Optical bleaching front in bedrock revealed by spatially-resolved infrared photoluminescence

Optically stimulated luminescence (OSL) dating of sediment, based on the accumulation of trapped charge in natural crystals since their last exposure to daylight, has revolutionised our understanding of the late Quaternary period. Recently, a complementary technique called luminescence rock surface dating (RSD), which uses differential spatial eviction of trapped charges in rocks exposed to daylight, has been developed to derive exposure and burial ages, and hard-rock erosion rates. In its current form, the RSD technique suffers from labour intensive sample preparation, uncertainties in the depth and dose rate estimates, and poor resolution of the luminescence-depth profile. Here, we develop a novel, 2D luminescence imaging technique for RSD of large rock slabs (3 × 5 cm) to overcome these challenges. We utilize the recently discovered infrared photoluminescence (IRPL) signal for direct, non-destructive imaging of the luminescence-depth profile in a sub-aerially exposed granitic rock, with an unprecedented spatial resolution of ~140 µm. We further establish a correlation between luminescence and geochemistry using micro X-ray fluorescence (µXRF) spectroscopy. Our study promises a substantial advancement in luminescence imaging and paves the path towards novel applications using 2D dating, micro-dosimetry in mixed composition samples, and portable instrumentation for in-situ luminescence measurements.

Protective effects of new antioxidant compositions of 4-methylcoumarins and related compounds with dl-α-tocopherol and l-ascorbic acid

BACKGROUND

Coumarin derivatives possess a wide range of biological activities. By functionalization of the parent coumarin skeleton that has neither antioxidant nor biological activity, a series of new bio-antioxidants has been designed.

RESULTS

New antioxidant compositions (equimolar binary and ternary mixtures) of eight 4-methylcoumarins and three related compounds have been tested and different effects between individual components have been observed: synergism (positive effect), additivism (summary effect) and antagonism (negative effect). Higher oxidative stability of the lipid substrate was obtained in the presence of the new antioxidant compositions of the studied compounds with dl-α-tocopherol and l-ascorbic acid. The role of each component in the antioxidant compositions of ternary mixtures has been identified by using new equations composed by the authors.

CONCLUSION

All ternary mixtures demonstrate synergism as a result of continuous regeneration of dl-α-tocopherol from the studied antioxidants and l-ascorbic acid. Theoretical calculations have been probed as indicators of the expected effects between the individual components in a binary mixture. © 2018 Society of Chemical Industry.

Synthesis of novel 3'-azido-3'-deoxy-α-L-ribo configured nucleosides: A comparative study between chemical and chemo-enzymatic methodologies

Syntheses of novel 3'-azido-3'-deoxy-2'-O,4'-C-methylene-α-L-ribofuranosyl nucleosides have been carried out from 3'-azido-3'-deoxy-4'-C-hydroxymethyl-β-D-xylofuranosyl nucleosides following both chemical and chemo-enzymatic methodologies. The precursor nucleoside in turn was synthesized from a common glycosyl donor 4-C-acetoxymethyl-1,2,5-tri-O-acetyl-3-azido-3-deoxy-α,β-D-xylofuranose, which was obtained by the acetolysis of 4-C-acetoxymethyl-5-O-acetyl-3-azido-3-deoxy-1,2-O-isopropylidene-α-D-xylofuranose in 96% yield. It has been observed that a chemo-enzymatic pathway for the synthesis of targeted nucleosides is much more efficient than a chemical pathway, leading to the improvement in yield for the synthesis of 3'-azido-3'-deoxy-α-L-ribofuranosyl thymine and uracil from 49 to 89% and 55 to 93%, respectively.

Synthesis and biological properties of triazole-linked locked nucleic acid

We have synthesized and studied the biological and biophysical properties of triazole-linked ribo and xylo locked nucleic acid (LNA). The combination of LNA with the Isobe triazole linkage gave high binding affinity when incorporated at the 3' or 5' termini of oligonucleotides, but low binding affinity at internal positions. Antisense oligonucleotides (ASOs) and siRNAs containing triazole dimers were highly active and nuclease resistant. Surprisingly, the xyloLNA-modified siRNA was the most active of the series.

