Bicyclic and tricyclic analogues of anthramycin

Diversity-Oriented Synthesis of Benzo[f][1,4]oxazepine-, 2H-Chromene-, and 1,2-Dihydroquinoline-Fused Polycyclic Nitrogen Heterocycles under Microwave-Assisted Conditions

An efficient, diversity-oriented synthesis of oxazepino[5,4-b]quinazolin-9-ones, 6H-chromeno[4,3-b]quinolines, and dibenzo[b,h][1,6]naphthyridines was established involving a substrate-based approach under microwave-assisted and conventional heating conditions in high yields (up to 88%). The CuBr₂-catalyzed, chemoselective cascade annulation of O-propargylated 2-hydroxybenzaldehydes and 2-aminobenzamides delivered oxazepino[5,4-b]quinazolin-9-ones involving a 6-exo-trig cyclization-air oxidation-1,3-proton shift-7-exo-dig cyclization sequence. This one-pot process showed excellent atom economy (-H₂O) and constructed two new heterocyclic rings (six- and seven-membered) and three new C-N bonds in a single synthetic operation. On the other side of diversification, the reaction between O/N-propargylated 2-hydroxy/aminobenzaldehydes and 2-aminobenzyl alcohols delivered 6H-chromeno[4,3-b]quinolines and dibenzo[b,h][1,6]naphthyridines involving sequential imine formation-[4 + 2] hetero-Diels-Alder reaction-aromatization steps. The influence of microwave assistance was superior to conventional heating, where the reactions were clean, rapid, and completed in 15 min, and the conventional heating required a longer reaction time at a relatively elevated temperature.

Synthetic aspects of 1,4- and 1,5-benzodiazepines using o-phenylenediamine: a study of past quinquennial

Benzodiazepines, seven-membered heterocyclic compounds having two nitrogen atoms at different positions, are ruling scaffolds in the area of pharmaceutical industry. They act as cardinal moieties in organic synthesis as well as in medicinal chemistry. Among the different benzodiazepines, 1,4- and 1,5-benzodiazepines play a far-reaching role in the field of biological activities such as anticonvulsion, anti-anxiety, sedation, and hypnotics. In the past few decades, researchers have conducted a lot of work on these moieties and developed broad, valuable, and significant approaches for their synthesis. In this review article, we recapitulate the systematic synthetic strategies of 1,4- and 1,5-benzodiazepines using o-phenylenediamine as a precursor over the past five years (2018-2022). This article will be helpful for scientists and researchers to examine and explore novel and efficient methods for the synthesis of these biologically active moieties.

Microwave-Assisted Copper(II)-Catalyzed Cascade Cyclization of 2-Propargylamino/Oxy-Arylaldehydes and O-Phenylenediamines: Access to Densely Functionalized Benzo[f]Imidazo[1,2-d][1,4]Oxazepines and Benzo[f]Imidazo[1,2-d][1,4]Diazepines

A highly efficient microwave-assisted copper(II)-catalyzed cyclization cascade was established starting from readily accessible O/N-propargylated 2-hydroxy or 2-aminobenzaldehydes and o-phenylenediamines to synthesize densely functionalized imidazo[1,2-d][1,4]oxazepines and imidazo[1,2-d][1,4]diazepines in high yields (up to 93%). This one-pot two-step process was found to be highly atom economical (-H₂O, -H₂) and operationally simple and enabled the generation of two new heterocycle rings (seven- and five-membered) and three new C-N bonds in a single synthetic operation. These reactions well tolerated a variety of substituents including electron-donating and electron-withdrawing groups and furnished the desired fused heterocycles in high yields under microwave irradiation in a very short reaction time. The mechanism of the established protocol involves sequential imine formation-intramolecular cyclization-air oxidation followed by 7-exo-dig cyclization steps. A comparative study between the microwave-assisted approach and conventional heating was also performed to demonstrate the advantages of the microwave-assisted protocol in terms of high yield and shorter reaction time.

Palladium-Catalyzed Benzodiazepines Synthesis

This review is focused on palladium-catalyzed reactions as efficient strategies aimed at the synthesis of different classes of benzodiazepines. Several reaction typologies are reported including hydroamination, amination, C–H arylation, N-arylation, and the Buchwald–Hartwig reaction, depending on the different substrates identified as halogenated starting materials (activated substrates) or unactivated unsaturated systems, which then exploit Pd(0)- or Pd(II)-catalytic species. In particular, the use of the domino reactions, as intra- or intermolecular processes, are reported as an efficient and eco-compatible tool to obtain differently functionalized benzodiazepines. Different domino reaction typologies are the carboamination, aminoarylation, aminoacethoxylation, aminohalogenation, and aminoazidation.

