Synthesis, structural elucidation and in vitro antiparasitic activity against Trypanosoma cruzi and Leishmania chagasi parasites of novel tetrahydro-1-benzazepine derivatives

Synthesis of 1,4-epoxy-2-aryltetrahydro-1-benzazepines via rhodium(III)-catalyzed C-H allylation/intramolecular 1,3-dipolar cycloaddition

Herein, we report a new synthetic route to 1,4-epoxy-2-aryltetrahydro-1-benzazepine derivatives with high efficiency, namely the Rh(III)-catalyzed C-H allylation of nitrones with allyl precursors, followed by subsequent intramolecular 1,3-dipolar cycloaddition, to deliver the title compounds. This reaction is regio- and stereo-selective, generating the cis-isomer with a broad substrate scope and good functional group tolerance.

I2-Mediated [6 + 1] Annulation of Alkynes with MsONH3OTf: Direct Synthesis of Benzo[b]azepines

The synthesis of benzo[b]azepines using protonated aminating reagent (MsONH₃OTf) and alkynes through I₂-mediated [6 + 1] annulation reaction has been developed. This protocol features excellent functional group tolerance and mild reaction conditions and affords the benzo[b]azepines in moderate to good yields under metal-free reaction conditions.

A palladium-catalyzed ring-expansion reaction of cyclobutanols with 2-haloanilines leading to benzazepines and quinolines

A general synthesis of 2-aryl benzazepines has been developed through palladium-catalyzed ring-expansion reactions of cyclobutanols with 2-haloanilines; the further oxidative rearrangement reaction of benzazepines provided an efficient synthesis of 2-acyl quinolines. These transformations feature the efficient construction of six- and seven-membered N-containing heterocycles from easily obtained materials with excellent functional group tolerance.

I2 -Promoted Intramolecular Oxidative Cyclization of Butenyl Anilines: A Facile Route to Benzo[b]azepines

A metal-free approach for the synthesis of seven-membered N-heterocycles has been developed by the I₂ -promoted intramolecular cross-coupling/annulation of butenyl anilines. This cyclization reaction involves C-H activation and C-C bond formation and exhibits good functional group tolerance. A series of benzo[b]azepine derivatives are obtained in moderate to good yields.

Reaction of Vinyl Aziridines with Arynes: Synthesis of Benzazepines and Branched Allyl Fluorides

We report the cycloaddition between vinyl aziridines and arynes. Depending on the reaction conditions and the choice of the aryne precursor, the aziridinium intermediate can be trapped through two distinct mechanistic pathways. The first one proceeds through a formal [5+2] cycloaddition to furnish valuable multi-substituted benzazepines. In the second pathway, the aziridinium is intercepted by a fluoride ion to afford allylic fluorides in good yields. Both reactions proceed stereospecifically and furnish enantiopure benzazepines and allylic fluorides.

PIII-Mediated intramolecular cyclopropanation and metal-free synthesis of cyclopropane-fused heterocycles

The carbene-like reactivity of the Kukhtin–Ramirez adduct enables the first reductive intramolecular cyclopropanation, which provides easy access to highly functionalized cyclopropane-fused heterocycles.

Mild, Metal-Free Oxidative Ring-Expansion Approach for the Synthesis of Benzo[ b]azepines

Benzo[ b]azepines are important structural motifs for the pharmaceutical industry. However, their syntheses are usually lengthy, involving several steps, transition-metal catalysts, and/or harsh conditions. A novel, general, mild, and metal-free oxidative ring expansion tandem reaction of hydroquinolines with TMSCHN₂ as a versatile soft nucleophile to gain access to these valuable compounds in a simple and straightforward manner is presented.

Quantitative Structure-Activity Relationships for Structurally Diverse Chemotypes Having Anti-Trypanosoma cruzi Activity

Small-molecule compounds that have promising activity against macromolecular targets from Trypanosoma cruzi occasionally fail when tested in whole-cell phenotypic assays. This outcome can be attributed to many factors, including inadequate physicochemical and pharmacokinetic properties. Unsuitable physicochemical profiles usually result in molecules with a poor ability to cross cell membranes. Quantitative structure-activity relationship (QSAR) analysis is a valuable approach to the investigation of how physicochemical characteristics affect biological activity. In this study, artificial neural networks (ANNs) and kernel-based partial least squares regression (KPLS) were developed using anti-T. cruzi activity data for broadly diverse chemotypes. The models exhibited a good predictive ability for the test set compounds, yielding q² values of 0.81 and 0.84 for the ANN and KPLS models, respectively. The results of this investigation highlighted privileged molecular scaffolds and the optimum physicochemical space associated with high anti-T. cruzi activity, which provided important guidelines for the design of novel trypanocidal agents having drug-like properties.

