Recent Advances in the Synthesis of Spiro‐β‐Lactams and Spiro‐δ‐Lactams

Synthesis, identification and evaluation of molecular docking and experimental anti-cancer and antioxidant activity of new spiro four membered ring derivatives bearing 5-nitro isatin

Spiro-5-nitro isatino aza-β-lactams were produced by a [2 + 2] cycloaddition of 5-nitro isatin Schiff bases [1-5] with different aromatic isocyanate and thioisocyanate. 1HNMR and 13CNMR as well as FTIR spectroscopies, were used to identify the structures of the obtained compounds. These spiro-5-nitro isatin aza- β-lactams interest to us due to their potential antioxidant and anticancer properties. The MTT assay was used to examine in vitro bioactivity testing against breast cancer (MCF-7) cell lines. From result data, compound 14 displayed IC50 values that were lower than those of the clinically used anticancer drug tamoxifen toward MCF-7 cells after 24 h while compound 9 after 48 h synthesized compounds [6-20] were evaluated for against antioxidant activity by using DPPH assay. In molecular docking, Promising compounds were used to reveal potential cytotoxic activity mechanisms.

Copper-Catalyzed Asymmetric Kinugasa/Michael Addition Cascade Reactions for the Synthesis of Chiral Spiro β-Lactams

A mild copper-catalyzed asymmetric Kinugasa/Michael addition cascade process is developed. The reaction of α, β-unsaturated ester-tethered propiolamides with nitrones provides an efficient protocol for the construction of functionalized chiral 2,6-diazaspiro[3.4]octane-1,5-dione products in satisfactory yields and with high enantio- and diastereoselectivities.

Stereodivergent Synthesis of All Stereoisomers of 2,3-Disubstituted δ-Lactam Derivatives via Organocatalytic Cascade Reactions and Base-Induced Epimerization

A protocol was developed to achieve stereodivergent synthesis of stereoisomers of δ-lactam bearing vicinal chiral centers. Organocatalytic cascade reactions were employed to produce the target products as the kinetic products, which exhibited remarkable enantioselectivities. In the presence of DBU, the kinetic product underwent epimerization to form a thermodynamically more stable diastereomer without loss in enantioselectivity. By simply switching the chiral organocatalyst and its enantiomer, we can efficiently obtain four stereoisomers with high enantioselectivities.

Cooperative Chiral Lewis Base/Palladium-Catalyzed Asymmetric Syntheses of Methylene-Containing δ-Lactams

We herein report a two-step approach for the enantioselective synthesis of novel chiral δ-lactams. By using a cooperative chiral ITU/achiral Pd-catalyst system, this protocol proceeds via an asymmetric α-allylation of activated aryl esters first, followed by an acid-mediated lactam formation. A variety of differently substituted products could be obtained with usually high levels of enantioselectivities and in reasonable yields (16 examples, up to 98 : 2 er and 73 % yield over two steps). In addition, further utilizations of the products via transformations of the exocyclic double bond were successfully carried out as well.

Recent synthetic strategies of spiro-azetidin-2-one, -pyrrolidine, -indol(one) and -pyran derivatives-a review

Spiro-heterocycles have received special attention in medicinal chemistry because of their promising biological activity. Over the years, many synthetic methodologies have been established for the construction of spirocyclic compounds. Spiro heterocycles such as spiro-azetidin-2-one, -pyrrolidine, -indol(one) and -pyran derivatives have been found to exhibit diversified biological and pharmacological activity in addition to their therapeutic properties. In view of these facts, we decided in this review to present representative synthetic approaches of the aforementioned spiro heterocycles, especially in the past 20 years.

Modular Synthesis of Polar Spirocyclic Scaffolds Enabled by Radical Chemistry

Herein, we report a highly modular strategy to access spirocyclic scaffolds from abundant starting materials, i.e., cyclic ketones and α-amino or oxamic acids. The sequence proceeds through a straightforward Knoevenagel condensation, followed by a domino Giese-type reaction/base-mediated cyclization process, to deliver a broad scope of polar spirocyclic scaffolds in good to excellent yields. The products can be readily diversified, thus increasing the versatility of our method to gain rapid access to libraries of potential druglike molecules.

