Search Results (13)

The calcium-sensing receptor (CaSR) is a validated therapeutic target in the treatment of hyperparathyroidism and related diseases. The CaSR ago-positive allosteric modulator (PAM), AC265347 (1), exhibits a chemically and pharmacologically unique profile compared to current approved CaSR PAM therapeutics. Herein, we report a series of ‘next-generation’ analogues of AC265347, investigating the impact of structural modifications at the stereogenic centre on CaSR PAM activity. Compounds 5 and 7b featuring the alcohol functional group showed ago-PAM profiles comparable to 1, whilst compounds 6, 7 and 9 devoid of this functionality were ‘pure’ PAMs with no intrinsic agonism. These novel chemical tools provide an opportunity to explore the therapeutic potential of AC265347-like PAMs as a function of affinity, cooperativity and intrinsic agonism. Full article

1,4- and 1,2-additons of secondary phosphine oxides to (1R)-myrtenal and (1S)-myrtanal were evaluated as potential routes to P,C-stereogenic phosphine oxides bearing additional hydroxyl or aldehyde functions. 1,4-Additions of racemic secondary phosphine oxides to (1R)-myrtenal were found to offer moderate to good stereoselectivity which shows some promise for utility in kinetic resolution processes, especially at lower conversions. In case of 1,2-additions making the process doubly asymmetric by using an enantiomerically pure secondary phosphine oxide as substrate turned out to be practical. The stereochemical course of the addition reactions under study is presented. The P-resolved 1,2-addition products were demonstrated to undergo facile reduction by BH₃ at room temperature leading to the formation of the corresponding α-hydroxyphosphine-boranes with clean inversion of configuration at the P-centre. All P,C-stereogenic phosphine oxides and boranes that were isolated in the form of a single diastereoisomer were assigned their absolute configurations by means of X-ray crystallography and/or 2D NMR spectral techniques. Full article

PF74 is a capsid-targeting inhibitor of HIV replication that effectively perturbs the highly sensitive viral uncoating process. A lack of information regarding the optical purity (enantiomeric excess) of the single stereogenic centre of PF74 has resulted in ambiguity as to the potency of different samples of this compound. Herein is described the synthesis of enantiomerically enriched (S)- and (R)-PF74 and further enrichment of the samples (≥98%) using chiral HPLC resolution. The biological activities of each enantiomer were then evaluated, which determined (S)-PF74 (IC₅₀ 1.5 µM) to be significantly more active than (R)-PF74 (IC₅₀ 19 µM). Computational docking studies were then conducted to rationalise this large discrepancy in activity, which indicated different binding conformations for each enantiomer. The binding energy of the conformation adopted by the more active (S)-PF74 (ΔG = −73.8 kcal/mol) was calculated to be more favourable than the conformation adopted by the less active (R)-enantiomer (ΔG = −55.8 kcal/mol) in agreement with experimental observations. Full article

Optically active (−)₅₈₉ethyl (S)-2-phenylbutyl thioether, (−)(S)_C-Et(PhBu)S (I), and its new diastereoisomeric mercury (II) chloride adduct, 1:2, (−)[(S)_S(S)_C-Et(PhBu)S.(HgCl₂)₂]₂, (II) were stereoselectively synthesized; the absorbance (UV) and circular dichroism (CD) spectra were measured and the crystal and molecular structure of complex (II) was determined by single-crystal X-ray diffraction. Two different Hg centres are present whose coordination environments are built by two short bonds to chloride ligands in one case, and to one chloride and one sulphur in the other one. These originate digonal units. Electroneutrality is achieved by a further chlorine, which can be considered prevalently ionic and bonded to the two Hg centres, forming square bridging systems nearly perpendicular to the digonal molecules. The coordination polyhedra can be interpreted as 2 + 4 tetragonally-compressed octahedra with the four longer contacts lying in the equatorial plane. IR spectroscopic data are consistent with the presence of one bent and one linear Cl–Hg–Cl moiety. The absolute configurations at both stereogenic centres of the formed diastereoisomeric complex (II) are (S). The (S)_S absolute configuration at the stereogenic sulphur atom bonded to the mercury(II) atom in complex (II) has been related with the negative Cotton effect assigned in its circular dichroism (CD) spectrum to a charge-transfer transition at ca. 230 nm. The stereoselective oxidation of (I) and (II) with hydrogen peroxide, induced by the stereogenic carbon atom (S)_C of the enantiopure sulphide, gave (−)₅₉₈ethyl (S)_C-2-phenylbutyl(S)_S-sulphoxide, (−)₅₉₈[(S)_S(S)_C-Et(PhBu)SO], (III), having 18.1% de. Oxidations carried out in the presence of a 200 molar excess of mercury(II) chloride gave (−)₅₉₈ethyl (S)_C-2-phenylbutyl(R)_S-sulphoxide, (−) ₅₉₈[(R)_S(S)_C-Et(PhBu)SO], (IV) with 31% de, showing the cooperative influence of mercury(II) chloride on the selectivity of the oxidation reaction. Full article

