A General Strategy for the Synthesis of Rare Sugars via Ru(II)-catalyzed and Boron-mediated Selective Epimerization of 1,2-trans-diols to 1,2-cis-diols

Human glycans are primarily composed of nine common sugar building blocks. On the other hand, several hundred monosaccharides have been discovered in bacteria and most of them are not readily available. The ability to access these rare sugars and the corresponding glycocon-jugates can facilitate the studies of various fundamentally important biological processes in bacteria, including interactions between microbiota and the human host. Many rare sugars also exist in a variety of natural products and pharmaceutical reagents with significant biological activi-ties. Although methods have been developed for the synthesis of rare monosaccharides, most of them involve lengthy steps. Herein we report an efficient and general strategy that can provide access to rare sugars from commercially available common monosaccharides via a one-step Ru(II)-catalyzed and boron-mediated selective epimerization of 1,2-trans-diols to 1,2-cis-diols. The formation of boronate esters drives the equilibrium towards 1,2-cis-diol products, which can be immediately used for further selective functionalization and glycosylation. The utility of this strategy was demonstrated by the efficient construction of glycoside skeletons in natural products or bioactive compounds.

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Direct Cyclization of Alkenyl Thioester via Transition Metal‐hydrogen Atom Transfer/radical‐polar Crossover Mechanism

10.26434/chemrxiv.10247813.v1 ◽

2019 ◽

Author(s):

Shiori Date ◽

Kensei Hamasaki ◽

Karen Sunagawa ◽

Hiroki Koyama ◽

Chikayoshi Sebe ◽

...

Keyword(s):

Natural Products ◽

Hydrogen Atom ◽

Transition Metal ◽

Hydrogen Atom Transfer ◽

Synthetic Method ◽

Atom Transfer ◽

Reaction Conditions ◽

Hydride Hydrogen ◽

Sulfur Heterocycles ◽

One Step

<div>We report here a catalytic, Markovnikov selective, and scalable synthetic method for the synthesis of saturated sulfur heterocycles, which are found in the structures of pharmaceuticals and natural products, in one step from an alkenyl thioester. Unlike a potentially labile alkenyl thiol, an alkenyl thioester is stable and easy to prepare. The powerful Co catalysis via a cobalt hydride hydrogen atom transfer and radical-polar crossover mechanism enabled simultaneous cyclization and deprotection. The substrate scope was expanded by the extensive optimization of the reaction conditions and tuning of the thioester unit.</div>

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Selective Functionalization at N2-Position of Guanine in Oligonucleotides via Reductive Amination

10.26434/chemrxiv.12511661.v1 ◽

2020 ◽

Author(s):

Bapurao Bhoge ◽

Ishu Saraogi

Keyword(s):

Organic Chemistry ◽

Chemical Biology ◽

Reductive Amination ◽

The Other ◽

Dna Oligomers ◽

Site Specific ◽

Wide Applicability ◽

Dna Oligonucleotides ◽

Selective Functionalization

Chemo- and site-specific modifications in oligonucleotides have wide applicability as mechanistic probes in chemical biology. Here we have employed a classical reaction in organic chemistry, reductive amination, to selectively functionalize the N<sup>2</sup>-amine of guanine/2’-deoxyguanine monophosphate. This method specifically modifies guanine in several tested DNA oligonucleotides, while leaving the other bases unaffected. Using this approach, we have successfully incorporated desired handles chemoselectively into DNA oligomers.

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Chiral Sulfoxides as Building Blocks for Enantiopure 1,3-Diol Precursors in the Synthesis of Natural Products

Current Organic Synthesis ◽

10.2174/157017941006140206103254 ◽

2014 ◽

Vol 10 (6) ◽

pp. 885-902 ◽

Cited By ~ 8

Author(s):

Claude Bauder ◽

Jean Martínez ◽

Xavier Salom-Roig

Keyword(s):

Natural Products ◽

Building Blocks ◽

Chiral Sulfoxides

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Formation of Carbon-Oxygen Bond Mediated by Hypervalent Iodine Reagents Under Metal-free Conditions

Mini-Reviews in Organic Chemistry ◽

10.2174/1570193x17999200807140943 ◽

2020 ◽

Vol 17 ◽

Author(s):

Ayesha Jalil ◽

Yaxin O Yang ◽

Zhendong Chen ◽

Rongxuan Jia ◽

Tianhao Bi ◽

...

