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Advances in Synthesis and Biological Activity of Novel Derivatives Based on Five-Membered Heterocyclic Scaffolds and Their Intermediates

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A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Organic Chemistry".

Deadline for manuscript submissions: closed (15 September 2023) | Viewed by 32499

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Dr. Theodora Venera Apostol

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Faculty of Pharmacy, “Carol Davila” University of Medicine and Pharmacy, 020956 Bucharest, Romania
Interests: organic chemistry; heterocycle chemistry; medicinal chemistry; organic synthesis and structure elucidation; 1,3-oxazole; N-acyl-α-amino acid; α-acylamino ketone; diphenyl sulfone scaffold
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Prof. Dr. George Mihai Nitulescu

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Faculty of Pharmacy, “Carol Davila” University of Medicine and Pharmacy, 6 Traian Vuia Street, 020956 Bucharest, Romania
Interests: the design and synthesis of new anticancer agents; the design and synthesis of new antimicrobial compounds; studies and structural analysis; the isolation and analysis of natural compounds with anticancer effects; computer-assisted drug design studies
Special Issues, Collections and Topics in MDPI journals

Prof. Dr. Laura Ileana Socea

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Faculty of Pharmacy, “Carol Davila” University of Medicine and Pharmacy, 020956 Bucharest, Romania
Interests: organic chemistry; organic synthesis and structural analysis; medicinal chemistry; 5H-dibenzo[a,d][7]annulene; hydrazone; hydrazinecarbothioamide; 1,2,4-triazole; 1,3,4-oxadiazole
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

The five-membered heterocyclic compounds (imidazoles, pyrazoles, oxazoles, thiazoles, triazoles, oxadiazoles, thiadiazoles, etc.) are very important in pharmaceutical and medicinal chemistry, as it is known that representatives of this class are the basis of many drugs with various therapeutic actions, including antimicrobial, antiviral, anticancer, anti-inflammatory, analgesic, and antidiabetic activities. Currently, this field is being studied extensively by a large number of researchers in order to discover and develop new pharmaceutical agents and bioactive molecules. Thus, recent progress in synthetic approaches to nitrogen-, oxygen-, and sulfur-containing five-membered heterocycles include different synthesis protocols, such as multi-step strategies, multi-component pathways, photocatalysis, click reaction, microwave-assisted, and green synthesis, with pharmacologically potent derivatives reported.

This Special Issue aims to provide a survey of the recent advances in the synthesis and biological activity of novel derivatives based on five-membered heterocyclic scaffolds and their intermediates (N-acyl-α-amino acids, α-acylamino ketones, acyl hydrazones, acyl thioureas, hydrazinecarbothioamides, isocyanates, isothiocyanates, etc.). We invite you to contribute original research articles and/or reviews of the current scientific literature to this Special Issue of Molecules focused on the design, obtainment, and biological activity assessment of new pentatomic heterocyclic scaffolds and their intermediates.

Dr. Theodora Venera Apostol
Prof. Dr. George Mihai Nitulescu
Prof. Dr. Laura Ileana Socea
Guest Editors

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Keywords

bioactive heterocycles
heterocyclic scaffolds
bioisosteric heterocyclic skeletons
azoles
pyrazole
oxazole
triazole
oxadiazole
drug design
in silico studies

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Advances in Synthesis and Biological Activity of Novel Derivatives Based on Five-Membered Heterocyclic Scaffolds and Their Intermediates—Second Edition in Molecules (7 articles)

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Research

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22 pages, 3205 KiB

Open AccessArticle

Novel 1,2,3-Triazole-Containing Quinoline–Benzimidazole Hybrids: Synthesis, Antiproliferative Activity, In Silico ADME Predictions, and Docking

by Luka Krstulović, Katarina Mišković Špoljarić, Vesna Rastija, Nikolina Filipović, Miroslav Bajić and Ljubica Glavaš-Obrovac

Molecules 2023, 28(19), 6950; https://doi.org/10.3390/molecules28196950 - 6 Oct 2023