A concise and versatile route to tetrahydro-1-benzazepines carrying [a]-fused heterocyclic units: synthetic sequence and spectroscopic characterization, and the molecular and supramolecular structures of one intermediate and two products

A concise, efficient and versatile route from simple starting materials to tricyclic tetrahydro-1-benzazepines carrying [a]-fused heterocyclic units is reported. Thus, the easily accessible methyl 2-[(2-allyl-4-chlorophenyl)amino]acetate, (I), was converted, via (2RS,4SR)-7-chloro-2,3,4,5-tetrahydro-1,4-epoxy-1-benzo[b]azepine-2-carboxylate, (II), to the key intermediate methyl (2RS,4SR)-7-chloro-4-hydroxy-2,3,4,5-tetrahydro-1H-benzo[b]azepine-2-carboxylate, (III). Chloroacetylation of (III) provided the two regioisomers methyl (2RS,4SR)-7-chloro-1-(2-chloroacetyl)-4-hydroxy-2,3,4,5-tetrahydro-1H-benzo[b]azepine-2-carboxylate, (IVa), and methyl (2RS,4SR)-7-chloro-4-(2-chloroacetoxy)-2,3,4,5-tetrahydro-1H-benzo[b]azepine-2-carboxylate, C₁₄H₁₅Cl₂NO₄, (IVb), as the major and minor products, respectively, and further reaction of (IVa) with aminoethanol gave the tricyclic target compound (4aRS,6SR)-9-chloro-6-hydroxy-3-(2-hydroxyethyl)-2,3,4a,5,6,7-hexahydrobenzo[f]pyrazino[1,2-a]azepine-1,4-dione, C₁₅H₁₇ClN₂O₄, (V). Reaction of ester (III) with hydrazine hydrate gave the corresponding carbohydrazide (VI), which, with trimethoxymethane, gave a second tricyclic target product, (4aRS,6SR)-9-chloro-6-hydroxy-4a,5,6,7-tetrahydrobenzo[f][1,2,4]triazino[4,5-a]azepin-4(3H)-one, C₁₂H₁₂ClN₃O₂, (VII). Full spectroscopic characterization (IR, ¹H and ¹³C NMR, and mass spectrometry) is reported for each of compounds (I)-(III), (IVa), (IVb) and (V)-(VII), along with the molecular and supramolecular structures of (IVb), (V) and (VII). In each of (IVb), (V) and (VII), the azepine ring adopts a chair conformation and the six-membered heterocyclic rings in (V) and (VII) adopt approximate boat forms. The molecules in (IVb), (V) and (VII) are linked, in each case, into complex hydrogen-bonded sheets, but these sheets all contain a different range of hydrogen-bond types: N-H...O, C-H...O, C-H...N and C-H...π(arene) in (IVb), multiple C-H...O hydrogen bonds in (V), and N-H...N, O-H...O, C-H...N, C-H...O and C-H...π(arene) in (VII).

Gold-catalyzed (4+3)-annulations of 2-alkenyl-1-alkynylbenzenes with anthranils with alkyne-dependent chemoselectivity: skeletal rearrangement versus non-rearrangement

Two distinct (4+3)-nitroxy annulations between 1,5-enynes and anthranils have been developed to access tetrahydro-1H-benzo[b]azepine derivatives.

Two distinct (4+3)-nitroxy annulations between 1,5-enynes and anthranils have been developed to access tetrahydro-1H-benzo[b]azepine derivatives; the chemoselectivity varies with the types of alkynes. Terminal alkyne substrates deliver benzo[b]azepine derivatives via a novel skeletal rearrangement while internal 1,5-enynes afford products without a rearrangement process. To elucidate the mechanism of rearrangement, we performed ¹³C- and ²H-labeling experiments to identify the gold-containing isobenzofulvene intermediates, but their formation relies on the presence of anthranils.

Lewis acid catalyzed diastereoselective [3+4]-annulation of donor–acceptor cyclopropanes with anthranils: synthesis of tetrahydro-1-benzazepine derivatives

The [3+4]-annulation between donor–acceptor cyclopropanes and anthranils has been developed for the diastereoselective synthesis of tetrahydro-1-benzazepine derivatives.