Keyword(s):

Natural Products ◽

Bond Formation ◽

Building Blocks ◽

Review Article ◽

Hypervalent Iodine ◽

Metal Free ◽

Bioactive Natural Products ◽

The Past ◽

Oxygen Bond ◽

Privileged Scaffolds

: Hypervalent iodine reagents are a class of non-metallic oxidants have been widely used in the construction of several sorts of bond formations. This surging interest in hypervalent iodine reagents is essentially due to their very useful oxidizing properties, combined with their benign environmental character and commercial availability from the past few decades ago. Furthermore, these hypervalent iodine reagents have been used in the construction of many significant building blocks and privileged scaffolds of bioactive natural products. The purpose of writing this review article is to explore all the transformations in which carbon-oxygen bond formation occurred by using hypervalent iodine reagents under metal-free conditions

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Improvement of Gain Accuracy and CMRR of Low Power Instrumentation Amplifier Using High Gain Operational Amplifiers

Micro and Nanosystems ◽

10.2174/1876402912666200123153318 ◽

2020 ◽

Vol 12 (3) ◽

pp. 168-174

Author(s):

Rashmi Sahu ◽

Maitraiyee Konar ◽

Sudip Kundu

Keyword(s):

Low Power ◽

Building Blocks ◽

High Gain ◽

The Other ◽

Operational Amplifiers ◽

Instrumentation Amplifier ◽

Biomedical Signals ◽

Op Amp ◽

Op Amps ◽

Multi Stage

Background: Sensing of biomedical signals is crucial for monitoring of various health conditions. These signals have a very low amplitude (in μV) and a small frequency range (<500 Hz). In the presence of various common-mode interferences, biomedical signals are difficult to detect. Instrumentation amplifiers (INAs) are usually preferred to detect these signals due to their high commonmode rejection ratio (CMRR). Gain accuracy and CMRR are two important parameters associated with any INA. This article, therefore, focuses on the improvement of the gain accuracy and CMRR of a low power INA topology. Objective: The objective of this article is to achieve high gain accuracy and CMRR of low power INA by having high gain operational amplifiers (Op-Amps), which are the building blocks of the INAs. Methods: For the implementation of the Op-Amps and the INAs, the Cadence Virtuoso tool was used. All the designs and implementation were realized in 0.18 μm CMOS technology. Results: Three different Op-Amp topologies namely single-stage differential Op-Amp, folded cascode Op-Amp, and multi-stage Op-Amp were implemented. Using these Op-Amp topologies separately, three Op-Amp-based INAs were realized and compared. The INA designed using the high gain multistage Op-Amp topology of low-frequency gain of 123.89 dB achieves a CMRR of 164.1 dB, with the INA’s gain accuracy as good as 99%, which is the best when compared to the other two INAs realized using the other two Op-Amp topologies implemented. Conclusion: Using very high gain Op-Amps as the building blocks of the INA improves the gain accuracy of the INA and enhances the CMRR of the INA. The three Op-Amp-based INA designed with the multi-stage Op-Amps shows state-of-the-art characteristics as its gain accuracy is 99% and CMRR is as high as 164.1 dB. The power consumed by this INA is 29.25 μW by operating on a power supply of ±0.9V. This makes this INA highly suitable for low power measurement applications.

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One-step Separation and Purification of Four Phenolic Acids from Stenoloma chusanum (L.) Ching by Medium-pressure Liquid Chromatography and High-speed Counter-current Chromatography

The Natural Products Journal ◽

10.2174/2210315508666181004115422 ◽

2019 ◽

Vol 9 (2) ◽

pp. 138-143

Author(s):

Tianyun Li ◽

Xiling Dai ◽

Yichen Li ◽

Guozheng Huang ◽

Jianguo Cao

Keyword(s):

Natural Products ◽

Liquid Chromatography ◽

Phenolic Acids ◽

High Speed ◽

High Efficiency ◽

Total Phenolic ◽

Medium Pressure ◽

Medium Pressure Liquid Chromatography ◽

One Step ◽

Counter Current

Background:Stenoloma chusanum (L.) Ching is a Chinese traditional medicinal fern with high total flavonoid and total phenolic content. Traditionally, phenolic compounds were separated by using column chromatography, which is relatively inefficient. </P><P> Objective: This study aims to use an efficient method to separate natural products from S. chusanum by Medium-Pressure Liquid Chromatography (MPLC) and High-Speed Counter-Current Chromatography (HSCCC).Methods:In the present research, firstly, a sample (2.5 g) from the dichloromethane extract of S. chusanum was separated by MPLC. Next, fraction P5 was purified by HSCCC with a two-phase solvent system composed of hexane-ethyl acetate-methanol-water (HEMWat) at a volume ratio of 2:4:1:4 (v/v/v/v). </P><P> Result: Four phenolic acids were obtained and their structures were identified by means of NMR and ESI-mass analysis. They were identified as: 1) protocatechuic acid (34 mg, purity 90.1%), 2) syringic acid (66 mg, purity 99.0%), 3) p-hydroxybenzoic acid (5 mg, purity 91.2%) and 4) vanillic acid (6 mg, purity 99.3%).Conclusion:The combination of MPLC and HSCCC is a high-efficiency separation method for natural products. This is the first report with regard to the separation of four phenolic acids in one step by MPLC and HSCCC from S. chusanum (L.) Ching.

