Carotenoids with a 5,6-dihydro-5,6-dihydroxy-beta-end group, from yellow sweet potato "Benimasari", Ipomoea batatas Lam

A series of carotenoids with a 5,6-dihydro-5,6-dihydroxy-beta-end group, named ipomoeaxanthins A (1), B (2), C1 (3) and C2 (4) were isolated from the flesh of yellow sweet potato "Benimasari", Ipomoea batatas Lam. Their structures were determined to be (5R,6S,3'R)-5,6-dihydro-beta,beta-carotene-5,6,3'-triol (1), (5R,6S,5'R,6'S)-5,6,5',6'-tetrahydro-beta,beta-carotene-5,6,5'6'-tetrol (2), (5R,6S,5'R,8'R)-5',8'-epoxy-5,6,5',8'-tetrahydro-beta,beta-carotene-5,6-diol (3), and (5R,6S,5'R,8'S)-5',8'-epoxy-5,6,5',8'-tetrahydro-beta,beta-carotene-5,6-diol (4) by UV-Vis, NMR, MS and CD data.     

Dibenzylbutane and aryltetralone lignans from seeds of Virola sebifera

Two lignans rel-(8R, 8'R)-3,4:3',4'-bis-(methylenedioxy)-7.7'-dioxo-lignan and (7'R,8'S,8S)-2'-hydroxy-3,4:4',5'-bis-(methylenedioxy)-7-oxo-2,7'-cyclolignan were isolated from seeds of Virola sebifera. The cyclolignan showed two atropisomers as determined by 1H NMR spectroscopy at low temperature.     

Partial synthesis of serum carotenoids and their metabolites

Human serum and tissues contain in excess of 12 dietary carotenoids and several metabolites that originate from consumption of fruits and vegetables. Among these are hydroxycarotenoids: (3R,3'R,6'R)-lutein (1), (3R,3'R)-zeaxanthin (2), (3R,6'R)-α-cryptoxanthin (3), and (3R)-β-cryptoxanthin (4). In addition, several dehydration products of 1 have also been identified in human serum, these are: (3R,6'R)-3-hydroxy-3',4'-didehydro-β,γ-carotene (5), (3R,6'R)-3-hydroxy-2',3'-didehydro-β,ε-carotene (6), and (3R)-3-hydroxy-3',4'-didehydro-β,β-carotene (7). Several metabolites of 1 and/or 2, namely, (3R,3'S,6'R)-lutein (3'-epilutein, 8) and (3R,3'S;meso)-zeaxanthin (9) have also been characterized in human serum and ocular tissues. Semi-synthetic processes have been developed that separately transform commercially available 1 into 4 via 7 as well as 1 into 8. While 8 is converted into 2 by base-catalyzed isomerization, 7 is transformed into 2 and its (3R,3'S;meso)-stereoisomer (9) by regioselective hydroboration.     

Trypanocidal tetrahydrofuran lignans from inflorescences of Piper solmsianum

In addition to sitosterol, syringaldehyde, 3,4,5-trimethoxybenzoic acid, isoelemicin and grandisin, two new tetrahydrofuran lignans were isolated from Piper solmsianun and characterized as rel-(7R,8R,7'R,8'R)-3',4'-methylenedioxy-3,4,5,5'-tetramethoxy-7,7'-epoxylignan and rel-(7R,8R,7'R,8'R)-3,4,3',4'-dimethylenedioxy-5,5'-dimethoxy-7,7'-epoxylignan on the basis of spectroscopic data, including 2D NMR spectrometric techniques. Their in vitro activity were determined against the trypomastigote form of Trypanossoma cruzi.     

Antioxidant lignans from Larrea tridentata

Three lignans, (7S,8S,7'S,8'S)-3,3',4'-trihydroxy-4-methoxy-7,7'-epoxylignan, meso-(rel 7S,8S,7'R,8'R)-3,4,3',4'-tetrahydroxy-7,7'-epoxylignan, and (E)-4,4'-dihydroxy-7,7'-dioxolign-8(8')-ene, together with 10 known compounds, were isolated from the leaves of Larrea tridentata. The structures of the new compounds were determined primarily from 1D and 2D NMR spectroscopic analysis. Their antioxidant activities against intracellular reactive oxygen species were evaluated in HL-60 cells.     

