Inclusion complexes of the steroid hormones 17β-estradiol and progesterone with β- and γ-cyclodextrin hosts: syntheses, X-ray structures, thermal analyses and API solubility enhancements

• Alexios I. Vicatos,
• Zakiena Hoossen and
• Mino R. Caira

Beilstein J. Org. Chem. 2022, 18, 1749–1762, doi:10.3762/bjoc.18.184

• γ-CD molecules (A, B, C) comprise the major structural motif in the γ-CD·PRO crystal, and they stack to form infinite columns, arranging themselves in a head-to-tail motif between molecules C and A, a tail-to-tail motif between molecules B and C, and a head-to-head motif between molecules A and B

Preparation of β-cyclodextrin-based dimers with selectively methylated rims and their use for solubilization of tetracene

• Konstantin Lebedinskiy,
• Volodymyr Lobaz and
• Jindřich Jindřich

Beilstein J. Org. Chem. 2022, 18, 1596–1606, doi:10.3762/bjoc.18.170

• moieties (head-to-head interaction, Figure 6b). We suppose this type of interaction results in better complexation with the guest. The synthesized dimers have given us the best results in the experiment. However, it is quite difficult to highlight a trend in this small group because the dimers with

• bonds. The spectrum of 12 clearly belongs to a compound with high symmetry, favoring this interaction and reducing the solubilization efficiency; also, the spacer length might be too short for the "head-to-head" orientation (Figure 6c). Determination of the binding parameters Despite achieving some

• referred to its concentrated solution without any hosts (0). "Tail-to-tail" (a) and "head-to-head" (b) orientation of two cyclodextrin moieties and primary-rim connected CDs with non-interacting rims (c). Isotherms of the titration of tetracene with "dimeric" CD solutions in DMSO at 298 K (circles – 10

Synthesis of novel alkynyl imidazopyridinyl selenides: copper-catalyzed tandem selenation of selenium with 2-arylimidazo[1,2-a]pyridines and terminal alkynes

• Mio Matsumura,
• Kaho Tsukada,
• Kiwa Sugimoto,
• Yuki Murata and
• Shuji Yasuike

Beilstein J. Org. Chem. 2022, 18, 863–871, doi:10.3762/bjoc.18.87

• torsion angle of 10.28°. 2-Phenylimidazo[1,2-a]pyridine moieties of neighboring molecules were arranged into slipped-parallel π-stacks with head-to-tail or head-to-head orientations. The distances between parallel mean planes were 3.427 and 3.428 Å (Figure 2b). To demonstrate the efficiency and to broaden

Structural effects of meso-halogenation on porphyrins

• Keith J. Flanagan,
• Maximilian Paradiz Dominguez,
• Zoi Melissari,
• Hans-Georg Eckhardt,
• René M. Williams,
• Dáire Gibbons,
• Caroline Prior,
• Gemma M. Locke,
• Alina Meindl,
• Aoife A. Ryan and
• Mathias O. Senge

Beilstein J. Org. Chem. 2021, 17, 1149–1170, doi:10.3762/bjoc.17.88

• both show a preference for interacting in a head-to-head fashion with a Br···H interaction seen between the bromine atoms and the pyrrole unit for 6 (Figure 12A) or the hexyl chain for 7 (Figure 12B) (see Table 1 for distances and angles). However, the main feature of this type is the packing, where

• Supporting Information File 1, Figure S33. The first two (Supporting Information File 1, Figure S32A and B) are directed through alkyl interactions with a head-to-head overlap (Supporting Information File 1, Figure S32A) and the stacked system (Supporting Information File 1, Figure S32B). The third motif is

• the close-packed side-on alignment which is due to the space occupied by the bromine atom, although there is no indication of potential halogen interactions. The final motif is a head-to-head Br···H contact between the porphyrin macrocycles (Supporting Information File 1, Figure S34) which tether the

Insight into functionalized-macrocycles-guided supramolecular photocatalysis

• Minzan Zuo,
• Krishnasamy Velmurugan,
• Kaiya Wang,
• Xueqi Tian and
• Xiao-Yu Hu