Synthesis of Xylitan Derivatives and Preliminary Evaluation of in Vitro Trypanocidal Activity

A series of novel xylitan derivatives derived from xylitol were synthesized using operationally simple procedures. A xylitan acetonide was the key intermediate used to prepare benzoate, arylsulfonate esters and 1,2,3-triazole derivatives of xylitan. These compounds were evaluated for their in vitro anti-Trypanosoma cruzi activity against trypomastigote and amastigote forms of the parasite in T. cruzi-infected cell lineages. Benznidazole was used as positive control against T. cruzi and cytotoxicity was determined in mammalian L929 cells. The arylsulfonate xylitan derivative bearing a nitro group displayed the best activity of all the compounds tested, and was slightly more potent than the reference drug benznidazole. The importance of the isopropylidene ketal moiety was established and the greater lipophilicity of these compounds suggests enhancement in cell penetration.

The alkylphospholipid edelfosine shows activity against Strongyloides venezuelensis and induces apoptosis-like cell death

Strongyloidiasis is widely distributed in the tropical and subtropical areas. Ivermectin is the drug of choice for the treatment. However, the concerns about relying treatment on a single drug make identification of new molecules a priority. Alkylphospholipid analogues, including edelfosine, are a group of synthetic compounds that have shown activity against some parasites. The objective was to assess the in vitro and in vivo activity of edelfosine, miltefosine, perifosine against Strongyloides venezuelensis. Moreover, apoptosis-like mechanism in larvae after treatment was studied. Edelfosine displayed the highest activity and the best selectivity index (LD50=49.6 ± 5.4μM, SI=1.1) compared to miltefosine or perifosine. Third stage larvae after culture with edelfosine were not able to develop an infection in mice. Treatment of mice with edelfosine showed reduction of 47% in parasitic females allocated in the gut. Moreover, DNA fragmentation was observed by TUNEL staining in larvae treated with edelfosine. These results suggest that edelfosine could be an effective drug against strongyloidiasis, probably through induction of apoptosis-like cell death.

In vitro and in vivo evaluation of 2-aminoalkanol and 1,2-alkanediamine derivatives against Strongyloides venezuelensis

Background

Strongyloidiasis is a parasitic disease widely present in tropical and subtropical areas. Strongyloides stercoralis represents the main species that infects human beings. Ivermectin is the current drug of choice; however, issues related with treatment failure in patients with diabetes or infected with T-lymphotropic virus-1 make the identification of new molecules for alternative treatment a priority. In the present study, the activity of sphingosine-related aminoalcohol and diamine were evaluated against Strongyloides venezuelensis third-stage larva (L3) cultures and experimental infections in mice.

Methods

The efficacy of each compound against L3 was assessed using both XTT (2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide) assay and microscopic observation with concentrations ranging from 1 to 350 μM. Cytotoxicity was evaluated using J774.2 macrophage cell line and XTT assay. Lethal concentration 50 (LC₅₀), selectivity index (SI) and structure-activity relationships were established. The activity compounds 4 (2-(ethylamino) hexadecan-1-ol), 6 (2-(butylamino) hexadecan-1-ol), 17 (tert-butyl N-(1-aminododecan-2-yl) carbamate) and 18 (tert-butyl N-(1-aminohexadecan-2-yl) carbamate) were further assessed against experimental S. venezuelensis infections in CD1 mice measuring reductions in the numbers of parthenogenetic females and egg passed in faeces. Mice were infected with 3,000 L3 and treated with 20 mg/kg/day for five days.

Results

In the screening study of 15 aminoalcohols [lauryl (n = 9); palmityl (n = 13); stearyl (n = 15) and alcohol derivatives], the presence of a palmitol chain was associated with the highest efficacy against L3 (LC₅₀ 31.9–39.1 μM). Alkylation of the 2-amino group with medium size fragments as ethyl or n-butyl showed the best larvicidal activity. The dialkylation did not improve efficacy. Aminoalcohols 4 and 6 showed the highest SI (1.5 and 1.6, respectively). With respect to diamine derivative compounds, a chain size of sixteen carbon atoms (palmitoyl chain, n = 13), and the alkylation of the 2-amino group with medium-sized fragments, were associated with the highest lethal activities. The presence of carbamoyl group in diamines 17 and 18 yielded high SI (1.7 and 1.4, respectively). Infected mice treated with aminoalcohol 6 showed reduction in parthenogenetic females (59 %) and eggs in faeces (51 %).