Is methyl-branching in alpha-tocopherol's "tail" important for its in vivo activity? Rat curative myopathy bioassay measurements of the vitamin E activity of three 2RS-n-alkyl-2,5,7,8-tetramethyl-6-hydroxychromans

The vitamin E activity of the acetates of three 2RS-n-alkyl-2,5,7,8-tetramethyl-6-hydroxychroman analogs of alpha-tocopherol have been measured and compared directly with all-rac-alpha-tocopheryl acetate, or indirectly via 2R,4'R,8'R-alpha-tocopheryl acetate, using the rat curative myopathy, plasma pyruvate kinase assay. The analogs with alkyl chain lengths of 11 and 13 carbons have activities which not only do not differ significantly (p greater than 0.05) from each other but also do not differ from that of all-rac-alpha-tocopheryl acetate. This finding indicates that methyl branching in the phytyl tail at the 4', 8', and 12' positions has little if any influence upon vitamin E activity. Thus physical interactions involving the methyl branches of the phytyl tail and the polyunsaturated moieties of membrane phospholipids are unimportant in vivo, insofar as this bioassay is concerned. However, the length of the hydrocarbon tail is important. This is indicated by the result obtained with the acetate of the analog with an alkyl chain length of 15 carbon atoms which had only 15% of the activity of 2R,4'R,8'R-alpha-tocopheryl acetate, i.e., 22% of the activity of all-rac-alpha-tocopheryl acetate since this form is 1.47 times less active than 2R,4'R,8'R-alpha-tocopheryl acetate in the curative myopathy bioassay (Weiser, Vecchi, & Schlachter, Internat. J. Vit. Nutr. Res. 55:149-158, 1985).     

Asymmetrical ligand binding by abscisic acid 8'-hydroxylase

Abscisic acid (ABA), a plant stress hormone, has a chiral center (C1') in its molecule, yielding the enantiomers (1'S)-(+)-ABA and (1'R)-(-)-ABA during chemical synthesis. ABA 8'-hydroxylase (CYP707A), which is the major and key P450 enzyme in ABA catabolism in plants, catalyzes naturally occurring (1'S)-(+)-enantiomer, whereas it does not recognize naturally not occurring (1'R)-(-)-enantiomer as either a substrate or an inhibitor. Here we report a structural ABA analogue (AHI1), whose both enantiomers bind to recombinant Arabidopsis CYP707A3, in spite of stereo-structural similarity to ABA. The difference of AHI1 from ABA is the absence of the side-chain methyl group (C6) and lack of the alpha,beta-unsaturated carbonyl (C2'C3'-C4'O) in the six-membered ring. To explore which moiety is responsible for asymmetrical binding by CYP707A3, we synthesized and tested ABA analogues that lacked each moiety. Competitive inhibition was observed for the (1'R) enantiomers of these analogues in the potency order of (1'R,2'R)-(-)-2',3'-dihydro-4'-deoxo-ABA (K(I)=0.45 microM)>(1'R)-(-)-4'-oxo-ABA (K(I)=27 microM)>(1'R)-(-)-6-nor-ABA and (1'R,2'R)-(-)-2',3'-dihydro-ABA (no inhibition). In contrast to the (1'R)-enantiomers, the inhibition potency of the (1'S)-analogues declined with the saturation of the C2',C3'-double bond or with the elimination of the C4'-oxo moiety. These findings suggest that the C4'-oxo moiety coupled with the C2',C3'-double bond is the significant key functional group by which ABA 8'-hydroxylase distinguishes (1'S)-(+)-ABA from (1'R)-(-)-ABA.     

Carbocyclic 5'-noruridine

A convenient preparation of (1'R,2'S,3'R,4'S)-1-(2',3',4'-trihydroxycyclopent-1'-yl)-1H-uracil (carbocyclic 5'-noruridine, 1) is described in 2 steps from the palladium complex of (+)-(1R,4S)-4-hydroxy-2-cyclopenten-1-yl acetate (3) and the sodium salt of uracil (2). Compound 1 was sought as a previously unknown member of the series of carbocyclic 5'-nor nucleosides needed as moieties for new oligomers. With 1 available, its antiviral properties and those of its enantiomer (5) are reported with 5 showing promising activity towards Epstein-Barr virus.     