Beilstein J. Org. Chem. 2021, 17, 139–155, doi:10.3762/bjoc.17.15

• stacked in a slipped anti- or syn-head-to-tail (HT) fashion) to afford the successive photocyclodimerization, which mimics a catalytic antibody. Therefore, various head-to-head (HH)- or HT-photodimers could be obtained. Particularly, the 21–AC complex could be involved in the photolysis and produced the

4-Hydroxy-3-methyl-2(1H)-quinolone, originally discovered from a Brassicaceae plant, produced by a soil bacterium of the genus Burkholderia sp.: determination of a preferred tautomer and antioxidant activity

• Dandan Li,
• Naoya Oku,
• Yukiko Shinozaki,
• Yoichi Kurokawa and
• Yasuhiro Igarashi

Beilstein J. Org. Chem. 2020, 16, 1489–1494, doi:10.3762/bjoc.16.124

• without a 3-methyl group, and the former lineages are unique to Burkholderia producers [28]. These metabolites are shown to be biosynthesized by head-to-head condensation of anthranilate and β-ketoacylate precursors, followed by a modification at C3 or nitrogen by putative monooxygenases or

Towards triptycene functionalization and triptycene-linked porphyrin arrays

• Gemma M. Locke,
• Keith J. Flanagan and
• Mathias O. Senge

Beilstein J. Org. Chem. 2020, 16, 763–777, doi:10.3762/bjoc.16.70

• [C11 to C16, centroid···centroid distance of 3.755(3) Å and shift distance of 1.593(5) Å] involved in a head-to-head slip plane π-stacking interaction with another triptycene molecule either side, while the third face ring iii of the triptycene exhibits C23–H23B···π interactions between the isopropyl

Self-assembled coordination thioether silver(I) macrocyclic complexes for homogeneous catalysis

• Zhen Cao,
• Aline Lacoudre,
• Cybille Rossy and
• Brigitte Bibal

Beilstein J. Org. Chem. 2019, 15, 2465–2472, doi:10.3762/bjoc.15.239

• highlighted the two possible arrangements of the ligands that led to different diastereoisomeric macrocycles (Figure 1a,b). In Figure 1a, each silver cation was coordinated to two sulfur atoms with the same configuration (named head-to-head coordination mode for ligands) meanwhile in Figure 1b, each Ag(I

• ) cation was coordinated to two sulfur atoms with (R)- and (S)-configuration, respectively (head-to-tail ligand coordination mode). These diastereoisomeric crystals presented a slightly different spatial arrangement. The head-to head macrocycle 1a had a parallelepiped shape (Figure 1a): the interplanar

• the coordinated ligands (head-to-head or head-to-tail) resulting into different spatial arrangements. In solution, the architectures of silver(I) complexes with ligand syn-1 seemed to be similar to the solid-state structures. The silver(I) complexes were evaluated as homogeneous catalysts in two

Crystal structure of the inclusion complex of cholesterol in β-cyclodextrin and molecular dynamics studies

• Elias Christoforides,
• Andreas Papaioannou and
• Kostas Bethanis

Beilstein J. Org. Chem. 2018, 14, 838–848, doi:10.3762/bjoc.14.69

• of cholesterol in β-CD. The inclusion complex crystallizes in the triclinic space group P1 forming head-to-head dimers which are stacked along the c-axis. One well-defined cholesterol molecule ‘axially’ encapsulated inside the β-CD dimer and 22 water molecules that stabilize the complexes in the

• host A and host B) arranged co-axially so that the secondary rim (head) of the one faces the secondary rim of the other forming a head-to-head dimer via intermolecular hydrogen bonds between their O3n-H hydroxy groups. A cholesterol molecule is found fully encapsulated inside the β-CD dimeric cavity

• neighboring units in the extended two-dimensional crystalline array. In the 8-hydroxyquinoline inclusion complex crystal structure (UJEFEV), the asymmetric unit consists of two β-CDs, one 8-hydroxyquinoline, two ethanol and thirty water molecules. The hydrophobic cavities of the two β-CDs forming a head-to

Binding abilities of a chiral calix[4]resorcinarene: a polarimetric investigation on a complex case of study