By means of copper(I)-and ruthenium(II)-catalyzed click reactions of quinine- and quinidine-derived alkynes with azide-substituted chalcones a systematic series of novel cinchona-chalcone hybrid compounds, containing 1,4-disubstituted- and 1,5-disubstituted 1,2,3-triazole linkers, were synthesized and evaluated for their cytotoxic activity on four human malignant cell lines (PANC-1, COLO-205, A2058 and EBC-1). In most cases, the cyclization reactions were accompanied by the transition-metal-catalyzed epimerization of the C9-stereogenic centre in the cinchona fragment. The results of the in vitro assays disclosed that all the prepared hybrids exhibit marked cytotoxicity in concentrations of low micromolar range, while the C9-epimerized model comprising quinidine- and (E)-1-(4-(3-oxo-3-(3,4,5-trimethoxyphenyl)prop-1-en-1-yl)phenyl) fragments, connected by 1,5-disubstituted 1,2,3-triazole linker, and can be regarded as the most potent lead of which activity is probably associated with a limited conformational space allowing for the adoption of a relatively rigid well-defined conformation identified by DFT modelling. The mechanism of action of this hybrid along with that of a model with markedly decreased activity were approached by comparative cell-cycle analyses in PANC-1 cells. These studies disclosed that the hybrid of enhanced antiproliferative activity exerts significantly more extensive inhibitory effects in subG1, S and G2/M phases than does the less cytotoxic counterpart. Full article

A new and direct approach to the construction of the core framework of the herbicidal natural products cornexistin and hydroxycornexistin has been developed. Formation of the nine-membered carbocycle found in the natural products has been accomplished by an intramolecular Nozaki-Hiyama-Kishi reaction between a vinylic iodide and an aldehyde. Good yields of carbocyclic products were obtained from the reaction, but diastereomeric mixtures of allylic alcohols were produced. The cyclisation reaction was successful irrespective of the relative configuration of the stereogenic centres in the cyclisation precursor. Full article

The first total synthesis of carmabin A and dragomabin was achieved at 52.3 mg and 43.8 mg scale, respectively. The synthesis led to determination of the configuration of carmabin A and reassignment of the configuration of dragomabin at the stereogenic centre on the alkyne-bearing fragment. Full article

α’-1’-Hydroxyethyl-γ-butyrolactone—a product of reduction of α-acetylbutyrolactone possesses two stereogenic centres and two reactive functionalities (an alcohol and an ester group). Additionally, this compound has a similar structure to γ-butyrolactone (GBL) which is psychoactive. In the present work, biotransformation using seven yeast strains was used to obtain anti stereoisomers of α’-1’-hydroxyethyl-γ-butyrolactone. The process was carried out in both growing and resting culture. The effect of media composition and organic solvent addition on stereoselectivity and effectiveness of biotransformation was also studied. After one day of transformation, optically pure (3R,1’R)-hydroxylactone was obtained by means of Yarrowia lipolytica P26A in YPG medium (yeast extract (1%), peptone (2%) and glucose (2%)). In turn, the use of resting cells culture of Candida viswanathi AM120 in the presence of 10% DES (deep eutectic solvent) allowed us to obtain a (3S,1’S)-enantiomer with de = 85% (diastereomeric excess) and ee 76% (enantiomeric excess). Full article

The use of pheromones in the integrated pest management of insects is currently considered a sustainable and environmentally benign alternative to hazardous insecticides. 4-Methylheptan-3-ol is an interesting example of an insect pheromone, because its stereoisomers are active towards different species. All four possible stereoisomers of this compound were prepared from 4-methylhept-4-en-3-one by a one-pot procedure in which the two stereogenic centres were created during two sequential reductions catalysed by an ene-reductase (ER) and an alcohol dehydrogenase (ADH), respectively. Full article

Stable hemiaminals can be obtained in the one-pot reaction between 2-aminopyrimidine and nitrobenzaldehyde derivatives. Ten new hemiaminals have been obtained, six of them in crystal state. The molecular stability of these intermediates results from the presence of both electron-withdrawing nitro groups as substituents on the phenyl ring and pyrimidine ring, so no further stabilisation by intramolecular interaction is required. Hemiaminal molecules possess a tetrahedral carbon atom constituting a stereogenic centre. As the result of crystallisation in centrosymmetric space groups both enantiomers are present in the crystal structure. Full article

Under neutral conditions the reactions between 4-amino-1,2,4-triazole and cyano-substituted benzaldehyde derivatives yield stable hemiaminals. Addition of small amounts of acid catalyst promotes further step of dehydration resulting in formation of Schiff bases. Four new hemiaminals and the corresponding imines have been obtained. The molecular stability of the hemiaminal intermediates results from both the 1,2,4-triazole moiety and electron withdrawing substituents on the phenyl ring, so no further stabilisation by intramolecular interaction is required. Hemiaminal molecules possess stereogenic centres on carbon and nitrogen atoms. The chirality of these centres is strongly correlated with the conformation of the molecules due to heteroatom hyperconjugation effects. Full article

Since its identification in the early 1970s, artemisinin, as well as semi-synthetic derivatives and synthetic trioxanes, have been used in malaria therapy. Reduction of artemisinin by NaBH₄ produced dihydroartemisinin (DHA), and yielded a new stereochemically labile centre at C-10, which, in turn, provided two interconverting lactol hemiacetal epimers (namely a and b), whose rate of interconversion depends on buffer, pH, and solvent polarity. Since interconversion of the two epimers occurred on a chromatographic time-scale, this prompted a thorough investigation of the phenomenon as a crucial requisite of any analytical method aimed at quantitating this family of drugs. In this critical review we discuss the current importance of the on-column epimerization of DHA in the development of analytical methods aimed at quantifying the drug, with the purpose of identifying the optimal conditions to minimize on-column epimerization while achieving the best selectivity and efficiency of the overall separation. Full article

The absolute configuration at two newly formed stereogenic centres (5S, 7S) during the key steps of the total synthesis of naturally occuring goniothalesdiol was established by single-crystal X-ray diffraction analysis relative to stereocentres (1S, 8R) of the title compound (alternatively named 3,6-anhydro-2-deoxy-6-phenyl-L-ido-1,4-hexonolactone, C₁₂H₁₂O₄). The conformation of both 5-membered lactone and furanose fused rings is also discussed. Full article