N,N-Diacylaminals as Emerging Tools in Synthesis: From Peptidomimetics to Asymmetric Catalysis

N,N-Diacylaminals are flexible molecular scaffolds that have commonly been utilized as amide surrogates in peptidomimetics. The singularities of this motif as an N-acyl imine equivalent and as hydrogen-bond donor have recently opened new synthetic opportunities, especially in the field of asymmetric catalysis. This concept article highlights this diverse synthetic potential and provides the elements necessary for further developments.     

Green chemistry in United States science policy

ABSTRACT

Although optimizing each of the Twelve Principles of Green Chemistry is necessary for achieving the greenest possible chemistry in the lab, there are additional creative ways to promote green chemistry not encompassed by these. Communicating to society the importance of green chemistry beyond the laboratory is essential. Of course, doing this effectively presents distinct challenges to those encountered when designing chemical syntheses. Here, I discuss several observations from my time working in federal science policy as an American Association for the Advancement of Science/American Chemical Society Congressional Science Fellow in the United States Senate. I suggest a practical science policy exercise that could be included as a companion to learning in the laboratory or classroom. This assignment provides an avenue to address broader applications of science to society while exposing students to meaningful ways to be involved in the democratic process beyond voting.     

“Green Star”: a holistic Green Chemistry metric for evaluation of teaching laboratory experiments

Abstract

This paper presents a new semi-quantitative metric, Green Star (GS), for evaluation of the global greenness of chemical reactions used in teaching laboratories. Its purpose is to help choose the more acceptable reactions for implementing Green Chemistry (GC) and to identify suitable modifications of protocols to improve the greenness of the chemistry practiced by students. GS considers globally, in principle, all the Twelve Principles of GC. The metric consists in the evaluation of the greenness of the reaction for each principle by pre-defined criteria, followed by graphical representation of the results in an Excel radar chart – the fuller the chart, the higher degree of greenness. To illustrate the construction and the scope of the metric, a case study is presented – the iron(II) oxalate dihydrate synthesis performed under several sets of conditions to pursue the implementation of greenness.     

Perimidine-based synthetic receptors for determination of copper(II) in water solution

Perimidine-based chelators 1 and 2 were prepared, and their structures were confirmed by ¹H and ¹³C NMR, MS spectroscopy and elemental analysis. These compounds were studied as specific synthetic receptors for the recognition of transition metal ions. They exhibited high affinity and selectivity towards Cu(II) ions. The conditional binding constants, linear dynamic range and detection limit were determined by UV–vis spectroscopy. These parameters demonstrated high potential of the prepared synthetic receptors for the recognition and determination of Cu(II) ions. The minimum detectable concentrations of Cu(II) ions for the synthetic receptors 1 and 2 were 270 and 75 nM (R ² = 0.9915 and 0.9964) in aqueous medium (water/DMSO; 99:1 (v/v)), respectively.     

1-Alkynyl Disulfides and their 1-Thiapropargyl-3-Thiaallenyl Rearrangements

Abstract

Twelve new 1-alkynyl disulfides,¹ R¹-C≡C-S-S-R², 1, for the first time including aromatic examples, have been prepared according eqns. (1/2) and/or (3) and characterized.     

A New Synthesis of 3-Deoxy-D-Manno-Octulosonic Acid (KDO) From D-Mannose Via Condensation of Dioxene

Abstract

The title compound has long been known as an essential component of lipopolysaccharides (LPS) and capsular polysaccharides which exist in the outer membrane of Gram-negative bacteria. KDO has attracted additional attention as a consequence of some remarkable discoveries; i) mutants unable to produce KDO are non-viable.¹ ii) KDO is not present in mammalian cells,² iii) the 2-deoxy analog of β-KDO represents a new class of synthetic antimicrobial agent.^3,4 Although syntheses of KDO have been reported by many groups,^5–8 a more efficient synthetic method endowed with the potential for synthesis of not only complex glycoconjugates but also biologically significant analogs is required.     

Synthetic approaches toward piperidine related structures: A review

Abstract

The current review covers explosive development of various synthetic approaches for piperidine scaffold and its analogues in the last few decades. The piperidine ring system is a key motif in many natural alkaloids and synthetic organic compounds. Further, piperidine moiety has gained significant consideration in drug discovery due to its wide range of therapeutic applications.     

Self-Assembling Synthetic Oligopeptide-Based Gelators

Synthetic self-assembling oligopeptide gelators are an important class of compounds which form thermoreversible gels in various organic solvents as well as in aqueous medium. These gels are soft, viscoelastic materials which are envisaged for useful applications in biological and material sciences. The terminally protected self-assembling synthetic tripeptide Boc-Ala-Aib-β-Ala-OMe 1 (Aib: α-aminoisobutyric acid i.e. dimethyl glycine and β-Ala: β-Alanine) forms gels in various organic solvents, whereas its structural analog i.e. the peptide Boc-Ala-Gly-β-Ala-OMe 2 (another self-assembling synthetic tripeptide) fails to form gels under similar conditions and this issue has been addressed. The terminally protected tripeptide Boc-Ala-Val-Ala-OMe 3 has been found to form gels in different aromatic organic solvents. Several structural analogs of peptide 3 [using small structural changes either in protecting groups (at the N or C-terminal position) or in amino acid side chains] have been synthesized, characterized and studied for gelation to address the question how structural changes can regulate the gelation property. Results of the gelation studies indicate that some structural changes are useful to make new peptide gelators with some variations in gelation property and efficiency, while a few structural changes in the protecting groups are really detrimental, leading to abolition the gelation property. These gels are studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier-Transform Infrared (FT-IR) spectroscopy and ¹H NMR studies.     