Sphingolipids with neuritogenic activity from Euphorbia sororia

Two groups of sphingolipids 1 and 2 were isolated from the aerial parts of Euphorbia sororia. On the basis of spectroscopic data, chemical methods and GC-MS analysis, the structures of 1 and 2 were characterized as 1-O-beta-D-glucopyranosyl-(2S,3S,4R,8Z)-2-[(2'R)-2'-hydroxydocosanoyl approximately hexacosanoyl, octacosanoyl amino]-1,3,4-octadecanetriol-8-ene and (2S,3S,4R,8E)-2-[(2'R)-2'-hydroxyeicosanoyl approximately hexacosanoyl amino]-1,3,4-octadecanetriol-8-ene, respectively. Both of them exhibited marked neuritogenic activity on the rat pheochromocytoma PC12 cell line.     

Expression of functional mGlu5 metabotropic glutamate receptors in human melanocytes

Cultured human melanocytes express mGlu5 metabotropic glutamate (mGlu) receptors, as shown by RT-PCR, immunocytochemistry, Western blot analysis, and measurement of agonist-stimulated polyphosphoinositide hydrolysis. The mGlu5 receptor agonists (S)-3, 5-dihydroxyphenylglycine and quisqualate increased [(3)H-methyl]thymidine incorporation and melanocyte proliferation in subconfluent cultures, but impaired cell viability in confluent cultures. Both effects were prevented by 2-methyl-6-(2-phenyl-1-ethynyl)-pyridine, a potent and highly selective mGlu5 receptor antagonist. Agonists of other mGlu receptor subtypes (such as the mGlu2/3 receptor agonist, 2S,2'R,3'R-2-2', 3'-dicarboxycyclopropylglycine, or the mGlu4/6/7/8 receptor agonist, L-2-amino-4-phosphonobutanoate) or selective agonists of ionotropic glutamate receptors (N-methyl-D-aspartate, alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate, and kainate) did not affect melanocyte proliferation or viability. The presence of a receptor for glutamate, the major excitatory neurotransmitter, in human melanocytes is intriguing. mGlu5 receptors may be involved in the control of melanocyte proliferation (and perhaps in other functions), but harbor a potential toxicity and may therefore contribute to cell damage under pathological conditions.     

A-hydroxyphosphonate oligonucleotides: a promising DNA type?

The synthesis of monomers (S)-1, (R)-1 and 2 derived from (5'S)-, (5'R)-2'-deoxythymidine-5'-C-phosphonic acids and 2',5'-dideoxythymidine-5'-C-phosphonic acids was elaborated. The protection of the 5'-hydroxyl by the methoxycarbonyl group was a key step of the synthesis. Prepared monomers were used for the solid-phase assembly of several types oligothymidylate 15-mers (S)-3, (S)-4, (S)-5, (R)-4 and (R)-5 containing the chiral 3'-O-P-CH(OH)-5' internucleotide linkage. Their hybridization properties with dA15 and rA15 were studied as well as their resistance against nuclease cleavage.     

Configurational analysis of cubebins and bicubebin from Aristolochia lagesiana and Aristolochia pubescens

(8S,8'R,9S)-, (8R,8'R,9R)-, and (8R,8'R,9S)-cubebins, together with (8R,8'R,8'R,8'R,9R,9'S)-bicubebin, were isolated from Aristolochia lagesiana and Aristolochia pubescens. Their structures were determined by spectroscopic methods, including 1H and 13C NMR spectroscopy at low temperatures, and by chemical transformations.     

The stereochemistry of trans-4-hydroxynonenal-derived exocyclic 1,N2-2'-deoxyguanosine adducts modulates formation of interstrand cross-links in the 5'-CpG-3' sequence