Cis-Selective Double Spirocyclization via Dearomatization and Isomerization under Thermodynamic Control

Spiro compounds have been considered key scaffolds for pharmaceutical applications. Although many synthetic methods exist for monospirocycles, fewer approaches are known for dispirocycles. Here, we report a highly cis-selective method for constructing a 5/6/5-dispirocyclic structure containing pyrrolidine and γ-lactam rings with various substituents from a series of N-arylpropiolamides. The high cis-selectivity would result from isomerization under thermodynamic control. Cis- and trans-diastereomers can be in equilibrium, favoring cis-adducts.

Unveiling a family of spiro-β-lactams with anti-HIV and antiplasmodial activity via phosphine-catalyzed [3+2] annulation of 6-alkylidene-penicillanates and allenoates

The molecular architecture of spirocyclic compounds has been widely explored within the medicinal chemistry field to obtain new compounds with singular three-dimensional pharmacophoric features and improved bioactivity. Herein, the synthesis of 68 new spirocyclopentene-β-lactams is described, resulting from a rational drug design and structural modulation of a highly promising lead compound BSS-730A, previously identified as having dual antimicrobial activity associated with a novel mechanism of action. Among this diverse library of new compounds, 22 were identified as active against HIV-1, with eight displaying an IC₅₀ lower than 50 nM. These eight compounds also showed nanomolar activity against HIV-2, and six of them displayed micromolar antiplasmodial activity against both the hepatic and the blood stages of infection by malaria parasites, in agreement with the lead molecule’s bioactivity profile. The spirocyclopentene-β-lactams screened also showed low cytotoxicity against TZM-bl and Huh7 human cell lines. Overall, a family of new spirocyclopentene penicillanates with potent activity against HIV and/or Plasmodium was identified. The present structure–activity relationship open avenues for further development of spirocyclopentene-β-lactams as multivalent, highly active broad spectrum antimicrobial agents.

Multicomponent Direct Assembly of N-Heterospirocycles Facilitated by Visible-Light-Driven Photocatalysis

N-heterospirocycles are interesting structural units found in both natural products and medicinal compounds but have relatively few reliable methods for their synthesis. Here, we enlist the photocatalytic generation of N-centered radicals to construct β-spirocyclic pyrrolidines from N-allylsulfonamides and alkenes. A variety of β-spirocyclic pyrrolidines have been constructed, including drug derivatives, in moderate to very good yields. Further derivatization of the products has also been demonstrated as has a viable scale-up procedure, making use of flow chemistry techniques.

Palladium-Catalyzed Access to Benzocyclobutenone-Derived Ketonitrones via C(sp2)-H Functionalization

The palladium-catalyzed C(sp²)–H functionalization of bromoaryl aldonitrones leading to benzocyclobutenone-derived ketonitrones is described. This method allows for the preparation of a wide range of strained, four-membered ketonitrones with broad functional group tolerance. Downstream transformations of the formed products were readily demonstrated, illustrating the synthetic utility of the obtained benzocyclobutenone-derived nitrones for the construction of polycyclic nitrogen-containing scaffolds.

Visible Light-Mediated Dearomative Hydrogen Atom Abstraction/ Cyclization Cascade of Indoles

The photochemical synthesis of yet unknown 2‐oxospiro[azetidine‐3,3′‐indolines] (17 examples, 80–95 % yield), 2,4‐dioxospiro[azetidine‐3,3′‐indolines] (eight examples, 87–97 % yield), and 1‐oxo‐1,3‐dihydrospiro[indene‐2,3′‐indolines] (17 examples, 85–97 % yield) is described. Starting from readily accessible 3‐substituted indoles, a dearomatization of the indole core was accomplished upon irradiation at λ=420 nm in the presence of thioxanthen‐9‐one (10 mol%) as the sensitizer. Based on mechanistic evidence (triplet energy determination, deuteration experiments, by‐product analysis) it is proposed that the reaction proceeds by energy transfer via a 1,4‐ or 1,5‐diradical intermediate. The latter intermediates are formed by excited state hydrogen atom transfer from suitable alkyl groups within the C3 substituent to the indole C2 carbon atom. Subsequent ring closure proceeds with pronounced diastereoselectivity to generate a 4‐ or 5‐membered spirocyclic dearomatized product with several options for further functionalization.

