A-ring Modifications Research Articles

Asymmetric synthesis of phthalascidin, zalypsis and renieramycin T from N-Cbz-L-tyrosine

A new practical synthesis of Pt-650, zalypsis and renieramycin T is achieved by employing a Pictet−Spengler cyclization coupling of the tetrahydroisoquinoline and phenylalaninol partners with good yield and reproducibility, in which both the two coupling partners are prepared by a common route. Moreover, a one-pot Mitsunobu displacement/photolysis sequence of methoxyquinone alcohol intermediate implements the introduction of the amino functionality at C-22 and A-ring modification in one step. By the approach, Pt-650, zalypsis and renieramycin T are synthesized with 21–24 total synthetic steps from N-Cbz-l-tyrosine in good overall yield respectively.

Abstract 3107: Development of novel JAK2 inhibitors and PROTACs as chemical probes for the investigation of JAK2 inhibition and degradation

Abstract Inhibition and, more recently, degradation of protein kinases is an important therapeutic strategy to modulate disregulated signaling pathways in the cell cycle. Janus kinase 2 (JAK2) is a protein kinase involved in the JAK/STAT pathway which is one of the 12 core cancer pathways; thus, the regulation of JAK2 is important in the maintenance of normal cell function. A fragment-based drug discovery approach was taken to synthesize novel JAK2 inhibitors based using building blocks suitable for PROTAC development. Small molecule inhibitors were analyzed through computational analysis to probe the binding interactions in the hinge region of the ATP active site of JAK2. PROTACs were designed to investigate the degradation of JAK2 based on small molecule ligands with high binding affinity to JAK2. Pyrrolopyrimidine and pyrimidine scaffolds were used to probe the hydrogen bonding interactions in the hinge region to investigate binding affinity. Modification of A-ring and B-ring fragments of the inhibitors and PROTACs were used to develop SAR through data obtained by functional assays, including differential scanning fluorimetry and 33P HotSpot™ kinase assay, in addition to in-vivo cell viability assays as models for myeloproliferative neoplasms. Several key pyrrolopyrimidine and pyrimidine core containing inhibitors and PROTACs bind strongly to JAK2 and modulate JAK2 activity in appropriate cancer cell lines. Citation Format: Briley A. Humphrey, Bao li, Renan B. Ferreira, Sujeewa R. Ranatunga, Tegan M. Rowsell, Luxin Sun, Harshani R. Lawrence, Ernst Schonbrunn, Gary Reuther, Nicholas J. Lawrence. Development of novel JAK2 inhibitors and PROTACs as chemical probes for the investigation of JAK2 inhibition and degradation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3107.

Structural optimizations and bioevaluation of N-H aporphine analogues as Gq-biased and selective serotonin 5-HT2C receptor agonists

The concept of subtype selectivity and functional bias has recently reshaped current GPCR drug discovery for G protein-coupled receptors. A series of new N-H aporphines with A-ring modifications have been synthesized, and their efficacy on 5-HT2 receptor activation was evaluated. SAR analysis led to the discovery of several more potent and selective 5-HT2C receptor agonists (e.g., 11b and 11f) with low nanomolar activity. Molecular docking analysis of this series of aporphines was in accordance with our SAR results. The functional selectivity of specific compounds was tested via both Gq-mediated calcium flux and β-arrestin recruitment assays, which revealed that these compounds exhibited no β-arrestin recruitment activity. Further ADMET study combined with behavioral assessment using a methamphetamine-induced hyperactivity model identified compound 11b and 11f possessing promising drug-like profiles and having antipsychotic potential. These agonists with an exclusive bias toward Gq signaling may serve as valuable pharmacological probes to facilitate the elucidation of therapeutically relevant 5-HT2C signaling pathways and the development of alternative antipsychotic medications.

Steroid Metabolism in Thermophilic Actinobacterium Saccharopolyspora hirsuta VKM Ac-666T.