The trans-4-hydroxynonenal (HNE)-derived exocyclic 1, N(2)-dG adduct with (6S,8R,11S) stereochemistry forms interstrand N(2)-dG-N(2)-dG cross-links in the 5'-CpG-3' DNA sequence context, but the corresponding adduct possessing (6R,8S,11R) stereochemistry does not. Both exist primarily as diastereomeric cyclic hemiacetals when placed into duplex DNA [Huang, H., Wang, H., Qi, N., Kozekova, A., Rizzo, C. J., and Stone, M. P. (2008) J. Am. Chem. Soc. 130, 10898-10906]. To explore the structural basis for this difference, the HNE-derived diastereomeric (6S,8R,11S) and (6R,8S,11R) cyclic hemiacetals were examined with respect to conformation when incorporated into 5'-d(GCTAGC XAGTCC)-3' x 5'-d(GGACTCGCTAGC)-3', containing the 5'-CpX-3' sequence [X = (6S,8R,11S)- or (6R,8S,11R)-HNE-dG]. At neutral pH, both adducts exhibited minimal structural perturbations to the DNA duplex that were localized to the site of the adduction at X(7) x C(18) and its neighboring base pair, A(8) x T(17). Both the (6S,8R,11S) and (6R,8S,11R) cyclic hemiacetals were located within the minor groove of the duplex. However, the respective orientations of the two cyclic hemiacetals within the minor groove were dependent upon (6S) versus (6R) stereochemistry. The (6S,8R,11S) cyclic hemiacetal was oriented in the 5'-direction, while the (6R,8S,11R) cyclic hemiacetal was oriented in the 3'-direction. These cyclic hemiacetals effectively mask the reactive aldehydes necessary for initiation of interstrand cross-link formation. From the refined structures of the two cyclic hemiacetals, the conformations of the corresponding diastereomeric aldehydes were predicted, using molecular mechanics calculations. Potential energy minimizations of the duplexes containing the two diastereomeric aldehydes predicted that the (6S,8R,11S) aldehyde was oriented in the 5'-direction while the (6R,8S,11R) aldehyde was oriented in the 3'-direction. These stereochemical differences in orientation suggest a kinetic basis that explains, in part, why the (6S,8R,11S) stereoisomer forms interchain cross-links in the 5'-CpG-3' sequence whereas the (6R,8S,11R) stereoisomer does not.     

Synthesis and cardiovascular activity of metoprolol analogues

The synthesis of four novel analogues of metoprolol, a well-known beta1-blocker used to reduce arterial blood pressure, is described. The preparation of (2S,2'S)-7, (2R,2'S)-7, (2R,2'R)-8, and (2S,2'R)-8 was based on the reaction of racemic 2-[4-(2'-methoxyethyl)-phenoxymethyl]-oxirane (4) with (R)- or (S)-2-amino-1-butanol. Salient characteristics of analogues 7 and 8 relative to metoprolol are the incorporation of an additional stereogenic center, as well as a methyl group and a hydroxyl function on the nitrogen-containing chain. These novel derivatives present significant hypotensive and bradycardiac activity, although no blocking action toward beta1 and beta2 adrenergic receptor.     

Oxygenated lycopene and dehydrated lutein in tomato puree

Oxygenated lycopenes, (2S*,5S*,6R*)-2,6-cyclolycopene-1-methoxy-5-ol, (2S*,5S*,6R*)-1,16-didehydro-2,6-cyclolycopene-5-ol and (3R,6'R)-3-hydroxy-3',4'-didehydro-beta,gamma-carotene (anhydrolutein I) were isolated from tomato puree. The structures of these compounds were elucidated on the basis of spectroscopic evidence.     

Absolute configuration of antifibrotic (+)-episesamin isolated from Lindera obtusiloba BLUME

Fractionation of a 70% ethanolic extract from twigs of Lindera obtusiloba BLUME (Japanese spicebush, Tohaku) yielded five fractions of different polarity. The antifibrotic activity within the chloroform phase was best assessed by an in vitro bioassay using rat hepatic stellate cell (HSC) proliferation and their autocrine transforming growth factor beta (TGF-beta) expression as sensitive fibrosis-associated read out. Chromatography of the chloroform extract on Sephadex LH-20 or liquid-liquid extractions yielded a crystalline compound as an active principle, which was identified from NMR and ESI-MS analyses, its melting point, and its optical rotation as (7S,7'R,8R,8'R)-3,4:3',4'-bis(methylenedioxy)-7,9':7',9-diepoxy-lignane [(+)-episesamin]. X-Ray diffraction confirmed the structure and provided, for the first time, directly its absolute configuration. (+)-Episesamin blocked proliferation and the profibrotic autocrine TGF-beta expression HSC without significant cytotoxicity.     

alpha-Glucosidase inhibitory constituents from stem bark of Terminalia superba (Combretaceae)

The CH(2)Cl(2)/CH(3)OH (1/1) extract of the dried stem bark of Terminalia superba afforded two compounds, (7S,8R,7'R,8'S)-4'-hydroxy-4-methoxy-7,7'-epoxylignan and meso-(rel 7S,8R,7'R,8'S)-4,4'-dimethoxy-7,7'-epoxylignan along with 11 known compounds. The structures of the compounds were established by analysing the spectroscopic data and also comparing it with the data of previously known analogues. All the isolated compounds were evaluated for their glycosidase inhibition activities. Gallic acid and methyl gallate showed significant alpha-glucosidase inhibition activity.     