• Marco Russo and
• Paolo Lo Meo

Beilstein J. Org. Chem. 2017, 13, 2698–2709, doi:10.3762/bjoc.13.268

• the aggregates is not affected by the charge status of the host in a simple way, although data clearly suggest that the tendency to form 2:1 complexes decreases on increasing the charge of the host. The latter observation can be easily justified assuming the occurrence of a head-to-head arrangement

Mechanochemical synthesis of thioureas, ureas and guanidines

• Vjekoslav Štrukil

Beilstein J. Org. Chem. 2017, 13, 1828–1849, doi:10.3762/bjoc.13.178

• : corrugated chains of head-to-head or head-to-tail aligned molecules and discrete centrosymmetric dimers based on the R22(8) supramolecular synthon in the case of sterically hindered thioureas (Figure 2). The crystal structures of N,N'-diarylthioureas linked in chains via N–H···S hydrogen bonds can further be

Pd(OAc)₂/Ph₃P-catalyzed dimerization of isoprene and synthesis of monoterpenic heterocycles

• Dominik Kellner,
• Maximilian Weger,
• Andrea Gini and
• Olga García Mancheño

Beilstein J. Org. Chem. 2017, 13, 1807–1815, doi:10.3762/bjoc.13.175

• formed: tail-to-tail, head-to-tail, tail-to-head and head-to-head (Figure 1). In addition to the linear dimeric products, cyclic monoterpenes such as limonene can also be formed as byproducts. A number of transition metal complexes can be used as catalysts in the dimerization of isoprene. In one hand

• the tail-to-tail linkage [15][29]. Moreover, the naturally occurring head-to-tail 2-HT dimers, myrcene and ocimene, can be obtained in allylic alcohol when employing Pd(NO3)2/Ph3P/KOPh as catalytic system [30]. The head-to-head 2-HH dimer could also be prepared as major isomer under catalysis with the

Molecular recognition of N-acetyltryptophan enantiomers by β-cyclodextrin

• Spyros D. Chatziefthimiou,
• Mario Inclán,
• Petros Giastas,
• Athanasios Papakyriakou,
• Konstantina Yannakopoulou and
• Irene M. Mavridis

Beilstein J. Org. Chem. 2017, 13, 1572–1582, doi:10.3762/bjoc.13.157

• stronger H-bonding of the carboxyl group, as well as more favorable methyl–phenyl interactions inside the cavity. In contrast, no discrimination is shown by β-CD for (R)- and (S)-flurbiprofen [11], since the crystals grown from the racemic mixture have both enantiomers enclosed (as a head-to-head dimer) in

• guest molecules of L-NAcTrp are enclosed in a head-to-head fashion (host:guest ratio, 1:1). The pair of L-NAcTrp molecules inside the dimer are found in orientational disorder, i.e., the guest exhibits a major orientation, molecules C and D (occupancy 65%), and a co-existing minor orientation (molecules

Inclusion complexes of β-cyclodextrin with tricyclic drugs: an X-ray diffraction, NMR and molecular dynamics study

• Franca Castiglione,
• Fabio Ganazzoli,
• Luciana Malpezzi,
• Andrea Mele,
• Walter Panzeri and
• Giuseppina Raffaini

Beilstein J. Org. Chem. 2017, 13, 714–719, doi:10.3762/bjoc.13.70

• )° for 1 and 2, respectively, where the figures in parentheses give the standard errors. The β-CD macrocyclic rings appear slightly distorted upon inclusion of the guest molecule. In the crystal, the arrangement of the complexes formed by 1 and 2 with β-CD are similar, being stacked head-to-head to form

Dimerization reactions of aryl selenophen-2-yl-substituted thiocarbonyl S-methanides as diradical processes: a computational study

• Michael L. McKee,
• Grzegorz Mlostoń,
• Katarzyna Urbaniak and
• Heinz Heimgartner

Beilstein J. Org. Chem. 2017, 13, 410–416, doi:10.3762/bjoc.13.44

• computational methods. The preferred formation of the unusual macroheterocycle, competitive with the 1,3-ring closure leading to a thiirane and the head-to-head dimerization yielding a 1,4-dithiane derivative, respectively, was explained based on the analysis of the structure of the favored conformer of the