The application of thermophilic microorganisms opens new prospects in steroid biotechnology, but little is known to date on steroid catabolism by thermophilic strains. The thermophilic strain Saccharopolyspora hirsuta VKM Ac-666T has been shown to convert various steroids and to fully degrade cholesterol. Cholest-4-en-3-one, cholesta-1,4-dien-3-one, 26-hydroxycholest-4-en-3-one, 3-oxo-cholest-4-en-26-oic acid, 3-oxo-cholesta-1,4-dien-26-oic acid, 26-hydroxycholesterol, 3β-hydroxy-cholest-5-en-26-oic acid were identified as intermediates in cholesterol oxidation. The structures were confirmed by 1H and 13C-NMR analyses. Aliphatic side chain hydroxylation at C26 and the A-ring modification at C3, which are putatively catalyzed by cytochrome P450 monooxygenase CYP125 and cholesterol oxidase, respectively, occur simultaneously in the strain and are followed by cascade reactions of aliphatic sidechain degradation and steroid core destruction via the known 9(10)-seco-pathway. The genes putatively related to the sterol and bile acid degradation pathways form three major clusters in the S. hirsuta genome. The sets of the genes include the orthologs of those involved in steroid catabolism in Mycobacterium tuberculosis H37Rv and Rhodococcus jostii RHA1 and related actinobacteria. Bioinformatics analysis of 52 publicly available genomes of thermophilic bacteria revealed only seven candidate strains that possess the key genes related to the 9(10)-seco pathway of steroid degradation, thus demonstrating that the ability to degrade steroids is not widespread among thermophilic bacteria.

Cytochrome P450 Hydroxylase TnmL Catalyzing Sequential Hydroxylation with an Additional Proofreading Activity in Tiancimycin Biosynthesis.

Tiancimycin (TNM) A belongs to the anthraquinone-fused subfamily of enediyne natural products, and selected enediynes have been translated into clinical drugs. Previously, inactivation of tnmL in Streptomyces sp. CB03234 resulted in the accumulation of TNM B and TNM E, supporting the functional assignment of TnmL as a cytochrome P450 hydroxylase that catalyzes A-ring modification in TNM A biosynthesis. Herein, we report in vitro characterization of TnmL, revealing that (i) TnmL catalyzes two successive hydroxylations of TNM E, resulting in sequential production of TNM F and TNM C, (ii) TnmL shows a strict substrate preference, with the C-26 side chain playing a critical role in substrate binding, and (iii) TnmL demethylates the C-7 OCH3 group of TNM G, affording TNM F, thereby channeling the shunt product TNM G back into TNM A biosynthesis and representing a rare proofreading logic for natural product biosynthesis. These findings shed new insights into anthraquinone-fused enediyne biosynthesis.

SYNTHESIS, ACETYLCHOLINESTERASE AND BUTYRYLCHOLINESTERASE INHIBITORY ACTIVITY OF NOVEL TRICYCLIC 1-PHENYL-1,6,7,8-TETRAHYDRO-4H- PYRAZOLO[3,4-d]PYRROLO[1,2-a]PYRIMIDIN-4-ONE

A convenient synthesis of novel tricyclic annulated pyrimidinone, namely 1-phenyl- 1,6,7,8-tetrahydro-4 H -pyrazolo[3,4- d ]pyrrolo[1,2- a ]pyrimidin-4-one was described herein. Cyclization was provided via A-ring modification of deoxyvasicinone (natural product). Biological activities of this compound reveal promising acetylcholinesterase inhibitory activity of 82.48±0.76 %, while showed moderate butyrylcholinesterase inhibitory activity

Synthesis and characterization of 20-hydroxyvitamin D3 with the A-ring modification

Two novel 20-hydroxyvitamin D3 analogues (4a,b) with the A-ring modification have been synthesized by a convergent manner. An alternative pathway of vitamin D3 metabolism by cytochrome P450scc CYP11A1 was reported to afford 20-hydroxyvitamin D3 (3), functions of which remain to be explored. Based on the structure of the 20-hydroxy metabolite, novel analogues (4a,b) with the modifications, including the 1α-hydroxy, 25-hydroxy and 2α-methyl groups, have been designed. The side chain of the requisite CD-ring portions (9a,b) was introduced by Grignard reaction as a key step, and the stereochemistry at the C20 position was confirmed by the X-ray crystal structure analysis of the synthetic intermediate (8b). Preliminary biological characterization using the bovine thymus vitamin D receptor suggested that the introduction of the active motifs into the 20-hydroxyvitamin D3 scaffold elevated the receptor affinity.