Cited by 3 | Viewed by 1591

Abstract

The newly synthesized quinoline–benzimidazole hybrids containing two types of triazole-methyl-phenoxy linkers were characterized via NMR and elemental analysis. Additional derivatization was achieved by introducing bromine at the C-2 position of the phenoxy core. These novel hybrids were tested for their effects on the growth of the non-tumor cell line MRC-5 (human fetal lung fibroblasts), leukemia and lymphoma cell lines: Hut78, THP-1 and HL-60, and carcinoma cell lines: HeLa and CaCo-2. The results obtained, presented as the concentration that achieves 50% inhibition of cell growth (IC₅₀ value), show that the compounds tested affect tumor cell growth differently depending on the cell line and the dose applied (IC₅₀ ranged from 0.2 to >100 µM). The quinoline–benzimidazole hybrids tested, including 7-chloro-4-(4-{[4-(5-methoxy-1H-1,3-benzo[d]imidazol-2-yl)phenoxy]methyl}-1H-1,2,3-triazol-1-yl)quinoline 9c, 2-(3-bromo-4-{[1-(7-chloroquinolin-4-yl)-1H-1,2,3-triazol-4-yl]methoxy}phenyl)-N-propyl-1H-benzo[d]imidazol-5-carboximidamide trihydrochloride 10e, 2-{4-[(1-{2-[(7-chloroquinolin-4-yl)amino]ethyl}-1H-1,2,3-triazol-4-yl)methoxy]phenyl}-N-propyl-1H-benzo[d]imidazol-5-carboximidamide trihydrochloride 14e and 2-{3-bromo-4-[(1-{2-[(7-chloroquinolin-4-yl)amino]ethyl}-1H-1,2,3-triazol-4-yl)methoxy]phenyl}-N-propyl-1H-benzo[d]imidazol-5-carboximidamide trihydrochloride 15e, arrested the cell cycle of lymphoma (HuT78) cells. The calculated ADMET properties showed that the synthesized compounds violated at most two of Lipinski’s rules, making them potential drug candidates, but mainly for parenteral use due to low gastrointestinal absorption. The quinoline–benzimidazole hybrid 14e, which was shown to be a potent and selective inhibitor of lymphoma cell line growth, obtained the highest binding energy (−140.44 kcal/mol), by docking to the TAO2 kinase domain (PDB: 2GCD). Full article

(This article belongs to the Special Issue Advances in Synthesis and Biological Activity of Novel Derivatives Based on Five-Membered Heterocyclic Scaffolds and Their Intermediates)

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29 pages, 5237 KiB

Open AccessArticle

Derivatives Incorporating Acridine, Pyrrole, and Thiazolidine Rings as Promising Antitumor Agents

by Monika Garberová, Ivan Potočňák, Monika Tvrdoňová, Monika Majirská, Martina Bago-Pilátová, Slávka Bekešová, Andrej Kováč, Peter Takáč, Krutika Khiratkar, Zuzana Kudličková, Ján Elečko and Mária Vilková

Molecules 2023, 28(18), 6616; https://doi.org/10.3390/molecules28186616 - 14 Sep 2023

Cited by 1 | Viewed by 1606

Abstract

Derivatives combining acridine, pyrrole, and thiazolidine rings have emerged as promising candidates in the field of antitumor drug discovery. This paper aims to highlight the importance of these three structural motifs in developing potent and selective anticancer agents. The integration of these rings within a single molecule offers the potential for synergistic effects, targeting multiple pathways involved in tumor growth and progression. Spiro derivatives were efficiently synthesized in a two-step process starting from isothiocyanates and 2-cyanoacetohydrazide. The thiourea side chain in spiro derivatives was utilized as a key component for the construction of the thiazolidine-4-one ring through regioselective reactions with bifunctional reagents, namely methyl-bromoacetate, dietyl-acetylenedicarboxylate, ethyl-2-bromopropionate, and ethyl-2-bromovalerate. These reactions resulted in the formation of a single regioisomeric product for each derivative. Advanced spectroscopic techniques, including 1D and 2D NMR, FT-IR, HRMS, and single-crystal analysis, were employed to meticulously characterize the chemical structures of the synthesized derivatives. Furthermore, the influence of these derivatives on the metabolic activity of various cancer cell lines was assessed, with IC₅₀ values determined via MTT assays. Notably, derivatives containing ester functional groups exhibited exceptional activity against all tested cancer cell lines, boasting IC₅₀ values below 10 μM. Particularly striking were the spiro derivatives with methoxy groups at position 3 and nitro groups at position 4 of the phenyl ring. These compounds displayed remarkable selectivity and exhibited heightened activity against HCT-116 and Jurkat cell lines. Additionally, 4-oxo-1,3-thiazolidin-2-ylidene derivatives demonstrated a significant activity against MCF-7 and HCT-116 cancer cell lines. Full article