Identification of Mixtures of Synthetic Organic Pigments Using UV-VIS Spectrophotometry and Kalman Filtering

Abstract

A Kalman filter is used to determine the number of components and their concentrations in mixtures of synthetic organic pigments. In this way, a quantitative identification of mixtures of these pigments is possible as is shown with a simulated as well a real mixture. The dataset used in the experiments, consisted of as much as 27 candidate pigments.     

Towards More Efficient,Greener Syntheses through Flow Chemistry

Technological advances have an important role in the design of greener synthetic processes. In this Personal Account, we describe a wide range of thermal, photochemical, catalytic, and biphasic chemical transformations examined by our group. Each of these demonstrate how the merits of a continuous flow synthesis platform can align with some of the goals put forth by the Twelve Principles of Green Chemistry. In particular, we illustrate the potential for improved reaction efficiency in terms of atom economy, product yield and reaction rates, the ability to design synthetic process with chemical and solvent waste reduction in mind as well as highlight the benefits of the real‐time monitoring capabilities in flow for highly controlled synthetic output.     

Solvent-free reactivity in the undergraduate organic laboratory

Abstract

This review highlights progress made since 2000 in the development of solvent-free organic reactions for student use. It is directed at university instructors to illustrate the broad scope of solventless reactivity possible in undergraduate laboratories. Eliminating a reaction medium directly addresses the Twelve Principles of Green Chemistry and is a focal point of contemporary industrial research. Experimental conditions are straightforward to implement and include reactant grinding, room temperature stirring, microwave irradiation, and conventional heating. A wide range of functional group transformations is easily achievable. Solvent-free reactions are often complete in a matter of minutes and routinely require simplistic work-up and purification protocols. Procedures are compiled from educational resources (primarily pedagogical journals and laboratory manuals) and corollary green experimental elements emphasized where possible.     

A Conveniant Preparation of γ-Formylalkanephosphonates

Abstract

Despite their obvious potential as synthetic intermediate, relatively little attention has been directed to the preparation of γ-formylalkane phosphonates. Because of our interest in the possible utilisation of these compounds as starting materials for the preparation of aminophosphonic acids a new approach has been devised.     

S-2-甲氧基环己酮的合成研究

优化了S-2-甲氧基环己酮的合成方法, 该合成路线产率高、成本低、适合于生产; 并利用S-2-甲氧基环己酮合成了用于制备新一类β-内酰胺类抗生素sanfetrinem cilexetil 的关键中间体2.     

<Emphasis Type="Italic">N</Emphasis>-Alkoxy-3,5-dinitro-4-aminobenzoic acid derivatives with controlled physico-chemical properties

Starting from 4-chloro-3,5-dinitrobenzoic acid 1, compounds 2–10 (N-alkoxy-3,5-dinitro-4-aminobenzoic acid esters where alkoxy stands for methoxy, carboxymethoxy, triphenylmethoxy, or corresponding amides) have been obtained, from which compounds 3–5 and 7–10 are new, and for the known compounds 2 and 6 the synthetic procedure has been improved. The new derivatives have been characterized by appropriate means (IR, UV–Vis, ¹H- and ¹³C-NMR, fluorescence) and their properties were studied. Thus, depending on their structure, the compounds have acid properties, fluorescence and complexing properties with alkaline cations.     

Ring–Opening of a Carbohydrate Triflate to form an Acyclic Alkene

ABSTRACT

The ease with which carbohydrate trifluoromethanesulfonates (triflates) undergo substitution reactions with a wide variety of nucleophiles¹ has allowed these compounds to play an increasingly important role in synthetic carbohydrate chemistry.² The exceptional reactivity of triflates also creates an opportunity for unusual reactions to occur;³ for example, triflyl group migration⁴ and internal displacement by very weak nucleophiles⁵ both have been observed. Also, carbohydrate triflates have been used as alkylating agents in oligosaccharide synthesis.⁶ In this communication a new triflate reaction is described. This new process is one in which departure of the triflyloxy group is accompanied by ring opening to give an acyclic alkene.     

Naphthochromenones: Organic Bimodal Photocatalysts Engaging in Both Oxidative and Reductive Quenching Processes

Twelve naphthochromenone photocatalysts (PCs) were synthesized on gram scale. They absorb across the UV/Vis range and feature an extremely wide redox window (up to 3.22 eV) that is accessible using simple visible light irradiation sources (CFL or LED). Their excited‐state redox potentials, PC*/PC^.? (up to 1.65 V) and PC^.+/PC* (up to ?1.77 V vs. SCE), are such that these novel PCs can engage in both oxidative and reductive quenching mechanisms with strong thermodynamic requirements. The potential of these bimodal PCs was benchmarked in synthetically relevant photocatalytic processes with extreme thermodynamic requirements. Their ability to efficiently catalyze mechanistically opposite oxidative/reductive photoreactions is a unique feature of these organic photocatalysts, thus representing a decisive advance towards generality, sustainability, and cost efficiency in photocatalysis.     

Synthesis of (±)-Bimatoprost

A general synthetic approach has been developed for the synthesis of a key intermediate (6) that can be elaborated into several ophthalmic prostaglandins and their derivatives. Using these strategy, we have obtained (±)-bimatoprost (1) and its analog, (±)-homobimatoprost (5).