Conclusions

These results support the potentiality of aminoalcohol and diamine sphingosine-related compounds as suitable prototypes for developing new promising drugs against strongyloidiasis.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-016-1648-5) contains supplementary material, which is available to authorized users.

Crystal structures of five new substituted tetrahydro-1-benzazepines with potential antiparasitic activity

Tetrahydro-1-benzazepines have been described as potential antiparasitic drugs for the treatment of chagas disease and leishmaniasis, two of the most important so-called `forgotten tropical diseases' affecting South and Central America, caused by Trypanosoma cruzi and Leishmania chagasi parasites, respectively. Continuing our extensive work describing the structural characteristics of some related compounds with interesting biological properties, the crystallographic features of three epoxy-1-benzazepines, namely (2SR,4RS)-6,8-dimethyl-2-(naphthalen-1-yl)-2,3,4,5-tetrahydro-1H-1,4-epoxy-1-benzazepine, (1), (2SR,4RS)-6,9-dimethyl-2-(naphthalen-1-yl)-2,3,4,5-tetrahydro-1H-1,4-epoxy-1-benzazepine, (2), and (2SR,4RS)-8,9-dimethyl-2-(naphthalen-1-yl)-2,3,4,5-tetrahydro-1H-1,4-epoxy-1-benzazepine, (3), all C22H21NO, and two 1-benzazepin-4-ols, namely 7-fluoro-cis-2-[(E)-styryl]-2,3,4,5-tetrahydro-1H-1-benzazepin-4-ol, C18H18FNO, (4), and 7-fluoro-cis-2-[(E)-pent-1-enyl]-2,3,4,5-tetrahydro-1H-1-benzazepin-4-ol, C15H20FNO, (5), are described. Some peculiarities in the crystallization behaviour were found, involving significant variations in the crystalline structures as a result of modest changes in the peripheral substituents in (1)-(3) and the occurrence of discrete disorder due to the molecular overlay of enantiomers with more than one conformation in (5). In particular, an interesting phase change on cooling was observed for compound (5), accompanied by an approximate fourfold increase of the unit-cell volume and a change of the Z' value from 1 to 4. This transition is a consequence of the partial ordering of the pentenyl chains in half of the molecules breaking half of the -3 symmetry axes observed in the room-temperature structure of (5). The structural assembly in all the title compounds is characterized by not only (N,O)-H...(O,N) hydrogen bonds, but also by unconventional C-H...O contacts, resulting in a wide diversity of packing.

Trypanocidal Activity of Long Chain Diamines and Aminoalcohols

Thirteen aminoalcohols and eight diamines were obtained and tested against Trypanosoma cruzi epimastigotes strains MG, JEM and CL-B5 clone. Some of them were equal or more potent (1.0–6.6 times) than the reference compound nifurtimox. From them, three aminoalcohols and two diamines were selected for amastigotes assays. Compound 5 was as potent as the reference drug nifurtimox against amastigotes of the CL-B5 strain (IC₅₀ = 0.6 µM), with a selectivity index of 54.

Synthesis of novel polysubstituted (2SR,4RS)-2-heteroaryltetrahydro-1,4-epoxy-1-benzazepines and cis-2-heteroaryl-4-hydroxytetrahydro-1H-1-benzazepines as antiparasitic agents

New series of polysubstituted (2SR,4RS)-2-heteroaryltetrahydro-1,4-epoxy-1-benzazepines and cis-2-heteroaryl-4-hydroxytetrahydro-1H-1-benzazepines were designed and synthesized in moderate to high yields using a three-step procedure from ortho-allylanilines. Their antiparasitic activity was evaluated against the extracellular and intracellular forms of Trypanosoma cruzi and Leishmania (Leishmania) infantum parasites. Their cytotoxicity was also determined on Vero and THP-1 mammalian cells. Many of the tested compounds inhibited significantly the growth of extracellular forms of T. cruzi and L. (L.) infantum without showing cytotoxicity on Vero and HTP-1 cells. Only compounds 10h and 14f demonstrated good activity against amastigotes of T. cruzi, but none was able to inhibit the growth of L. (L.) infantum amastigotes.

