Synthesis and CHK1 inhibitory potency of Hymenialdisine analogues

De novo design and synthesis of dipyridopurinone derivatives as visible-light photocatalysts in productive guanylation reactions

Described here is the de novo design and synthesis of a series of 6H-dipyrido[1,2-e:2',1'-i]purin-6-ones (DPs) as a new class of visible-light photoredox catalysts (PCs). The synthesized DP1-5 showed their λ _Abs(max) values in 433-477 nm, excited state redox potentials in 1.15-0.69 eV and -1.41 to -1.77 eV (vs. SCE), respectively. As a representative, DP4 enables the productive guanylation of various amines, including 1°, 2°, and 3°-alkyl primary amines, secondary amines, aryl and heteroaryl amines, amino-nitrile, amino acids and peptides as well as propynylamines and α-amino esters giving diversities in biologically important guanidines and cyclic guanidines. The photocatalytic efficacy of DP4 in the guanylation overmatched commonly used Ir and Ru polypyridyl complexes, and some organic PCs. Other salient merits of this method include broad substrate scope and functional group tolerance, gram-scale synthesis, and versatile late-stage derivatizations that led to a derivative 81 exhibiting 60-fold better anticancer activity against Ramos cells with the IC₅₀ of 0.086 μM than that of clinical drug ibrutinib (5.1 μM).

Fused-azepinones: Emerging scaffolds of medicinal importance

Hymenialdisine an alkaloid of oroidin class has drawn the attention of researchers owing to its unique structural features and interesting biological properties. Hymenialdisine exhibited promising inhibitory activity against a number of therapeutically important kinases viz., CDKs, GSK-3β etc., and showed anti-cancer, anti-inflammatory, anti-HIV, neuroprotective, anti-fouling, anti-plasmodium properties. Hymenialdisine and other structurally related oroidin alkaloids such as dibromo-hymenialdisine, stevensine, hymenin, axinohydantoin, spongicidines A-D, latonduines and callyspongisines contain pyrrolo[2,3-c] azepin-8-one core in common. Keeping in view of the interesting structural and therapeutic features of HMD, several structural modifications were carried around the fused-azepinone core which resulted in a number of diverse structural motifs like indolo-azepinones, paullones, aza-paullones, darpones and 5,7-dihydro-6H-benzo[b]pyrimido[4,5-d] azepin-6-one. In this review, an attempt is made to collate and review the structures of diverse hymenialdisine and related fused-azepinones of synthetic/natural origin and their biological properties.

Bioactive pyrrole alkaloids isolated from the Red Sea: marine sponge Stylissa carteri

Fifteen pyrrole alkaloids were isolated from the Red Sea marine sponge Stylissa carteri and investigated for their biological activities. Four of them were dibrominated [(+) dibromophakelline, Z-3-bromohymenialdisine, (±) ageliferin and 3,4-dibromo-1H-pyrrole-2-carbamide], nine compounds were monobrominated [(-) clathramide C, agelongine, (+) manzacidin A, (-) 3-bromomanzacidin D, Z-spongiacidin D, Z-hymenialdisine, 2-debromostevensine, 2-bromoaldisine and 4-bromo-1H-pyrrole-2-carbamide)] and finally, two compounds were non-brominated derivatives viz., E-debromohymenialdisine and aldisine. The structure elucidations of isolated compounds were based on 1D & 2D NMR spectroscopic and MS studies, as well as by comparison with literature. In-vitro, Z-spongiacidin D exhibited a moderate activity on (ARK5, CDK2-CycA, CDK4/CycD1, VEGF-R2, SAK and PDGFR-beta) protein kinases. Moreover, Z-3-bromohymenialdisine showed nearly similar pattern. Furthermore, Z-hymenialdisine displayed a moderate effect on (ARK5 & VEGF-R2) and (-) clathramide C showed a moderate activity on AURORA-A protein kinases. While, agelongine, (+) manzacidin A, E-debromohymenialdisine and 3,4-dibromo-1H-pyrrole-2-carbamide demonstrated only marginal inhibitory activities. The cytotoxicity study was evaluated in two different cell lines. The most effective secondary metabolites were (+) dibromophakelline and Z-3-bromohymenialdisine on L5178Y. Finally, Z-hymenialdisine, Z-3-bromohymenialdisine and (±) ageliferin exhibited the highest cytotoxic activity on HCT116. No report about inhibition of AURORA-A and B by hymenialdisine/hymenialdisine analogs existed and no reported toxicity of ageliferin existed in literature.

Mild one-pot Horner-Wadsworth-Emmons olefination and intramolecular N-arylation for the syntheses of indoles, all regio-isomeric azaindoles, and thienopyrroles

The syntheses of various N-protected aromatic-ring fused pyrrole-2-carboxylate derivatives have been accomplished using mild one-pot Horner-Wadsworth-Emmons olefination and Cu-catalyzed intramolecular N-arylation reactions. The optimized mild one-pot reaction conditions of various 2-bromo arylcarboxaldehydes with commercially available N-protected phosphonoglycine trimethylesters gave the desired aromatic-ring fused pyrrole-2-carboxylates, such as substituted indole-, all regio-isomeric azaindole-, and thienopyrrole-2-carboxylates, in good to excellent yields. These conditions showed broad substrate compatibility, without the loss of the protecting group.