Direct sequential C-H iodination/organoyl-thiolation for the benzenoid A-ring modification of quinonoid deactivated systems: a new protocol for potent trypanocidal quinones.

We report a sequential C-H iodination/organoyl-thiolation of naphthoquinones and their relevant trypanocidal activity. Under a combination of AgSR with a copper source, sulfur-substituted benzenoid quinones were prepared in high yields (generally >90%). This provides an efficient and general method for preparing A-ring modified naphthoquinoidal systems, recognized as a challenge in quinone chemistry.

Friedelane triterpenoids: transformations toward A-ring modifications including 2-homoderivatives

Common reaction strategies were employed on suitable substrates to achieve a series of C2,C3-; C3,C4- and C2,C3,C4-functionalized (including 2-homo-) friedelane triterpenoids with just one to four efficient steps.

Synthetic strategy and biological activity of A-ring stereoisomers of 1,25- dihydroxyvitamin D3 and C2-modified analogues.

The hormonally active form of vitamin D3, 1α,25-dihydroxyvitamin D3 (1a), has a wide variety of biological activities and its major molecular target is considered to be the vitamin D receptor (VDR). The A-ring stereoisomers of 1a as well as its C2-modified analogues, which have different stereochemistry at the C1 and/or C3 hydroxy groups, are of interest since recent metabolic studies have shown that catabolism could occur through A-ring modification. In this review, a practical and versatile synthesis of the A-ring enyne precursors by the convergent method of Trost and coworkers, which is needed to construct all possible A-ring stereoisomers of 1,25-dihydroxyvitamin D3 (1a-d), and the C2-modified analogues (4a-d, 5a-d, 6a-d and 7a-d) is described. A strategy for the synthesis and evaluation of all possible A-ring stereoisomers of 1a and their A-ring modified analogues is important, and this will stimulate synthesis and biological studies into vitamin D.

Design, synthesis, and biological evaluation of stable colchicine binding site tubulin inhibitors as potential anticancer agents.

To block the metabolically labile sites of novel tubulin inhibitors targeting the colchicine binding site based on SMART, ABI, and PAT templates, we have designed, synthesized, and biologically tested three focused sets of new derivatives with modifications at the carbonyl linker, the para-position in the C ring of SMART template, and modification of A ring of the PAT template. Structure–activity relationships of these compounds led to the identification of new benzimidazole and imidazo[4,5-c]pyridine-fused ring templates, represented by compounds 4 and 7, respectively, which showed enhanced antitumor activity and substantially improved the metabolic stability in liver microsomes compared to SMART. MOM group replaced TMP C ring and generated a potent analogue 15, which showed comparable potency to the parent SMART compound. Further modification of PAT template yielded another potent analogue 33 with 5-indolyl substituent at A ring.

Design and synthesis of lupeol analogues and their in vitro PTP-1B inhibitory activity

Synthetic analogues of the naturally occurring triterpenoid, lupeol by modification of A-ring and isopropylene moiety with different carboxylic acid functionalities and their biological activity were investigated. The analogues were designed by considering the incorporation of ester and amide linkages in the parent molecule. They were assayed for protein tyrosine phosphatase-1B (PTP-1B) inhibitory activity. Among them, compounds 9a, 9b, 14a, 14b and 14c showed significant dose-dependant inhibition at 10 μM concentration. Our report is marked by readily accessible synthesis, excellent yield and significant PTP-1B inhibitory effect. A synthetic approach and in vitro PTP-1B inhibition of novel analogues of lupeol are described. Compounds 9a, 9b, 14a, 14b and 14a represent a new class of PTP-1B inhibitors in type 2 diabetes