Four related benzazepine derivatives in a reaction pathway leading to a benzazepine carboxylic acid: hydrogen-bonded assembly in zero, one, two and three dimensions

(2R*,4S*)-Methyl 2,3,4,5-tetrahydro-1,4-epoxy-1H-benz[b]azepine-2-carboxylate, C12H13NO3, (I), and its reduction product (2R*,4S*)-methyl 4-hydroxy-2,3,4,5-tetrahydro-1H-benz[b]azepine-2-carboxylate, C12H15NO3, (II), both crystallize as single enantiomers in the space group P212121, while the hydrolysis product (2RS,4SR)-4-hydroxy-2,3,4,5-tetrahydro-1H-benz[b]azepine-2-carboxylic acid, C11H13NO3, (III), and the lactone (2RS,5SR)-8-(trifluoromethoxy)-5,6-dihydro-1H-2,5-methanobenz[e][1,4]oxazocin-3(2H)-one, C12H10F3NO3, (IV), both crystallize as racemic mixtures in the space group P21/c. The molecules of compound (IV) are linked into centrosymmetric R2(2)(10) dimers by N-H···O hydrogen bonds, and those of compound (I) are linked into chains by C-H···π(arene) hydrogen bonds. A combination of O-H···O and O-H···N hydrogen bonds links the molecules of compound (III) into sheets containing equal numbers of R4(4)(14) and R4(4)(26) rings, and a combination of C-H···π(arene) hydrogen bonds and three-centre O-H···(N,O) hydrogen bonds links the molecules of compound (II) into a three-dimensional framework structure. Comparisons are made with some related compounds.

In vitro antileishmanial, trypanocidal, and Mammalian cell activities of diverse n,n' -dihetaryl substituted diamines and related compounds

The leishmaniasis and Chagas diseases constitute a serious public health problem worldwide with few and ineffective treatment options. The search for new antiparasitic candidates at the initial steps of drug discovery and development is still necessary. The synthesis of 22 de novo synthetized N,N′-dihetaryl-alkyldiamine derivatives and in vitro antiparasitic activity were evaluated for the first time against intracellular and extracellular forms of Leishmania (Leishmania) infantum, L. (Viannia) panamensis, L. (Leishmania) amazonensis, and Trypanosoma cruzi. Additionally, the toxicity on mammalian cells was determined. Some of these substituted N,N′-diamines (25–35 % of the tested compounds) showed interesting results against free-living forms of parasites with activities at the inhibitory concentration (IC₅₀) level of 1.96 to 28.83 μM for L. (L.) infantum promastigotes and IC₅₀ of 0.02 to 5.31 μM for T. cruzi epimastigotes. No activity at the IC₅₀ level on intracellular amastigotes of T. cruzi was observed. However, N¹,N²-dibenzylethane-1,2-diamine 5a revealed an important activity against the intracellular amastigotes of L. infantum (IC₅₀ 25.42 μM ±0.33) and L. panamensis (IC₅₀ 58.20 μM ±3.23), while their analogue N¹,N⁴-dibenzylbutane-1,4-diamine 5c resulted in activity only against L. panamensis (IC₅₀ 11.19 μM ±0.20) without toxicity on Vero and THP-1 mammalian cells. The active compounds against intracellular parasites with low toxicity in mammalian cells may be considered for future studies in experimental models.

(2RS,4RS)-7-Fluoro-2-(2-phenylethyl)-2,3,4,5-tetrahydro-1H-1,4-epoxy-1-benzazepine and (2RS,4RS)-7-chloro-2-(2-phenylethyl)-2,3,4,5-tetrahydro-1H-1,4-epoxy-1-benzazepine are isomorphous but not strictly isostructural

(2RS,4RS)-7-Fluoro-2-(2-phenylethyl)-2,3,4,5-tetrahydro-1H-1,4-epoxy-1-benzazepine, C(18)H(18)FNO, (I), and (2RS,4RS)-7-chloro-2-(2-phenylethyl)-2,3,4,5-tetrahydro-1H-1,4-epoxy-1-benzazepine, C(18)H(18)ClNO, (II), are isomorphous but not strictly isostructural, as the slight differences in the unit-cell dimensions and molecular conformations are sufficient to preclude, in the structure of (I), the direction-specific intermolecular interactions present in the structure of (II), where the molecules are linked into sheets by a combination of C-H···N and C-H···π(arene) hydrogen bonds.