Mono and dihydroxy coumarin derivatives: Copper chelation and reduction ability

Due to the limited array of the currently available copper chelators, research of such compounds continues to be of clinical interest. Notably, o-dihydroxycoumarins have been previously shown to be potent iron chelators under neutral conditions. Within this study, the interaction of a series of natural coumarins and their synthetic analogs with copper has been evaluated in order to obtain structure-activity relationships under different pathophysiological pH conditions. Both competitive and non-competitive methods have been employed. Analysis of cupric ion reduction has also been performed. Under mildly competitive conditions, cupric chelation was observed for o-dihydroxycoumarins, and partially for o-diacetoxycoumarin. Non-competitive studies showed that cuprous ions are not chelated at all and that the stoichiometries of the most active 6,7- and 7,8-dihydroxycoumarins to cupric ions ranged from 1:1 to 2:1 depending on pH and concentration. Interestingly, under highly competitive conditions, coumarins were not capable of chelating cupric ions, either. Reduction experiments have shown that 13 out of the 15 coumarins included in this study reduced cupric ions. However, significant differences depending on their structures were apparent in their potencies. O-dihydroxycoumarins were the most potent ones again.

CONCLUSION

O-dihydroxycoumarins are moderately active cupric ion chelators with potent copper reducing properties.

Synthesis and antimycobacterial activity of 1-(β-d-Ribofuranosyl)-4-coumarinyloxymethyl- / -coumarinyl-1,2,3-triazole

A series of β-d-ribofuranosyl coumarinyl-1,2,3-triazoles have been synthesized by Cu-catalyzed cycloaddition reaction between azidosugar and 7-O-/7-alkynylated coumarins in 62-70% overall yields. The in vitro antimycobacterial activity evaluation of the synthesized triazolo-conjugates against Mycobacterium tuberculosis revealed that compounds were bactericidal in nature and some of them were found to be more active than one of the first line antimycobacterial drug ethambutol against sensitive reference strain H37Rv, and 7 to 420 times more active than all four first line antimycobacterial drugs (isoniazid, rifampicin, ethambutol and streptomycin) against multidrug resistant clinical isolate 591. Study of in silico pharmacokinetic profile indicated the drug like characters for the test molecules. Further, transmission electron microscopic experiments revealed that these compounds interfere with the constitution of bacterial cell wall possibly by targeting mycobacterial InhA and DNA gyrase enzymes. Study conducted on the activities of the test compounds on bacterial InhA and DNA gyrase revealed that the most bactericidal test compound, N¹-(β-d-ribofuranosyl)-C⁴-(4-methylcoumarin-7-oxymethyl)-1,2,3-triazole (6b) and its corresponding directly linked conjugate N¹-(β-d-ribofuranosyl)-C⁴-(4-methylcoumarin-7-yl)-1,2,3-triazole (11b) significantly inhibited the activity of both the enzymes. The results were further supported by molecular docking studies of the compound 6b and 11b with bacterial InhA and DNA gyrase B enzymes. Further, the cytotoxicity study of some of the better active compounds on THP-1 macrophage cell line using MTT assay showed that the synthesized compounds were non-cytotoxic.

Enzymatic separation of epimeric 4-C-hydroxymethylated furanosugars: Synthesis of bicyclic nucleosides

Conversion of D-glucose to 4-C-hydroxymethyl-1,2-O-isopropylidene-α-D-ribofuranose, which is a key precursor for the synthesis of different types of bicyclic/spiro nucleosides, led to the formation of an inseparable 1:1 mixture of the desired product and 4-C-hydroxymethyl-1,2-O-isopropylidene-α-D-xylofuranose. A convenient environment friendly Novozyme^®-435 catalyzed selective acetylation methodology has been developed for the separation of an epimeric mixture of ribo- and xylotrihydroxyfuranosides in quantitative yields. The structure of both the monoacetylated epimers, i.e., 5-O-acetyl-4-C-hydroxymethyl-1,2-O-isopropylidene-α-D-ribo- and xylofuranose obtained by enzymatic acetylation, has been confirmed by an X-ray study on their corresponding 4-C-p-toluenesulfonyloxymethyl derivatives. Furthermore, the two separated epimers were used for the convergent synthesis of two different types of bicyclic nucleosides, which confirms their synthetic utility.

Corrigendum to The Competence of 7,8-Diacetoxy-4-Methylcoumarin and Other Polyphenolic Acetates in Mitigating the Oxidative Stress and their Role in Angiogenesis

In the Original Research Article entitled "The Competence of 7, 8-Diacetoxy-4-methylcoumarin and other Polyphenolic Acetates in Mitigating the Oxidative Stress and their Role in Angiogenesis" Published in Current Topics in Medicinal Chemistry, 2015, Vol. 15, No. 2, on page no. 179, the order of author names was rearranged because second authorship is acceptable as they only acknowledge the first and the second authorship as per the new policies of Medical Council of India. The order of authors should be read as follows: Rini Joshi, Vishwajeet Rohil, Shvetambri Arora, Sushma Manral, Ajit Kumar, Sanjay Goel, Nivedita Priya, Prabhjoth Singh, Prija Ponnan, Suvro Chatterji, Bilikere S. Dwarakanath, Daman Saluja, Diwan S. Rawat, Ashok K. Prasad, Luciano Saso, Ekta Kohli, Anthony L. DePass, Marc E. Bracke, Virinder S. Parmar and Hanumantharao G. Raj.