Bromo-lactamization of isoxazole via neighboring group participation: toward spiro-isoxazoline γ- and δ-lactams

Spiro-heterocycles containing natural products and synthetic analogues have a broader biomedicinal application due to their rigid 3D conformation and structural implications. In this context, constructing spiro-isoxazoline systems have continued our interest in natural products and synthetic units to investigate their novel biological activities. Herein, a bromo-lactamization mediated neighboring group participation approach has been utilized on various isoxazole-amides to construct an array of spiro-isoxazoline-lactams. The easy synthesis with diverse functionalization in the periphery of a novel 3D framework could be interesting for biomedical investigation.

Visible-Light-Mediated Sequential Wolff Rearrangement and Staudinger Cycloaddition Enabling Assembly of Spiro-Pyrazolone-β-Lactams

Visible-light-mediated sequential Wolff rearrangement and Staudinger cycloaddition for the assembly of valuable spiro-pyrazolone-β-lactams for the first time is disclosed by utilizing in situ generated ketenes and pyrazolone ketimines. This powerful...

Synthesis of novel chiral spiro-β-lactams from nitrile oxides and 6-(Z)-(benzoylmethylene)penicillanate: batch, microwave-induced and continuous flow methodologies

The first examples of the diastereoselective 1,3-dipolar cycloaddition reaction of nitrile oxides and 6-alkylidene penicillanates leading to chiral spiroisoxazoline-penicillanates are reported. The synthesis of this new type of penicillanate involved the selective generation of two consecutive stereogenic centers, including a quaternary chiral center. Furthermore, the present work also describes the outcomes of these 1,3-dipolar cycloaddition reactions under three distinct reaction conditions (conventional heating, microwave irradiation and continuous flow). The successful use of the continuous flow technique as well as the proper selection of the reaction media allowed the development of a sustainable route to chiral spiroisoxazoline-penicillanates.

The first examples of the diastereoselective 1,3-dipolar cycloaddition reaction of nitrile oxides and 6-alkylidene penicillanates leading to chiral spiroisoxazoline-penicillanates are reported.

Application of chiral triazole-substituted iodoarenes in the enantioselective construction of spirooxazolines

A catalytic highly enantioselective synthesis of spirooxazolines is presented. Starting from readily available 2-naphthol-substituted benzamides and using catalytic amounts of a chiral triazole-substituted iodoarene catalyst, a variety of spirooxazolines can be isolated through an enantioselective oxidative dearomatization in up to 92% yield and 97% ee. The further synthetic utility of the optically enriched spirooxazolines was examined providing a corresponding 2-naphthalenole and an oxepin.

Unmasking the reverse reactivity of cyclic N-sulfonyl ketimines: multifaceted applications in organic synthesis

The chemistry related to the exploration of cyclic N-sulfonyl ketimines and their derivatives has attracted significant attention in the last few decades because of their intriguing structures and properties. They serve broadly as reactive synthons in various reactions to create a diverse set of synthetically and biologically attractive molecules. Furthermore, these moieties, which possess multiple heteroatoms (N, O and S), display or can enhance many biological activities. In the case of synthetic reactions, chemists mainly focus on the chemical manipulation of the highly reactive prochiral CN bond of N-sulfonyl ketimines. Besides their traditional role as electrophiles, N-sulfonyl ketimines possess α-Csp³-H protons, and thus behave as potential carbonucleophiles, where they can undergo several C-X (X = C, N and O) bond-forming reactions with different types of electrophiles under various conditions to form a wide range of fascinating asymmetric and non-asymmetric versions of fused heterocycles, carbocycles, spiro-fused skeletons, pyridines, pyrroles, etc. Herein, we highlight the recent examples from our research work and others covering the scope of cyclic N-sulfonyl ketimines as useful carbonucleophiles. In addition, the detailed mechanistic studies of the above-mentioned reactions are also presented.