Synthesis of 25-oxygenated D:A-friedooleananes from D:A-friedoolean-7β -ol

D:A-Friedoolean-25-ol ( ) and 25-al ( ) have been synthesised from D:A-friedoolean-7β -ol ( ). Substituted tetrahydrofuran rings are opened up on treatment with lithium in ethylene-diamine to yield the corresponding saturated alcohols.     

Role of cholesterol 10-methyl group and effect of "extra" 14-methyl group on silkworm growth and development

In order to establish the functional importance of the 10-methyl group of cholesterol and the planarity of the steroid ring, silkworms (Bombyx mori) were reared on an artificial diet containing 19-norcholesterol (1), 14 alpha-methylcholesterol (3) or 19,19-difluorocholesterol (2). The former two sterols (1 and 3) only partially satisfied the silkworm sterol requirement; growth and development were seriously retarded. The fluorinated sterol (2) was much more deleterious and was totally inadequate in meeting the sterol requirement.     

Functionalisation of carbon nanohorns

The functionalisation of single wall carbon nanohorns via 1,3-dipolar cycloaddition has been achieved, and the products have been characterised by spectroscopy, microscopy and thermogravimetry.     

Chemical Functionalisation of 2D Materials by Batch and Continuous Hydrothermal Flow Synthesis

2D materials are single or few layered materials consisting of one or several elements with a thickness of a few nanometres. Their unique, tuneable physical and chemical properties including ease of chemical functionalisation makes this class of materials useful in a variety of technological applications. The feasibility of 2D materials strongly depends on better synthetic approaches to improve properties, increase performance, durability and reduce costs. As such, in the synthesis of nanomaterials, hydrothermal processes are widely adopted through a precursor–product synthesis route. This method includes batch or continuous flow systems, both employing water at elevated temperatures (above boiling point) and pressures to fine-tune the physical, chemical, optical and electronic properties of the nanomaterial. Both techniques yield particles with different morphology, size and surface area due to different mechanisms of particle formation. In this Minireview, we present batch and continuous hydrothermal flow synthesis of a selection of 2D derivatives (graphene, MXene and molybdenum disulfide), their chemical functionalisation as an advantageous approach in exploring properties of these materials as well as the benefits and challenges of employing these processes, and an outlook for further research.     

Contributions of the 8-methyl group to the vibrational normal modes of flavin mononucleotide and its 5-methyl semiquinone radical

Resonance Raman spectroscopy is a powerful tool to investigate flavins and flavoproteins, and a good understanding of the flavin vibrational normal modes is essential for the interpretation of the Raman spectra. Isotopic labeling is the most effective tool for the assignment of vibrational normal modes, but such studies have been limited to labeling of rings II and III of the flavin isoalloxazine ring. In this paper, we report the resonance and pre-resonance Raman spectra of flavin mononucleotide (FMN) and its N5-methyl neutral radical semiquinone (5-CH 3FMN(*)), of which the 8-methyl group of ring I has been deuterated. The experiments indicate that the Raman bands in the low-frequency region are the most sensitive to 8-methyl deuteration. Density functional theory (DFT) calculations have been performed on lumiflavin to predict the isotope shifts, which are used to assign the calculated normal modes to the Raman bands of FMN. A first assignment of the low-frequency Raman bands on the basis of isotope shifts is proposed. Partial deuteration of the 8-methyl group reveals that the changes in the Raman spectra do not always occur gradually. These observations are reproduced by the DFT calculations, which provide detailed insight into the underlying modifications of the normal modes that are responsible for the changes in the Raman spectra. Two types of isotopic shift patterns are observed: either the frequency of the normal mode but not its composition changes or the composition of the normal mode changes, which then appears at a new frequency. The DFT calculations also reveal that the effect of H/D-exchange in the 8-methyl group on the composition of the vibrational normal modes is affected by the position of the exchanged hydrogen, i.e., whether it is in or out of the isoalloxazine plane.     