Applications of NMR screening techniques to the pharmaceutical target Checkpoint kinase 1

Ligand screening techniques based on NMR spectroscopy are not as sensitive as other commonly used methods like fluorescence, radiolabeling and surface plasmon resonance. However, using modern NMR instrumentation, they can achieve reliable screening under near physiological condition using as little as 4.6 nmol of receptor and 100 nmol of ligand. Additionally, these NMR methods can also provide valuable and specific information on the ligand under investigation such as the dissociation constant KD, the binding epitope and most importantly some structural information on the actual conformation in the bound state. In this manuscript, we describe the use of NMR based screening techniques ("Saturation Transfer Difference" (STD) and "Water Ligand Observed via Gradient SpectroscopY" (WaterLOGSY)) to detect small therapeutic molecules that interact with the DNA damage checkpoint enzyme Checkpoint kinase 1 (Chk1). After the identification of the most potent ligand, we used specific NMR experiments to perform the epitope mapping of this ligand ("Group epitope mapping-STD" (GEM-STD), "Difference of Inversion REcovery rate with and without Target IrradiatiON" (DIRECTION)) and to characterize its bound conformation ("Transferred-Nuclear Overhauser Effect SpectroscopY" (tr-NOESY), "Transferred-Rotating frame Overhauser Effect SpectroscopY" (tr-ROESY)). Finally, we used molecular docking procedures to position the ligand within the active site of Chk1. On the experimental level, a comparison between NMR studies performed in a 90%H2O/10%D2O buffer and a 100% D2O buffer is also presented and discussed.

Synthetic studies of centromere-associated protein-E (CENP-E) inhibitors: 1.Exploration of fused bicyclic core scaffolds using electrostatic potential map

Centromere-associated protein-E (CENP-E), a mitotic kinesin that plays an important role in mitotic progression, is an attractive target for cancer therapeutic drugs. For the purpose of developing novel CENP-E inhibitors as cancer therapeutics, we investigated a fused bicyclic compound identified by high throughput screening, 4-oxo-4,5-dihydrothieno[3,4-c]pyridine-6-carboxamide 1a. Based on this scaffold, we designed inhibitors for efficient binding at the L5 site in CENP-E utilizing homology modeling as well as electrostatic potential map (EPM) analysis to enhance CENP-E inhibitory activity. This resulted in a new lead, 5-bromoimidazo[1,2-a]pyridine 7, which showed potent CENP-E enzyme inhibition (IC50: 50nM) and cellular activity with accumulation of phosphorylated histone H3 in HeLa cells. Our homology model and EPM analysis proved to be useful tools for the rational design of CENP-E inhibitors.

Leucettines, a class of potent inhibitors of cdc2-like kinases and dual specificity, tyrosine phosphorylation regulated kinases derived from the marine sponge leucettamine B: modulation of alternative pre-RNA splicing

We here report on the synthesis, optimization, and biological characterization of leucettines, a family of kinase inhibitors derived from the marine sponge leucettamine B. Stepwise synthesis of analogues starting from the natural structure, guided by activity testing on eight purified kinases, led to highly potent inhibitors of CLKs and DYRKs, two families of kinases involved in alternative pre-mRNA splicing and Alzheimer's disease/Down syndrome. Leucettine L41 was cocrystallized with CLK3. It interacts with key residues located within the ATP-binding pocket of the kinase. Leucettine L41 inhibits the phosphorylation of serine/arginine-rich proteins (SRp), a family of proteins regulating pre-RNA splicing. Indeed leucettine L41 was demonstrated to modulate alternative pre-mRNA splicing, in a cell-based reporting system. Leucettines should be further explored as pharmacological tools to study and modulate pre-RNA splicing. Leucettines may also be investigated as potential therapeutic drugs in Alzheimer's disease (AD) and in diseases involving abnormal pre-mRNA splicing.

Molecular and cellular pharmacological properties of 5-methoxycarbonylamino-N-acetyltryptamine (MCA-NAT): a nonspecific MT3 ligand

5-Methoxycarbonylamino-N-acetyltryptamine (MCA-NAT) has been initially described as a ligand at non MT(1), non MT(2) melatonin binding site (MT3) selective versus MT(1) and MT(2), two membrane melatonin receptors. MCA-NAT activity has been reported by others in different models, in vivo, particularly in the intra-ocular pressure (IOP) models in rabbits and monkeys. Its activity was systematically linked to either MT3 or to a new, yet unknown, melatonin receptor. In this article, the melatonin receptor pharmacology of MCA-NAT is described. MCA-NAT has micromolar range affinities at the melatonin receptors MT(1) and MT(2), while in functional studies, MCA-NAT proved to be a powerful MT(1)/MT(2) partial agonist in the sub-micromolar range. These data strongly suggest that MCA-NAT actions might be mediated by these receptors in vivo. Finally, as described by others, we show that MCA-NAT is unable to elicit any type of receptor-like functional responses from Chinese hamster ovary cells over-expressing quinone reductase 2, the MT3.

A submarine journey: the pyrrole-imidazole alkaloids

In his most celebrated tale "The Picture of Dorian Gray", Oscar Wilde stated that "those who go beneath the surface do so at their peril". This sentence could be a prophetical warning for the practitioner who voluntarily challenges himself with trying to synthesize marine sponge-deriving pyrrole-imidazole alkaloids. This now nearly triple-digit membered community has been growing exponentially in the last 20 years, both in terms of new representatives and topological complexity--from simple, achiral oroidin to the breathtaking 12-ring stylissadines A and B, each possessing 16 stereocenters. While the biosynthesis and the role in the sponge economy of most of these alkaloids still lies in the realm of speculations, significant biological activities for some of them have clearly emerged. This review will account for the progress in achieving the total synthesis of the more biologically enticing members of this class of natural products.