• , with no exception, via a head-to-head dimerization yielding sterically crowded 1,4-dithianes of type 5 [9][10]. The analogous head-to-head dimerization course was reported for the thiocarbonyl S-methanide derived from benzyl octafluorodithiopentanoate [11]. The reaction mechanisms of the dimerization

• diaryl thiocarbonyl S-methanides 1. The in situ generation of phenyl selenophen-2-yl S-methanide (8) and its competitive reactions: 1,3-ring closure, head-to-head dimerization, and macroheterocycle 9 formation via an intermediate diradical species 8B–D. Supporting Information Supporting Information File

Chemical probes for competitive profiling of the quorum sensing signal synthase PqsD of Pseudomonas aeruginosa

• Michaela Prothiwa,
• Dávid Szamosvári,
• Sandra Glasmacher and
• Thomas Böttcher

Beilstein J. Org. Chem. 2016, 12, 2784–2792, doi:10.3762/bjoc.12.277

• ]. The biosynthesis of AQs has been matter of a long-standing debate that could only recently be resolved. Although HHQ could be produced in vitro by a PqsD catalyzed “head-to-head” decarboxylative Claisen condensation of activated anthranilic acid with β-keto fatty acid derivatives [10][11], isotope

Radical polymerization by a supramolecular catalyst: cyclodextrin with a RAFT reagent

• Kohei Koyanagi,
• Yoshinori Takashima,
• Takashi Nakamura,
• Hiroyasu Yamaguchi and
• Akira Harada

Beilstein J. Org. Chem. 2016, 12, 2495–2502, doi:10.3762/bjoc.12.244

• close together during the course of RAFT polymerization. Figure S5a (Supporting Information File 1) shows the crystal structure of β-CD with DMA. β-CD formed a head-to-head dimeric structure in the crystal. Figure S5b shows a schematic diagram of the crystal structure of β-CD/DMA. The stoichiometry of β

Comparing blends and blocks: Synthesis of partially fluorinated diblock polythiophene copolymers to investigate the thermal stability of optical and morphological properties

• Pierre Boufflet,
• Sebastian Wood,
• Jessica Wade,
• Zhuping Fei,
• Ji-Seon Kim and
• Martin Heeney

Beilstein J. Org. Chem. 2016, 12, 2150–2163, doi:10.3762/bjoc.12.205

• around 2.65 ppm are likely related to regiochemical defects such as head-to-head or tail-to-tail couplings in the backbone [43], as well as the methylene region from the chain end [44]. Integration of this region with respect to the overall methylene region gives approximate regioregularites of 92 and 97

Diradical reaction mechanisms in [3 + 2]-cycloadditions of hetaryl thioketones with alkyl- or trimethylsilyl-substituted diazomethanes

• Grzegorz Mlostoń,
• Paulina Pipiak and
• Heinz Heimgartner

Beilstein J. Org. Chem. 2016, 12, 716–724, doi:10.3762/bjoc.12.71

• . Remarkably, in no single case, the ‘head-to-head dimerization’ of aryl/hetaryl and dihetaryl substituted thiocarbonyl ylides was observed. Keywords: [3 + 2]-cycloadditions; diazoalkanes; diradicals; 1,3-dithiolanes; reaction mechanisms; thioketones; Introduction Cycloaddition reactions belong to the most

• ). When the decomposition of 2a or 2b was performed in the presence of a suitable dipolarophile, the corresponding [3 + 2]-cycloadducts were formed, whereas in the absence of a dipolarophile, the ‘head-to-head dimerization’ leading to 2,2,3,3-tetraaryl-1,4-dithianes 4a,b is the exclusive reaction

• ; anal. cald for C22H22S6Si (506.89): C, 52.13; H, 4.37; S, 37.96; found: C, 52.44; H, 4.55; S,37.71. ‘Head-to-head dimerization’ of diarylthioketone S-methanides 3a,b leading to 2,2,3,3-tetrasubstituted 1,4-dithianes 4a,b. Diradical nature of the reactive intermediate 3c in the reaction of phenyl