The N6-methyl group of adenine further increases the BI stability of DNA compared to C5-methyl groups

Methylated DNA bases are natural modifications which play an important role in protein-DNA interactions. Recent experimental and theoretical results have shown an influence of the base modification on the conformational behavior of the DNA backbone. MD simulations of four different B-DNA dodecamers (d(GC)(6), d(AT)(6), d(G(5mCG)(5)C), and d(A(T6mA)(5)T)) have been performed with the aim to examine the influence of methyl groups on the B-DNA backbone behavior. An additional control simulation of d(AU)(6) has also been performed to examine the further influence of the C5-methyl group in thymine. Methyl groups in the major groove (as in C5-methylcytosine, thymine, or N6-methyladenine) decrease the BII substate population of RpY steps. Due to methylation a clearer distinction of the BI substate stability between YpR and RpY (CpG/GpC or TpA/ApT) steps arises. A positive correlation between the BII substate population and base stacking distances is seen only for poly(GC). A methyl group added into the major groove increases mean water residence times around the purine N7 atom, which may stabilize the BI substate by improving the hydration network between the DNA backbone and the major groove. The N6-methyl group also forms a water molecule bridge between the N6 and O4 atoms, and thus further stabilizes the BI substate.     

Rotational dynamics of the methyl group in the 4-methyl pyridine crystal

Raman spectra below 150 cm⁻¹ of the 4-methyl pyridine crystal, and its deuterated derivative (d₇), at various temperatures from 276.8 K (melting point) to 5 K are presented and vibrational assignments proposed. Three crystal phases are observed between 5–100 K (III), 100–254 K (II) and 254–276.8 K (I). In phase III, where the site symmetry for the molecule is C₁, different potential shapes are compared and only a non-periodic function accounts satisfactorily for the five τCH₃ and two τCD₃ Raman bands. A molecular model is proposed where the methyl groups are correlated along infinite chains in the crystal.     

Selective substitutions in the C10-methyl group in erythromycin derivatives

A method for chemical modifications of the relatively unreactive C10-methyl group in the erythromycin macrolactone ring has been developed. Erythralosamine was protected as an N-oxide in the N,N-dimethylamino group and reacted with NBS in acetic acid to provide two regioisomeric allylic bromides. The same amine was formed from both isomers on nucleophilic substitution. Both regioisomeric bromides in cross-coupling reactions under Stille conditions provided the same product from substitution in the 10-methyl group via a common π-allylic palladium complex. Under Negishi conditions with trimethylalane, the Pd-catalysed cross-coupling provided the 10-ethyl homologue. X-ray analyses were used to confirm the structure of erythralosamine, and to determine the structures of the allylic bromides from erythralosamine N-oxide.     

Functionalisation of artemisinin and its ring-contracted derivatives

Isoxazoline analogues of artemisinin were obtained in low yield and low diastereoselectivity from the 1,3-dipolar cycloaddition of nitrile oxides. Alternatively, starting from the aldehyde 7, a number of transformations--Wittig reaction and reduction, Henry reaction and cyanohydrin formation--were achieved in significantly higher yields. In the cases where a new stereocenter was introduced this occurred diastereoselectively.     

Reactions of 2, 5-dimethyl-4-triphenylsilylpyridine at the α-methyl group

5-Methyl-4-triphenylsilylpyridine-2-carboxylic acid was synthesized, esterified, and decarboxylated. Several transformations of trans-5-methyl-4-triphenylsilyl-2-styrylpyridine were examined.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 957–961, July, 1972.     

Functionalisation of heteroaromatic N-oxides using organic superbase catalyst

Functionalisation of quinoline N-oxide was investigated using phophazene base as a catalyst; alkynylation and heteroarylation at 2-position were successfully achieved via nucleophilic addition-elimination process.     

Chemical Functionalisation and Photoluminescence of Graphene Quantum Dots

Chemical modification of graphene quantum dots (GQDs) can influence their physical and chemical properties; hence, the investigation of the effect of organic functional groups on GQDs is of importance for developing GQD–organic hybrid materials. Three peripherally functionalised GQDs having a third‐generation dendritic wedge (GQD‐ 2 ), long alkyl chains (GQD‐ 3 ) and a polyhedral oligomeric silsesquioxane group (GQD‐ 4 ) were prepared by the Cu^I‐catalysed Huisgen cycloaddition reaction of GQD‐ 1 with organic azides. Cyclic voltammetry indicated that reduction occurred on the surfaces of GQD‐ 1 – 4 and on the five‐membered imide rings at the periphery, and this suggested that the functional groups distort the periphery by steric interactions between neighbouring functional groups. The HOMO–LUMO bandgaps of GQD‐ 1 – 4 were estimated to be approximately 2 eV, and their low‐lying LUMO levels (<?3.9 eV) were lower than that of phenyl‐C₆₁‐butyric acid methyl ester, an n‐type organic semiconductor. The solubility of GQD‐ 1 – 4 in organic solvents depends on the functional groups present. The functional groups likely cover the surfaces and periphery of the GQDs, and thus increase their affinity for solvent and avoid precipitation. Similar to GQD‐ 2 , both GQD‐ 3 and GQD‐ 4 emitted white light upon excitation at 360 nm. Size‐exclusion chromatography demonstrated that white‐light emission originates from the coexistence of differently sized GQDs that have different photoluminescence emission wavelengths.     