Chain formation by disordered, but correlated, hydrogen bonds in cis-(2RS,4SR)-2-(thiophen-2-yl)-2,3,4,5-tetrahydro-1H-1-benzazepin-4-ol and cis-(2RS,4SR)-2-(5-methylthiophen-2-yl)-2,3,4,5-tetrahydro-1H-1-benzazepin-4-ol

The closely related compounds cis-(2RS,4SR)-2-(thiophen-2-yl)-2,3,4,5-tetrahydro-1H-1-benzazepin-4-ol, C(14)H(15)NOS, (I), and cis-(2RS,4SR)-2-(5-methylthiophen-2-yl)-2,3,4,5-tetrahydro-1H-1-benzazepin-4-ol, C(15)H(17)NOS, (II), both crystallize with Z' = 2 in the space group P-1. In (I), the thienyl substituent in one of the two independent molecules is disordered over two sets of atomic sites having occupancies of 0.856 (2) and 0.144 (2). In both compounds, the two independent hydroxy O atoms are both within 2.8 Å of the hydroxy O atoms of two neighbouring molecules, and all of the hydroxy H atoms are disordered, each over two sites. The resulting O-H...O hydrogen bonds generate two similar but distinct C(4)(4)(8) chains, depending upon which hydroxy H-atom sites are occupied or vacant, with full correlation of the hydroxy H-atom occupancies within each chain. Comparisons are made with the supramolecular assembly in some related compounds.

Nine closely related tetrahydro-1,4-epoxy-1-benzazepines carrying pendant heterocyclic substituents: hydrogen-bonded supramolecular assembly in zero, one and two dimensions

The structures are reported of nine closely related tetrahydro-1,4-epoxy-1-benzazepines carrying pendant heterocyclic substituents, namely: 2-exo-(5-nitrofuran-2-yl)-2,3,4,5-tetrahydro-1,4-epoxy-1H-1-benzazepine, C(14)H(12)N(2)O(4), (I), 7-fluoro-2-exo-(1-methyl-1H-pyrrol-2-yl)-2,3,4,5-tetrahydro-1,4-epoxy-1H-1-benzazepine, C(15)H(15)FN(2)O, (II), 7-fluoro-2-exo-(5-methylfuran-2-yl)-2,3,4,5-tetrahydro-1,4-epoxy-1H-1-benzazepine, C(15)H(14)FNO(2), (III), 7-fluoro-2-exo-(3-methylthiophen-2-yl)-2,3,4,5-tetrahydro-1,4-epoxy-1H-1-benzazepine, C(15)H(14)FNOS, (IV), 7-fluoro-2-exo-(5-methylthiophen-2-yl)-2,3,4,5-tetrahydro-1,4-epoxy-1H-1-benzazepine, C(15)H(14)FNOS, (V), 7-chloro-2-exo-(5-methylfuran-2-yl)-2,3,4,5-tetrahydro-1,4-epoxy-1H-1-benzazepine, C(15)H(14)ClNO(2), (VI), 2-exo-(5-methylfuran-2-yl)-7-trifluoromethoxy-2,3,4,5-tetrahydro-1,4-epoxy-1H-1-benzazepine, C(16)H(14)F(3)NO(3), (VII), 2-exo-(3-methylthiophen-2-yl)-7-trifluoromethoxy-2,3,4,5-tetrahydro-1,4-epoxy-1H-1-benzazepine, C(16)H(14)F(3)NO(2)S, (VIII), and 2-exo-(5-nitrofuran-2-yl)-7-trifluoromethoxy-2,3,4,5-tetrahydro-1,4-epoxy-1H-1-benzazepine, C(15)H(11)F(3)N(2)O(5), (IX). All nine compounds crystallize in centrosymmetric space groups as racemic mixtures with configuration (2RS,4SR). There are no direction-specific interactions between the molecules in (V). The molecules in (III), (IV), (VI) and (VII) are linked into simple chains, by means of a single C-H...O hydrogen bond in each of (III), (VI) and (VII), and by means of a single C-H...π(arene) hydrogen bond in (IV), while the molecules in (VIII) are linked into a chain of rings. In each of (I) and (II), a combination of one C-H...O hydrogen bond and one C-H...π(arene) hydrogen bond links the molecules into sheets, albeit of completely different construction in the two compounds. In (IX), the sheet structure is built from a combination of four independent C-H...O hydrogen bonds and one C-H...π(arene) hydrogen bond. Comparisons are made with some related compounds.