, indicating that the methyl group at the 3-position of the allylic substrate is important in the undecaprenyl diphosphate synthase reaction. These analogs showed different inhibition patterns in the cis-prenyl chain elongation reaction with respect to the reactions of farnesyl diphosphate and Z-geranylgeranyl diphosphate as allylic substrate. These results suggest that the binding site for the natural substrate farnesyl diphosphate and those for the intermediate allylic diphosphate, which contains the cis-prenyl unit, are different during the cis-prenyl chain elongation reaction.     

Growth, sex differentiation and gonad and plasma levels of sex steroids in male‐ and female‐dominant populations of Dicentrarchus labrax obtained through repeated size grading

Starting from 66 days post hatching (dph), European sea bass Dicentrarchus labrax were graded successively to create a fast growing (L‐extreme) and a slow growing (S‐extreme) population. The L‐extreme population grew significantly larger (ANOVA, n = 89–101, P < 0·01) attaining twice the wet mass of the S‐extreme population at 300 dph (130·9 ± 1·8 v. 66·7 ± 0·9 g, mean ± s .e .). When the two populations were sexed, the L‐extreme consisted of 96·5% and the S‐extreme of 30·2% females, while the ungraded control had 59·2% females. Sex differentiation began first in females at a total length (L_T) of 97 ± 4 mm and wet mass of 9·4 ± 1·2 g (150 dph), and was completed when fish reached 166 ± 6 mm and 53·4 ± 6·4 g (250 dph) in both sexes. Precocious maturation in males was positively correlated to growth. Gonad oestradiol (E₂) was significantly higher in the female‐dominant population at the onset of ovarian differentiation (ANOVA, n = 10, P < 0·05) and in the plasma after the appearance of the first primary oocytes (P < 0·01). Gonad testosterone (T) increased in both populations after sex differentiation (ANOVA, n = 10, P < 0·05), while plasma levels were significantly higher in the male‐dominant population (P < 0·001). Both gonad and plasma 11‐keto testosterone (11‐KT) were significantly higher in the male‐dominant population (ANOVA, n = 10, P < 0·01) reaching maximal values at spermiation. The results suggest that E₂ is closely related with ovarian differentiation and the onset of oogenesis, while T and 11‐KT is more related to spermatogenesis and precocious maturation.     

Changes in growth and maturation parameters of Pacific sardine Sardinops sagax collected off California during a period of stock recovery from 1994 to 2010

Whether fluctuation in density influenced the growth and maturation variables of three aggregated cohorts (fish born during the 1986–1993, 1996–2003 and 2004–2008 periods) of Pacific sardine Sardinops sagax caeruleus collected off the Californian coast from 2004 to 2010 was investigated. Using a von Bertalanffy mixed‐effects model with aggregated cohorts as covariates, estimated growth rate significantly covaried with aggregated cohorts. Growth rate (K) was modelled as a fixed effect and estimated to be 0·264 ± 0·015 (±s.e ). Statistical contrasts among aggregated cohorts showed that the 1996–2003 cohorts had a significantly lower growth rate than the other two aggregated cohorts. The theoretical age at length zero (t₀) and the standard length at infinity (L_S∞) were modelled as random effects, and were estimated to be ?2·885 ± 0·259 (±s.e ) and 273·13 ± 6·533 mm (±s.e ). The relation of ovary‐free mass at length was significantly different among the three aggregated cohorts, with the allometric coefficient estimated to be 2·850 ± 0·013 (±s.e ) for the S. sagax population. The age‐at‐length trajectory of S. sagax born between 1986 and 2008 showed strong density dependence effects on somatic growth rates. In contrast to the density‐dependent nature of growth, the probability to be mature at‐size or at‐age was not significantly affected by aggregated cohort density. The size and the age‐at‐50% maturity were estimated to be 150·92 mm and 0·56 years, respectively. Stock migration, natural fluctuations in biomass and removal of older and larger S. sagax by fishing might have been interplaying factors controlling growth parameters during 1986–2010.     

Hydrolysis of polyethyleneterephthalate by p‐nitrobenzylesterase from Bacillus subtilis

From a screening on agar plates with bis(benzoyloxyethyl) terephthalate (3PET), a Bacillus subtilis p‐nitrobenzylesterase (BsEstB) was isolated and demonstrated to hydrolyze polyethyleneterephthalate (PET). PET‐hydrolase active strains produced clearing zones and led to the release of the 3PET hydrolysis products terephthalic acid (TA), benzoic acid (BA), 2‐hydroxyethyl benzoate (HEB), and mono‐(2‐hydroxyethyl) terephthalate (MHET) in 3PET supplemented liquid cultures. The 3PET‐hydrolase was isolated from non‐denaturating polyacrylamide gels using fluorescein diacetate (FDA) and identified as BsEstB by LC‐MS/MS analysis. BsEstB was expressed in Escherichia coli with C‐terminally fused StrepTag II for purification. The tagged enzyme had a molecular mass of 55.2 kDa and a specific activity of 77 U/mg on p‐nitrophenyl acetate and 108 U/mg on p‐nitrophenyl butyrate. BsEstB was most active at 40°C and pH 7.0 and stable for several days at pH 7.0 and 37°C while the half‐life times decreased to 3 days at 40°C and only 6 h at 45°C. From 3PET, BsEstB released TA, MHET, and BA, but neither bis(2‐hydroxyethyl) terephthalate (BHET) nor hydroxyethylbenzoate (HEB). The k_cat values decreased with increasing complexity of the substrate from 6 and 8 (s?1) for p‐nitrophenyl‐acetate (4NPA) and p‐nitrophenyl‐butyrate (4NPB), respectively, to 0.14 (s?1) for bis(2‐hydroxyethyl) terephthalate (BHET). The enzyme hydrolyzed PET films releasing TA and MHET with a concomitant decrease of the water‐contact angle (WCA) from 68.2° ± 1.7° to 62.6° ± 1.1° due to formation of novel hydroxyl and carboxyl groups. These data correlated with a fluorescence emission intensity increase seen for the enzyme treated sample after derivatization with 2‐(bromomethyl)naphthalene. © 2011 American Institute of Chemical Engineers Biotechnol. Prog., 2011