Facile Access to Bromonucleosides Using Sodium Monobromoisocyanurate (SMBI)

Bromonucleosides constitute a significant class of molecules and are well known for their biological activity. 5-Bromouridine, 5-bromo-2'-deoxyuridine, 5-bromouridine-5'-triphosphate, and nucleotides containing 5-bromouridine have been tested and used for numerous biological studies. 8-Bromopurine nucleosides have been used as essential precursors for the synthesis of nucleosides with fluorescent properties. This unit describes protocols for the synthesis of bromonucleosides using sodium monobromoisocyanurate (SMBI) in a straightforward way. Reactions are carried out at room temperature, and aqueous solvent mixtures are used to dissolve the nucleosides. Sodium azide is used as catalyst for the bromination of pyrimidine nucleosides, and no catalyst is necessary for the bromination of purine nucleosides. Unprotected 2'-deoxy pyrimidine and 2'-deoxy purine nucleosides are treated with SMBI to afford C-5 bromo pyrimidine and C-8 bromo purine nucleosides, respectively. This methodology has been found to be efficient for the synthesis of bromonucleosides on gram scale with consistently high yields. © 2017 by John Wiley & Sons, Inc.

Lipase-mediated synthesis of sugar–PEG-based amphiphiles for encapsulation and stabilization of indocyanine green

Bio-catalytically synthesized sugar–PEG-based copolymers form stable micelles in an aqueous medium. These micelles from amphiphilic copolymer are able to efficiently solubilize and stabilize indocyanine green dye (ICG) under physiological conditions.

Synthesis and anti-inflammatory activity evaluation of novel triazolyl-isatin hybrids

New isatin-triazole based hybrids have been synthesized and evaluated for their inhibitory activity of TNF-α induced expression of Intercellular Adhesion Molecule-1 (ICAM-1) on the surface of human endothelial cells. Structure-activity relationship (SAR) studies revealed that the presence of the electron-attracting bromo substituent at position-5 of the isatin moiety played an important role in enhancing the anti-inflammatory potential of the synthesized compounds. Z-1-[3-(1H-1,2,4-Triazol-1-yl)propyl]-5-bromo-3-[2-(4-methoxyphenyl)hydrazono]indolin-2-one (19) with an IC50 = 20 μM and 89% ICAM-1 inhibition with MTD at 200 μM was found to be the most potent of all the synthesized derivatives. Introduction of 1,2,4-triazole ring and electron-donating methoxy group on the phenylhydrazone moiety resulted in four-fold increase of the anti-inflammatory activity.

Design and Synthesis of Triazole-Linked xylo-Nucleoside Dimers

Three triazole-linked nonionic xylo-nucleoside dimers T(L)-t-T(xL), T(L)-t-A(BzxL) and T(L)-t-C(BzxL) have been synthesized for the first time by Cu(I) catalyzed azide-alkyne [3 + 2] cycloaddition reaction (CuAAC) of 1-(3'-azido-3'-deoxy-2'-O,4'-C-methylene-β-D-ribo-furanosyl)thymine with different alkynes, i.e., 1-(5'-deoxy-5'-C-ethynyl-2'-O,4'-C-methylene-β-D-xylofuranosyl)thymine, 9-(5'-deoxy-5'-C-ethynyl-2'-O,4'-C-methylene-β-D-xylo-furanosyl)-N6-benzoyladenine and 1-(5'-deoxy-5'-C-ethynyl-2'-O,4'-C-methylene-β-D-xylofuranosyl)-N4-benzoylcytosine in 90%-92% yields. Among the two Cu(I) reagents, CuSO4.5H2O-sodium ascorbate in THF:(t)BuOH:H2O (1:1:1) and CuBr.SMe2 in THF used for cycloaddition (click) reaction, the former one was found to be better yielding than the latter one.

Synthesis of macromolecular systems via lipase catalyzed biocatalytic reactions: applications and future perspectives

This review highlights the application of lipases in the synthesis of pharmaceutically important small molecules and polymers for diverse applications.