Functionalisation of unactivated methyl groups through cyclopalladation reactions

The transformation of the organopalladium compound (3) into the corresponding deuteriated, chlorinated, or oxidized derivatives (7), (8), or (9), (11), and (12) respectively. is described. The palladation of compound (9) takes place regioselectively leading to the palladated system (13), which is transformed into the difunctionalised oximes (15) and (16). The palladation of $\text{E}$-2,2-dimethyl and 2,2,6,6-tetramethyl-cyclohexanone oxime leads to the corresponding organopalladium compounds (17) and (27), which through deuteriation or oxidation affords the expected products (21) and (31), or (22), (23), (24), and (32), respectively. The second palladation of the compound (22) takes place on the remaining methyl group yielding the organopalladium derivative (26). Finally, $\text{E}$-lupanone oxime is palladated selectively in the 23-position leading to the organopalladium compound (38); the transformation of this compound into its 23-deuterio and 23-acetoxy- derivatives (41) and (42), respectively is also described. The stereochemistry in the palladatlon of lupanone oxime is deduced from NOE studies at 500 MHz.     

Orthogonal Functionalisation of Upconverting NaYF4 Nanocrystals

A simple and straightforward method for the orthogonal functionalisation of upconverting NaYF₄ nanocrystals (UCNCs)—doped withYb³⁺ and Er³⁺—based on N‐(3‐dimethylaminopropyl)‐N′‐ethylcarbodiimide/N‐hydroxysuccinimide (EDC/NHS) selective reactions between two dyes and two different reactive groups present at the periphery of the upconverting nanocrystals is reported. Organic‐soluble UCNCs of 10 and 50 nm in size are encapsulated efficiently in a 1:1 mixture of two commercial 3000 Da poly(ethylene glycol) derivatives with two different reactive groups (amino and carboxylic groups). The water‐dispersible UCNCs are non‐cytotoxic, stable in the physiological environment, and present free amine and carboxylic reactive groups on their periphery, allowing rapid, selective, and modular covalent conjugation to payloads through EDC/NHS reactions. PEG‐encapsulated UCNCs with and without covalent conjugation to payloads are characterised in vitro through spectroscopic, dynamic light scattering, and electron microscopy measurements. Living cell analyses coupled with TEM measurements confirm the uptake and low cytotoxicity of the coated UCNCs. They are linked covalently to two different dyes, internalised by living cells, and analysed by confocal microscopy. The related colocalisation measurements prove the reactivity of both amines and carboxylic acids on the periphery of the nanocrystals. This approach demonstrates that it is possible to produce water‐dispersible and cyto‐compatible dual‐functional UCNCs.     

Methods for the Functionalisation of Nanoparticles: New Insights and Perspectives

In the field of nanometre‐sized drug‐delivery systems, a wide range of colloidal systems have been created in recent decades. All of the systems have a similar global structure, that is, an inner part and an external surface/interface. In several applications, the external interface is the support for desired properties and the basis of future developments. The engineering of the particle’s surface is an emerging step in the design of systems at the nanometre scale. This review presents and summarises the available techniques with a particular attention to recent advances. It is also a base for future works in this expanding area of research.     

Late-Stage Functionalisation of Pyridine-Containing Bioactive Molecules: Recent Strategies and Perspectives

Late-Stage Functionalisation (LSF) is an innovative technique that has been successfully applied to the C−H diversification of pharmaceuticals. However, LSF of the pyridine ring in drug-like molecules is often unselective. As a result, a mixture of structurally related products is obtained, thus making the purification tedious and time-consuming. This review shines a light on recent strategies addressing the selectivity issue in the LSF of complex natural products or drugs containing the pyridine moiety. Specifically, we have reviewed the efforts reported both in academia and industries with the hope of providing a guide for the LSF of elaborated pyridines.