(This article belongs to the Special Issue Advances in Synthesis and Biological Activity of Novel Derivatives Based on Five-Membered Heterocyclic Scaffolds and Their Intermediates)

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30 pages, 2352 KiB

Open AccessArticle

[1,2,4]triazolo[4,3-a]quinoxaline as Novel Scaffold in the Imiqualines Family: Candidates with Cytotoxic Activities on Melanoma Cell Lines

by Cindy Patinote, Sandy Raevens, Amélie Baumann, Eloise Pellegrin, Pierre-Antoine Bonnet and Carine Deleuze-Masquéfa

Molecules 2023, 28(14), 5478; https://doi.org/10.3390/molecules28145478 - 18 Jul 2023

Cited by 2 | Viewed by 2083

Abstract

Cutaneous melanoma is one of the most aggressive human cancers and is the deadliest form of skin cancer, essentially due to metastases. Novel therapies are always required, since cutaneous melanoma develop resistance to oncogenic pathway inhibition treatment. The Imiqualine family is composed of heterocycles diversely substituted around imidazo[1,2-a]quinoxaline, imidazo[1,2-a]pyrazine, imidazo[1,5-a]quinoxaline, and pyrazolo[1,5-a]quinoxaline scaffolds, which display interesting activities on a panel of cancer cell lines, especially melanoma cell lines. We have designed and prepared novel compounds based on the [1,2,4]triazolo[4,3-a]quinoxaline scaffold through a common synthetic route, using 1-chloro-2-hydrazinoquinoxaline and an appropriate aldehyde. Cyclization is ensured by an oxidation-reduction mechanism using chloranil. The substituents on positions 1 and 8 were chosen based on previous structure–activity relationship (SAR) studies conducted within our heterocyclic Imiqualine family. Physicochemical parameters of all compounds have also been predicted. A375 melanoma cell line viability has been evaluated for 16 compounds. Among them, three novel [1,2,4]triazolo[4,3-a]quinoxalines display cytotoxic activities. Compounds 16a and 16b demonstrate relative activities in the micromolar range (respectively, 3158 nM and 3527 nM). Compound 17a shows the best EC₅₀ of the novel series (365 nM), even if EAPB02303 remains the lead of the entire Imiqualine family (3 nM). Full article

(This article belongs to the Special Issue Advances in Synthesis and Biological Activity of Novel Derivatives Based on Five-Membered Heterocyclic Scaffolds and Their Intermediates)

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18 pages, 3518 KiB

Open AccessArticle

New Chemistry of Chiral 1,3-Dioxolan-4-Ones

by R. Alan Aitken, Lynn A. Power and Alexandra M. Z. Slawin

Molecules 2023, 28(9), 3845; https://doi.org/10.3390/molecules28093845 - 1 May 2023

Cited by 3 | Viewed by 1639

Abstract

(2S,5S)-5-Phenyl-2-t-butyl-1,3-dioxolan-4-one, readily derived from mandelic acid, undergoes the Michael addition to butenolide and 4-methoxy-β-nitrostyrene with the absolute configuration of the products confirmed by X-ray diffraction in each case. In the former case, thermal fragmentation gives the phenyl ketone, thus illustrating use of the dioxolanone as a chiral benzoyl anion equivalent. The Diels–Alder cycloaddition chemistry of (2S)-5-methylene-2-t-butyl-1,3-dioxolan-4-one, derived from lactic acid, has been further examined with the X-ray structures of four adducts determined. In one case, thermal fragmentation of the adduct gives a chiral epoxy ketone resulting from the dioxolanone acting as a chiral ketene equivalent, while in others the products give insight into the mechanism of the dioxolanone fragmentation process. Full article

(This article belongs to the Special Issue Advances in Synthesis and Biological Activity of Novel Derivatives Based on Five-Membered Heterocyclic Scaffolds and Their Intermediates)