Pyrrolobenzodiazepine Dimers as Antibody–Drug Conjugate (ADC) Payloads

The pyrrolobenzodiazepine (PBD) ring system was first discovered in the 1960s and is found in several naturally occurring potent anti-tumour antibiotics. The mode of action of PBDs involves sequence-selective [purine–guanine–purine (PuGPu)] alkylation in the minor groove of DNA through covalent binding from guanine N2 to the PBD C11-position. Dimerization of the PBD ring system gives molecules that can cross-link DNA, which leads to a substantial increase in potency and DNA binding affinity and an extension of sequence-selectivity compared with monomers. PBD dimers feature as the cytotoxic component of numerous ADCs being evaluated in clinical trials. PBD-ADC clinical candidates loncastuximab tesirine, camidanlumab tesirine and rovalpituzumab tesirine employ a PBD N10 linkage while vadastuximab talirine uses a C2-linkage. The PBD dimer scaffold is versatile and offers many opportunities to diversify the ADC platform, with extensive research being performed worldwide to develop the next generation of PBD payload–linker molecules. The search for new PBD payload–linker molecules has mainly focused on changes in payload structure (e.g. PBD C2 modification and macrocyclisation), alternative conjugation strategies (e.g. haloacetamides, ‘click’ approaches and pyridyl disulphides), non-peptide triggers in the linker (e.g. disulphides) and non-cleavable derivatives (i.e. payload release through antibody degradation).

Novel (S)-1,3,4,12a-tetrahydropyrazino[2,1-c][1,4]benzodiazepine-6,12(2H,11H)-dione derivatives: Selective inhibition of MV-4-11 biphenotypic B myelomonocytic leukemia cells' growth is accompanied by reactive oxygen species overproduction and apoptosis

A series of optically pure (R)- and (S)-1,3,4,12a-tetrahydropyrazino[2,1-c][1,4]benzodiazepine-6,12(2H,11H)-dione derivatives was designed and synthesized as novel anthramycin analogues in a three-step, one-pot procedure, and tested for their antiproliferative activity on nine following cell lines: MV-4-11, UMUC-3, MDA-MB-231, MCF7, LoVo, HT-29, A-549, A2780 and BALB/3T3. The key structural features responsible for exhibition of cytotoxic effect were determined: the (S)-configuration of chiral center and the presence of hydrophobic 4-biphenyl substituent in the side chain. Introduction of bromine atom into the 8 position (8g) or substitution of dilactam ring with benzyl group (8m) further improved the activity and selectivity of investigated compounds. Among others, compound 8g exhibited selective cytotoxic effect against MV-4-11 (IC₅₀ = 8.7 μM) and HT-29 (IC₅₀ = 17.8 μM) cell lines, while 8m showed noticeable anticancer activity against MV-4-11 (IC₅₀ = 10.8 μM) and LoVo (IC₅₀ = 11.0 μM) cell lines. The cell cycle arrest in G₁/S checkpoint and apoptosis associated with overproduction of reactive oxygen species was also observed for 8e and 8m.

A catalyst- and solvent-free multicomponent synthesis and docking study of some new antiproliferative N5-allyl-quinolylpyrido[2,3-b][1,4]benzodiazepinone precursors

Heterocycles of this series resemble MDM2 inhibitors.

Biosynthesis, synthesis, and biological activities of pyrrolobenzodiazepines

Pyrrolobenzodiazepines (PBDs) are sequence selective DNA alkylating agents with remarkable antineoplastic activity. They are either naturally produced by actinomycetes or synthetically produced. The remarkable broad spectrum of activities of the naturally produced PBDs encouraged the synthesis of several PBDs, including dimeric and hybrid PBDs yielding to an improvement in the DNA-binding sequence specificity and in the potency of this class of compounds. However, limitation in the chemical synthesis prevented the testing of one of the most potent PBDs, sibiromycin, a naturally produced glycosylated PBDs. Only recently, the biosynthetic gene clusters for PBDs have been identified opening the doors to the production of glycosylated PBDs by mutasynthesis and biosynthetic engineering. This review describes the recent studies on the biosynthesis of naturally produced pyrrolobenzodiazepines. In addition, it provides an overview on the isolation and characterization of naturally produced PBDs, chemical synthesis of PBDs, mechanism of DNA alkylation, and DNA-binding affinity and cytotoxic properties of both naturally produced and synthetic pyrrolobenzodiazepines.

Synthesis of a novel C2/C2'-aryl-substituted pyrrolo[2,1-c][1,4]benzodiazepine dimer prodrug with improved water solubility and reduced DNA reaction rate

A prodrug form (17) of a novel C2/C2'-aryl-substituted pyrrolobenzodiazepine (PBD) dimer (16) has been synthesized by introducing sodium bisulfite groups to the C11/C11'-positions of the parent bis-imine. The prodrug form is highly water soluble, stable in aqueous conditions, and the rate of DNA cross-link formation is much slower compared to the parent bis-imine.