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Interrelationship of Jatharagni and Dhatvagni in context to Dhatvagni Pradoshaj Vikaras.

Journal of Ayurveda and Integrated Medical Sciences (JAIMS) ◽

10.21760/jaims.v2i1.7508 ◽

2017 ◽

Vol 2 (1) ◽

Author(s):

Kishor G. Satani ◽

Hemang Raghvani ◽

Kunjal Bhatt

Keyword(s):

Basic Concept ◽

Functional Relationship ◽

Structural Relationship ◽

The Other ◽

Proper Function ◽

One Step ◽

Material Form

The concept of Agni is basic concept of Ayurveda. Agni is believed to be the agency for any kind of transformation. Maharshi Vagbhatta says that each of the Dosha, Dhatu, Mala etc. have their own Agni. This is how the number of Agni cannot be limited. Though each and every Agni has its own importance, Dehagni or Jatharagni is the most important one as all other Agnis are depended upon Dehagni. Acharya Vagbhatta says that proper function of every Dhatvagni is depended on the Jatharagni. Increase or decrease of Jatharagni directly affects the function of Dhatvagni. Thus, Maharshi Charaka established functional relationship among Jatharagni and other Agnis. Maharshi Vagbhattta goes one step ahead of Maharshi Charaka by using word “Amsha” means; moieties of Kayagni, located to in its own place, are distributed to and permeate to all the Dhatus. A decrease of it (below the normal) makes for an increase of the Dhatus, while an increase of it (above the normal) makes for a decrease of a Dhatus. This shows structural relationship too, between Jatharagni and Dhatvagni as “Amsha” always indicates Murtatva or material form. Further more all these Agnis are connected with each other and due to this relationship, vitiation of Jatharagni results in vitiation of all the other Agnis.

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Synthesis of Polycycles and Oxacycles by Tandem Metathesis of endo–norbornene Derivatives

Synthesis ◽

10.1055/a-1348-4242 ◽

2021 ◽

Author(s):

Sambasivarao Kotha ◽

Sunil Pulletikurti ◽

Ambareen Fatma ◽

gopal dhangar ◽

gonna somu Naidu

Keyword(s):

Natural Products ◽

Metal Complex ◽

Carbonyl Group ◽

Single Step ◽

Time Dependent ◽

Computational Studies ◽

Nmr Studies ◽

Tricyclic Compounds ◽

One Step ◽

Norbornene Derivatives

Here, we have demonstrated that the presence of a carbonyl group at C7 position is preventing the olefin metathesis of endo-norbornene derivatives due to the complexation of the metal alkylidene. Time-dependent NMR studies showed the presence of new proton signals in the metal alkylidene region, which indicate the formation of metal complex with the carbonyl group of the substrate. These observations were further proved by ESI-MS analysis. Whereas, computational studies provided that the catalyst was interacting with the C7 carbonyl group and aligned perpendicular to that of norbornene olefin. Later, these endo-keto norbornene derivatives were reduced to hydroxyl derivatives diastereoselectively. Ring-rearrangement metathesis (RRM) of these hydroxyl derivatives, produced the [6/5/6], and [5/6/5] carbo-tricyclic cores of the natural products in one step. Whereas the RRM of O-allyl derivatives, delivered the oxa-tricyclic compounds in a single step with excellent yields.

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Non-Enzymatic Desymmetrization Reactions in Aqueous Media

Symmetry ◽

10.3390/sym13040720 ◽

2021 ◽

Vol 13 (4) ◽

pp. 720

Author(s):

Satomi Niwayama

Keyword(s):

Natural Products ◽

Total Synthesis ◽

Functional Groups ◽

Organic Compounds ◽

Recent Progress ◽

Aqueous Media ◽

Building Blocks ◽

Organic Reactions ◽

Environmentally Benign ◽

Enzymatic Desymmetrization

Symmetric organic compounds are generally obtained inexpensively, and therefore they can be attractive building blocks for the total synthesis of various pharmaceuticals and natural products. The drawback is that discriminating the identical functional groups in the symmetric compounds is difficult. Water is the most environmentally benign and inexpensive solvent. However, successful organic reactions in water are rather limited due to the hydrophobicity of organic compounds in general. Therefore, desymmetrization reactions in aqueous media are expected to offer versatile strategies for the synthesis of a variety of significant organic compounds. This review focuses on the recent progress of desymmetrization reactions of symmetric organic compounds in aqueous media without utilizing enzymes.

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