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25 pages, 6544 KiB

Open AccessArticle

Design, Synthesis, In Vitro, and In Silico Insights of 5-(Substituted benzylidene)-2-phenylthiazol-4(5H)-one Derivatives: A Novel Class of Anti-Melanogenic Compounds

by Dahye Yoon, Min Kyung Kang, Hee Jin Jung, Sultan Ullah, Jieun Lee, Yeongmu Jeong, Sang Gyun Noh, Dongwan Kang, Yujin Park, Pusoon Chun, Hae Young Chung and Hyung Ryong Moon

Molecules 2023, 28(8), 3293; https://doi.org/10.3390/molecules28083293 - 7 Apr 2023

Cited by 3 | Viewed by 1829

Abstract

(Z)-5-Benzylidene-2-phenylthiazol-4(5H)-one ((Z)-BPT) derivatives were designed by combining the structural characteristics of two tyrosinase inhibitors. The double-bond geometry of trisubstituted alkenes, (Z)-BPTs 1–14, was determined based on the ³J_C,Hβ coupling constant of ¹H-coupled ¹³C NMR spectra. Three (Z)-BPT derivatives (1–3) showed stronger tyrosinase inhibitory activities than kojic acid; in particular, 2 was to be 189-fold more potent than kojic acid. Kinetic analysis using mushroom tyrosinase indicated that 1 and 2 were competitive inhibitors, whereas 3 was a mixed-type inhibitor. The in silico results revealed that 1–3 could strongly bind to the active sites of mushroom and human tyrosinases, supporting the kinetic results. Derivatives 1 and 2 decreased the intracellular melanin contents in a concentration-dependent manner in B16F10 cells, and their anti-melanogenic efficacy exceeded that of kojic acid. The anti-tyrosinase activity of 1 and 2 in B16F10 cells was similar to their anti-melanogenic effects, suggesting that their anti-melanogenic effects were primarily owing to their anti-tyrosinase activity. Western blotting of B16F10 cells revealed that the derivatives 1 and 2 inhibited tyrosinase expression, which partially contributes to their anti-melanogenic ability. Several derivatives, including 2 and 3, exhibited potent antioxidant activities against ABTS cation radicals, DPPH radicals, ROS, and peroxynitrite. These results suggest that (Z)-BPT derivatives 1 and 2 have promising potential as novel anti-melanogenic agents. Full article

(This article belongs to the Special Issue Advances in Synthesis and Biological Activity of Novel Derivatives Based on Five-Membered Heterocyclic Scaffolds and Their Intermediates)

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15 pages, 2756 KiB

Open AccessArticle

Novel 1,2,3-Triazole-Based Benzothiazole Derivatives: Efficient Synthesis, DFT, Molecular Docking, and ADMET Studies

by Zohreh Mirjafary, Mahdieh Mohammad Karbasi, Parsa Hesamzadeh, Hamid Reza Shaker, Asghar Amiri and Hamid Saeidian

Molecules 2022, 27(23), 8555; https://doi.org/10.3390/molecules27238555 - 5 Dec 2022

Cited by 9 | Viewed by 2686

Abstract

A new series of 1,2,3-triazole derivatives 5a–f based on benzothiazole were synthesized by the 1,3-dipolar cycloaddition reaction of S-propargyl mercaptobenzothiazole and α-halo ester/amide in moderate to good yields (47–75%). The structure of all products was characterized by ¹H NMR, ¹³C NMR, and CHN elemental data. This protocol is easy and green and proceeds under mild and green reaction conditions with available starting materials. The structural and electronic analysis and ¹H and ¹³C chemical shifts of the characterized structure of 5e were also calculated by applying the B3LYP/6-31 + G(d, p) level of density functional theory (DFT) method. In the final section, all the synthesized compounds were evaluated for their anti-inflammatory activity by biochemical COX-2 inhibition, antifungal inhibition with CYP51, anti-tuberculosis target protein ENR, DPRE1, pks13, and Thymidylate kinase by molecular docking studies. The ADMET analysis of the molecules 5a–f revealed that 5d and 5a are the most-promising drug-like molecules out of the six synthesized molecules. Full article

(This article belongs to the Special Issue Advances in Synthesis and Biological Activity of Novel Derivatives Based on Five-Membered Heterocyclic Scaffolds and Their Intermediates)