Biological and conformational studies of [Val4]morphiceptin and [D-Val4]morphiceptin analogs incorporating cis-2-aminocyclopentane carboxylic acid as a peptidomimetic for proline

We report the synthesis, biological activity, and conformational analysis of tetrapeptide analogs related to [Val4]morphiceptin and [D-Val4]morphiceptin in which the proline at the second position has been replaced with cis-2-aminocyclopentane carboxylic acid (cis-2-Ac5c). Since the cis-2-Ac5c residue contains a normal amide, only the trans form has been observed about the amide bond between the first and second residues. The cis-2-Ac5c is a beta amino acid with two chiral centers resulting in two possible configurational isomers, namely (1S, 2R) and 1R, 2S) forms. The analogs containing the (1S, 2R)-Ac5c residue show activity at the mu-receptor but are inactive at the delta-receptor, resulting in a high selectivity for the mu-receptor. The (1R,2S)-Ac5c containing analogs are completely inactive at both the mu- and delta-receptors. The conformational analysis indicates that the separation of the aromatic rings of the tyrosine and phenylalanine residues, as expressed by the center-to-center distance, is 10.1-12.7 A for the preferred conformations of the bioactive analogs containing the (1S,2R)-Ac5c residue while a range of 4.8-7.0 A is observed for the preferred conformations of the inactive analogs with the (IR,2S)-Ac5c residue. A comparison of the findings from the conformational analysis and biological assays establishes the fact that a relatively large separation of the two aromatic side chains is required for the mu-opioid receptor activity of these molecules. Since the tetrapeptide amides studied in this investigation show similar biological profiles to those of the morphiceptin-related analogs, we have compared the preferred conformations estimated for the cis-2-Ac5c containing analogs with those of morphiceptin. One of the low energy conformations calculated for morphiceptin with the cis form about the tyrosine and proline residues has considerable topological similarity with the bioactive analogs containing the (1S,2R)-Ac5c residue, indicating that the cis from about these two residues is required for the biological activity of the morphiceptin-related analogs containing the proline at the second position.     

Reversible cleavage of the cobalt-carbon bond to coenzyme B12 catalysed by methylmalonyl-CoA mutase from Propionibacterium shermanii. The use of coenzyme B12 stereospecifically deuterated in position 5'

1. (5'R)-(5'-2H1)Adenosine [(5'R):(5'S) = 85:15] was prepared by a procedure which involved inter alia the reduction of 6-N-benzoyl-2',3'-O-isopropylidene-5'-oxoadenosine with a reagent obtained from LiAl2H4 and (-)-isoborneol. 2. (5'S)-(5'-2H1)AdoCbl [(5'S):(5'R) = 74:26] (AdoCbl = 5'-deoxyadenosylcobalamin) was synthesized by reacting cobal(I)amin with (5'R)-2'-3'-O-isopropylidene-5'-tosyl-(5'-2H1) adenosine followed by acid hydrolysis to remove the isopropylidene protective group. 3. (5'R)-(5'-2H1)AdoCbl [(5'R):(5'S) = 77:23] was prepared by reacting cobalt(I)amin with (5'S)-5'-chloro-5'-(5'-2H1)deoxyadenosine [(5'S):(5'R) = 80:20] obtained in turn from (5'R)-(5'-2H1)adenosine. The reaction sequence involved two consecutive inversions at the C-5' atom of adenosine 4. Comparison of the 500-MHz 1H-NMR spectra of unlabelled, (5'S)- and (5'R)-(5'-2H1)AdoCbl allowed assignment of the triplet at 0.58 ppm and the doublet at 1.525 ppm to the diastereotopic 5'-HRe and 5'-HSi atoms, respectively. On acidification, these two protons gave rise to two triplets at 0.11 ppm and 1.78 ppm indicating that torsion had occurred around the C-4'--C-5' bond. 5. Samples of (5'R)- and (5'S)-(5'-2H1)AdoCbl were incubated with methylmalonyl-CoA mutase from Propionibacterium shermanii. Examination by 1H-NMR spectroscopy at 500 MHz revealed partial loss and stereochemical scrambling of the deuterium at the 5' position. This indicates transient conversion of the C-5' atom into a torsiosymmetric group and hence cleavage of the cobalt-carbon bond during interaction with the enzyme. The mechanism by which deuterium is lost remains to be elucidated.