Emerging molecular diversity from the intra-molecular Ugi reaction: iterative efficiency in medicinal chemistry

This review details a now established area within the isonitrile multi-component reaction (IMCR) field of study, namely employing bi-functional reagents in the Ugi reaction for the construction of screening sets with the additional element or even possibly 'metric' of enhanced 'iterative efficiency potential'. The concept of 'iterative efficiency' will be briefly introduced, coupled with discussion on new synthetic routes to select bi-functional IMCR precursors and their use in the generation of pharmacologically relevant 'molecular diversity'.

Solution structure of a 2:1 C2-(2-naphthyl) pyrrolo[2,1-c][1,4]benzodiazepine DNA adduct: molecular basis for unexpectedly high DNA helix stabilization

The naturally occurring pyrrolo[2,1- c][1,4]benzodiazepine (PBD) monomers such as sibiromycin, anthramycin, and tomaymycin form stable covalent adducts with duplex DNA at purine-guanine-purine sites. A correlative relationship between DNA-binding affinity, as measured by enhanced thermal denaturation temperature of calf thymus DNA ( T m), and cytotoxicity is well documented for these naturally occurring compounds and a range of synthetic analogues with sibiromycin having the highest Delta T m value (16.3 degrees C), reflecting favorable hydrogen-bonding interactions between the molecule and DNA bases. We report here that, surprisingly, the structurally simple synthetic C2-(2-naphthyl)-substituted pyrrolo[2,1- c][1,4]benzodiazepine monomer ( 5) has a Delta T m value (15.8 degrees C) similar to that of sibiromycin and significantly higher than the values for either anthramycin (13.0 degrees C) or tomaymycin (2.6 degrees C). 5 also has similar cytotoxic potency to sibiromycin which is widely regarded as the most potent naturally occurring PBD monomer. To investigate this, we have used NMR in conjunction with molecular dynamics to study the 2:1 adduct formed between 5 and the DNA duplex d(AATCTTTAAAGATT) 2. In contrast to the hydrogen-bonding interactions which predominate in the case of sibiromycin and anthramycin adducts, we have shown that the high binding affinity of 5 is due predominantly to hydrophobic (van der Waals) interactions. The high-resolution 2D NOESY, TOCSY, and COSY data obtained have also allowed unequivocal determination of the orientation of the PBD molecule (A-ring toward 3'-end of covalently bound strand), the stereochemistry at the C11 position of the PBD (C11 S), and the conformation of the C2-naphthyl ring which extends along the floor of the minor groove thus optimizing hydrophobic interactions with DNA. These results provide opportunities for future drug design in terms of extending planar hydrophobic groups at the C2 position of PBDs to maximize binding affinity.

Synthesis of a novel C2-aryl pyrrolo[2,1-c][1,4]benzodiazepine-5,11-dione library: Effect of C2-aryl substitution on cytotoxicity and non-covalent DNA binding

A 23-member C2-aryl pyrrolo[2,1-c][1,4]benzodiazepine-5,11-dione (PBD dilactam) library has been synthesized using Suzuki coupling, and the effect of base upon racemisation at the C11a-position during the cross-coupling reaction studied. Three library members (21, 30 and 33) were sufficiently cytotoxic in the NCI's preliminary screen to warrant further evaluation, and one (30, R=p-Br) was found to be cytotoxic at the sub-micromolar level in the A498 renal cancer cell line. DNA thermal denaturation studies suggested that this activity may be associated with non-covalent DNA interaction, and also demonstrated that introduction of C2-C3 unsaturation and addition of C2-aryl functionalities to the PBD dilactam skeleton significantly enhanced helix stabilisation compared to the unsubstituted PBD dilactam (6).

Synthesis of the first example of a C2-C3/C2'-C3'-endo unsaturated pyrrolo[2,1-c][1,4]benzodiazepine dimer

We report the first example of a C2-C3/C2'-C3'-endo unsaturated pyrrolo[2,1-c][1,4]benzodiazepine (PBD) dimer 16 synthesised through a new and efficient route, thus establishing that C2-C3-endo unsaturation enhances both cytotoxicity and DNA-binding affinity in A-Ring-linked PBD dimers but to a lesser extent than C2/C2'-exo-unsaturation. This new route has allowed the preparation of multi-gram quantities of the related clinical candidate 1 and should lead to more structurally diverse PBD dimer analogues.

Effect of C2/C3-endo unsaturation on the cytotoxicity and DNA-binding reactivity of pyrrolo[2,1-c][1,4]benzodiazepines

A series of novel C2,C3-endo unsaturated pyrrolo[2,1-c][1,4]benzodiazepines (PBDs) has been synthesised via cleavage of the N10-Alloc protecting group from appropriate precursors. Biophysical and biological evaluations show that the presence of C2/C3-endo unsaturation in the PBD C-ring enhances both DNA-binding reactivity and in vitro cytotoxic potency.