Antimitotic and vascular disrupting agents: 2-Hydroxy-3,4,5-trimethoxybenzophenones

2-Hydroxy-3,4,5-trimethoxybenzophenones (8–16) manifest pseudo-ring formation involving intramolecular hydrogen bonding of the 2-OH and the carbonyl group. Among the synthetic products described in this report, (3-hydroxy-4-methoxyphenyl)(2-hydroxy-3,4,5-trimethoxyphenyl)-methanone (14) and (3-amino-4-methoxyphenyl)(2-hydroxy-3,4,5-trimethoxy-phenyl)methanone (16) exhibit significant antiproliferative activity against KB cells with IC50 values of 11.1 and 11.3 nM, respectively. These two compounds also displayed tubulin affinity comparable to that of combretastatin A-4. In studies with human umbilical vein endothelial cells, compounds 14 and 16 revealed concentration-dependent vascular-disrupting properties. The results support the rationale of the pseudo-ring concept and suggest further investigation of A-ring modification in these benzophenones.

Synthesis of vitamin D3 analogues with A-ring modifications to directly measure vitamin D levels in biological samples

C-3-substituted 25-hydroxyvitamin D3 analogues were synthesized as tools to directly measure levels of vitamin D in biological samples. The strategy involves vinyloxycarbonylation of the 3β-hydroxy group and formation of a carbamate bond with a hydroxyl or amino group at the end of the alkyl chain. Biotinylated conjugates of synthesized derivatives were generated to be linked with vitamin D binding protein (DBP). The spacer group present in the alkyl chain is important in the binding of antibodies to the analogue–DBP complex. When compared to 25-hydroxyvitamin D3-DBP, the binding of some antibodies to the analogue–DBP complex of the 25-hydroxyvitamin D3 derivative 10 that posses an 8-aminoctyl alkyl chain is significantly reduced, but this analogue displaced [26,27-3H]-25-hydroxyvitamin D3 from DBP. In contrast, the 8-hydroxyoctyl alkyl chain analogue 9 showed less displacement.

Synthesis of quinoidal molecules: Strategies towards bioactive compounds with an emphasis on lapachones

Naphthoquinoidal compounds are of great interest in medicinal chemistry. In recent years, several synthetic routes have been developed to obtain bioactive molecules derived from lapachones. In this mini-review, we focus on the synthetic aspects and strategies used to design these compounds and on the biological activities of these substances for the development of drugs against the neglected diseases leishmaniasis and Chagas disease as well as malaria, tuberculosis and cancer. Three strategies used to develop bioactive naphthoquinoidal compounds are discussed: (i) C-ring modification, (ii) redox centre modification and (iii) A-ring modification. Among these strategies, reactions such as copper-catalysed azide–alkyne cycloaddition (click chemistry), palladium-catalysed cross couplings, and heterocyclisations will be discussed for the development of naphthoquinoidal compounds against Trypanosoma cruzi, Leishmania and cancer. The aim of derivatisation is the generation of novel molecules that inhibit cellular organelles/processes, generate reactive oxygen species (ROS) and increase lipophilicity to enhance penetration through the plasma membrane. Modified lapachones have emerged as promising prototypes for the development of drugs against neglected diseases and cancer.

A-ring modification of SCH 900229 and related chromene sulfone γ-secretase inhibitors

Attempts to block metabolism by incorporating a 9-fluoro substituent at the A-ring of compound 1 (SCH 900229) using electrophilic Selectfluor™ led to an unexpected oxidation of the A-ring to give difluoroquinone analog 1a. Oxidation of other related chromene γ-secretase inhibitors 2–8 resulted in similar difluoroquinone analogs 2a–8a, respectively. These quinone products exhibited comparable in vitro potency in a γ-scretase membrane assay, but were several fold less potent in a cell-based assay in lowering Aβ40–42, compared to their parent compounds.