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15 pages, 1629 KiB

Open AccessArticle

Green and Efficient Construction of Chromeno[3,4-c]pyrrole Core via Barton–Zard Reaction from 3-Nitro-2H-chromenes and Ethyl Isocyanoacetate

by Ivan A. Kochnev, Alexey Y. Barkov, Nikolay S. Zimnitskiy, Vladislav Y. Korotaev and Vyacheslav Y. Sosnovskikh

Molecules 2022, 27(23), 8456; https://doi.org/10.3390/molecules27238456 - 2 Dec 2022

Cited by 4 | Viewed by 1847

Abstract

A regioselective one-pot method for the synthesis of 1-ethyl 2,4-dihydrochromene[3,4-c]pyrroles in 63–94% yields from available 2-phenyl-, 2-trifluoro(trichloro)methyl- or 2-phenyl-2-(trifluoromethyl)-3-nitro-2H-chromenes and ethyl isocyanoacetate through the Barton–Zard reaction in ethanol at reflux for 0.5 h, using K₂CO₃ as a base, has been developed. Full article

(This article belongs to the Special Issue Advances in Synthesis and Biological Activity of Novel Derivatives Based on Five-Membered Heterocyclic Scaffolds and Their Intermediates)

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12 pages, 3235 KiB

Open AccessArticle

Silver-Catalyzed Cascade Cyclization of Amino-NH-1,2,3-Triazoles with 2-Alkynylbenzaldehydes: An Access to Pentacyclic Fused Triazoles

by Shuitao Zhang, Jianxin Li, Tiebo Xiao, Baomin Yang and Yubo Jiang

Molecules 2022, 27(21), 7567; https://doi.org/10.3390/molecules27217567 - 4 Nov 2022

Cited by 5 | Viewed by 1818

Abstract

An operationally simple Ag(I)-catalyzed approach for the synthesis of isoquinoline and quinazoline fused 1,2,3-triazoles was developed by a condensation and amination cyclization cascade of amino-NH-1,2,3-triazoles with 2-alkynylbenzaldehydes involving three new C-N bond formations in one manipulation, in which the group of -NH of the triazole ring serves as a nucleophile to form the quinazoline skeleton. The efficient protocol can be applied to a variety of substrates containing a range of functional groups, delivering novel pentacyclic fused 1,2,3-triazoles in good-to-excellent yields. Full article

(This article belongs to the Special Issue Advances in Synthesis and Biological Activity of Novel Derivatives Based on Five-Membered Heterocyclic Scaffolds and Their Intermediates)

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Review

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36 pages, 10158 KiB

Open AccessReview

Significance of Five-Membered Heterocycles in Human Histone Deacetylase Inhibitors

by Anton Frühauf, Martin Behringer and Franz-Josef Meyer-Almes

Molecules 2023, 28(15), 5686; https://doi.org/10.3390/molecules28155686 - 27 Jul 2023

Cited by 7 | Viewed by 2594

Abstract

Five-membered heteroaromatic rings, in particular, have gained prominence in medicinal chemistry as they offer enhanced metabolic stability, solubility and bioavailability, crucial factors in developing effective drugs. The unique physicochemical properties and biological effects of five-membered heterocycles have positioned them as key structural motifs in numerous clinically effective drugs. Hence, the exploration of five-ring heterocycles remains an important research area in medicinal chemistry, with the aim of discovering new therapeutic agents for various diseases. This review addresses the incorporation of heteroatoms such as nitrogen, oxygen and sulfur into the aromatic ring of these heterocyclic compounds, enhancing their polarity and facilitating both aromatic stacking interactions and the formation of hydrogen bonds. Histone deacetylases are present in numerous multiprotein complexes within the epigenetic machinery and play a central role in various cellular processes. They have emerged as important targets for cancer, neurodegenerative diseases and other therapeutic indications. In histone deacetylase inhibitors (HDACi’s), five-ring heterocycles perform various functions as a zinc-binding group, a linker or head group, contributing to binding activity and selective recognition. This review focuses on providing an up-to-date overview of the different five-membered heterocycles utilized in HDACi motifs, highlighting their biological properties. It summarizes relevant publications from the past decade, offering insights into the recent advancements in this field of research. Full article

(This article belongs to the Special Issue Advances in Synthesis and Biological Activity of Novel Derivatives Based on Five-Membered Heterocyclic Scaffolds and Their Intermediates)

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23 pages, 6467 KiB

Open AccessReview

A Survey on the Synthesis of Variolins, Meridianins, and Meriolins—Naturally Occurring Marine (aza)Indole Alkaloids and Their Semisynthetic Derivatives

by Marco Kruppa and Thomas J. J. Müller

Molecules 2023, 28(3), 947; https://doi.org/10.3390/molecules28030947 - 18 Jan 2023

Cited by 5 | Viewed by 2187

Abstract

Marine natural products are a source of essential significance due to a plethora of highly diverse biological properties. The naturally occurring (aza)indole alkaloids variolin B (1), meridianins (2), and their synthetic hybrids meriolins (3) exhibit potent kinase inhibitory activities and have aroused considerable interest in the past two decades. Therefore, the immense demand for versatile synthetic accesses to these structures has considerably increased. This review surveys the synthetic pathways to these naturally occurring alkaloids and their semisynthetic derivatives. Full article

(This article belongs to the Special Issue Advances in Synthesis and Biological Activity of Novel Derivatives Based on Five-Membered Heterocyclic Scaffolds and Their Intermediates)

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19 pages, 2145 KiB

Open AccessReview

Recent Advances on Small-Molecule Antagonists Targeting TLR7

by Haoyang Zheng, Peiyang Wu and Pierre-Antoine Bonnet

Molecules 2023, 28(2), 634; https://doi.org/10.3390/molecules28020634 - 7 Jan 2023

Cited by 10 | Viewed by 5366

Abstract

Toll-like receptor 7 (TLR7) is a class of pattern recognition receptors (PRRs) recognizing the pathogen-associated elements and damage and as such is a major player in the innate immune system. TLR7 triggers the release of pro-inflammatory cytokines or type-I interferons (IFN), which is essential for immunoregulation. Increasing reports also highlight that the abnormal activation of endosomal TLR7 is implicated in various immune-related diseases, carcinogenesis as well as the proliferation of human immunodeficiency virus (HIV). Hence, the design and development of potent and selective TLR7 antagonists based on small molecules or oligonucleotides may offer new tools for the prevention and management of such diseases. In this review, we offer an updated overview of the main structural features and therapeutic potential of small-molecule antagonists of TLR7. Various heterocyclic scaffolds targeting TLR7 binding sites are presented: pyrazoloquinoxaline, quinazoline, purine, imidazopyridine, pyridone, benzanilide, pyrazolopyrimidine/pyridine, benzoxazole, indazole, indole, and quinoline. Additionally, their structure-activity relationships (SAR) studies associated with biological activities and protein binding modes are introduced. Full article

(This article belongs to the Special Issue Advances in Synthesis and Biological Activity of Novel Derivatives Based on Five-Membered Heterocyclic Scaffolds and Their Intermediates)

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38 pages, 17273 KiB

Open AccessReview

Acylhydrazones and Their Biological Activity: A Review

by Laura-Ileana Socea, Stefania-Felicia Barbuceanu, Elena Mihaela Pahontu, Alexandru-Claudiu Dumitru, George Mihai Nitulescu, Roxana Corina Sfetea and Theodora-Venera Apostol

Molecules 2022, 27(24), 8719; https://doi.org/10.3390/molecules27248719 - 9 Dec 2022

Cited by 36 | Viewed by 5245

Abstract

Due to the structure of acylhydrazones both by the pharmacophore –CO–NH–N= group and by the different substituents present in the molecules of compounds of this class, various pharmacological activities were reported, including antitumor, antimicrobial, antiviral, antiparasitic, anti-inflammatory, immunomodulatory, antiedematous, antiglaucomatous, antidiabetic, antioxidant, and actions on the central nervous system and on the cardiovascular system. This fragment is found in the structure of several drugs used in the therapy of some diseases that are at the top of public health problems, like microbial infections and cardiovascular diseases. Moreover, the acylhydrazone moiety is present in the structure of some compounds with possible applications in the treatment of other different pathologies, such as schizophrenia, Parkinson’s disease, Alzheimer’s disease, and Huntington’s disease. Considering these aspects, we consider that a study of the literature data regarding the structural and biological properties of these compounds is useful. Full article

(This article belongs to the Special Issue Advances in Synthesis and Biological Activity of Novel Derivatives Based on Five-Membered Heterocyclic Scaffolds and Their Intermediates)

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