A-ring modifications on the triazafluorenone core structure and their mGluR1 antagonist properties

A-ring modifications on the triazafluorenone core structure were investigated. Five membered heterocycles such as pyrazoles and isothiazoles are not tolerated. It has been found that the pyrimidine nucleus was very well tolerated on the left hand side. Amino pyrimidine compounds 24 and 27 showed acceptable PK profile with significant brain penetration. Compound 9 served as a versatile intermediate for a number of chemical transformations.

Synthesis and biological activity of previtamin D 3 analogues with A-ring modifications

Synthesis of two novel 6- s- cis analogues of 1α,25-dihydroxyvitamin D 3 are described using shikimic acid and its 4- epi isomer as versatile chiral starting materials. These derivatives contain a 2β-(3′-hydroxypropoxy) moiety or a 2β,3β-epoxy group into 1α,25-(OH) 2-19- nor-pre-D 3. The synthesized analogues were found to be not suitable for binding to the vitamin D receptor and showed weak binding affinity toward the vitamin D-binding protein. The new derivatives failed to inhibit cell proliferation.

Chemical modifications of natural triterpenes—glycyrrhetinic and boswellic acids: evaluation of their biological activity

Synthetic analogues of naturally occurring triterpenoids; glycyrrhetinic acid, arjunolic acid, and boswellic acids, by modification of A-ring with a cyano- and enone-functionality, have been reported. A novel method of synthesis of α-cyanoenones from isoxazoles is reported. Bioassays using primary mouse macrophages and tumor cell lines indicate potent anti-inflammatory and cytotoxic activities associated with cyano-enones of boswellic acid and glycyrrhetinic acid.

2-Substituted-16-ene-22-thia-1α,25-dihydroxy-26,27-dimethyl-19-norvitamin D 3 analogs: Synthesis, biological evaluation, and crystal structure

Recently, we have found that 16-ene-22-thia-26,27-dimethyl-19-norvitamin D 3 analogs 1a ( n = 2, 3) are 20 times more active than the natural hormone 1α,25-dihydroxyvitamin D 3 in terms of transcriptional activity. To further investigate the effects of the A-ring modification of 1a, b on the biological activity profile, novel 22-thia-19-norvitamin D analogs 2– 11 bearing a hydroxyethoxy-, hydroxyethylidene- or methyl group at C-2 in combination with 20 S- and 20 R-isomers were prepared and tested for their in vitro biological activities. All of the synthesized analogs showed 0.5–140% of the activity of the natural hormone in binding to the vitamin D receptor (VDR). When compared with the transcriptional activity of C-2 or C-20 isomeric pairs of the 22-thia analogs, the 20 S-isomers 2– 11a were more potent than the 20 R-isomers 2, 3, 8– 11b, and the 2β-hydroxyethoxy, 2 E-hydroxyethylidene, and 2α-methyl-2β-hydroxy-22-thia isomers showed higher potency than their corresponding counterparts. In particular, 3a exhibited an extremely higher level of potency (210-fold) than the natural hormone. To elucidate the action mode of superagonist 3a at the molecular level, we determined the crystal structures of the rat VDR-ligand-binding domain complexed with 3a or 3b in the presence of peptide containing a nuclear box motif (LxxLL) at 1.9–2.0 Å resolution. The crystal structures demonstrated that the 1α-OH, 3β-OH, and 25-OH groups of the natural hormone and 3a were anchored by the same amino acid residues in the ligand-binding pocket, and the terminal OH moiety of the substituent at C-2 formed hydrogen bonds with Arg270 and a water molecule to create a tight water molecule network. Moreover, the methyl groups at C-26a and C-27a make additional contact with hydrophobic residues such as Leu223, Ala227, Val230, and Ala299. These hydrophilic and hydrophobic interactions in 3a may underlie the induction of superagonistic activity.