Biosynthesis of α-pyrones

• Till F. Schäberle

Beilstein J. Org. Chem. 2016, 12, 571–588, doi:10.3762/bjoc.12.56

• molecules, e.g., photopyrones (8–15) from Photorhabdus luminescens are synthesized by such a head-to-head condensation of two acyl moieties [60]. Also the csypyrones (79–81, Figure 21), first reported from Aspergillus oryzae, are composed of two independent chains which are interconnected thereafter [85

Versatile deprotonated NHC: C,N-bridged dinuclear iridium and rhodium complexes

• Albert Poater

Beilstein J. Org. Chem. 2016, 12, 117–124, doi:10.3762/bjoc.12.13

• isomers of complex [M(cod){µ-C3H2N2(Mes)-κC2,κN3}]2). The latter two isomers display conformations head-to-head (H-H) and head-to-tail (H-T) of CS and C2 symmetry, respectively. The isomerization from the H-H to the H-T conformation is feasible, whereas next substitutions of the cod ligand by CO first

• , and PMe3 later confirm the H-T coordination as the thermodynamically preferred. It is envisaged the exchange of the metal, from iridium to rhodium, confirming here the innocence of the nature of the metal for such arrangements of the bridging ligands. Keywords: DFT; head-to-head; head-to-tail

• 3H-H and 3H-T (where H-H = head-to-head and H-T = head-to-tail). By DFT calculations here we contribute in the understanding of the thermodynamics of the subsequent C,N-bridged dinuclear iridium and rhodium complexes [59], and the facility for the interconversion between these latter dimeric species

Self-assemblies of γ-CDs with pentablock copolymers PMA-PPO-PEO-PPO-PMA and endcapping via atom transfer radical polymerization of 2-methacryloyloxyethyl phosphorylcholine

• Jing Lin,
• Tao Kong,
• Lin Ye,
• Ai-ying Zhang and
• Zeng-guo Feng

Beilstein J. Org. Chem. 2015, 11, 2267–2277, doi:10.3762/bjoc.11.247

• , C4 and C6 resonance peaks. In the test sample, PEP100M15CD, the corresponding carbon reveals a single resonance peak together with the typical resonance peaks from PMA. This clearly suggested that the γ-CDs were threaded in a head-to-head and tail-to-tail fashion onto the PMA-PPO-PEO-PPO-PMA chain

A novel and widespread class of ketosynthase is responsible for the head-to-head condensation of two acyl moieties in bacterial pyrone biosynthesis

• Darko Kresovic,
• Florence Schempp,
• Zakaria Cheikh-Ali and
• Helge B. Bode

Beilstein J. Org. Chem. 2015, 11, 1412–1417, doi:10.3762/bjoc.11.152

• , 60438 Frankfurt am Main, Germany 10.3762/bjoc.11.152 Abstract The biosynthesis of photopyrones, novel quorum sensing signals in Photorhabdus, has been studied by heterologous expression of the photopyrone synthase PpyS catalyzing the head-to-head condensation of two acyl moieties. The biochemical

• photopyrone synthase (PpyS), which catalyzes the head-to-head condensation of two acyl moieties. Ketosynthases (KS) are the key enzymes involved in the biosynthesis of fatty acids and polyketides [8]. They are known to catalyze C–C bond formations via a Claisen condensation between acyl- and malonylthioesters

• OleA, which is part of the olefin biosynthesis in Xanthomonas campestris by promoting a head-to-head condensation of two long-chain fatty acid thioesters to form a long-chain β-ketoacid that can be further processed to an olefin [14]. KS with acylating activity have been reported in the cervimycin [15

Synthesis and characterization of the cyanobenzene-ethylenedithio-TTF donor

• Sandrina Oliveira,
• Dulce Belo,
• Isabel C. Santos,
• Sandra Rabaça and
• Manuel Almeida

Beilstein J. Org. Chem. 2015, 11, 951–956, doi:10.3762/bjoc.11.106

• crystal structure is made by piling up molecules head to head forming stacks along the b axis (Figure 2) with short S–H contacts (S1–H1B; S4–H2B) in the range 2.751–2.824 Å. Neighbouring stacks are arranged head to tail in the a,c plane with several short contacts between molecules in neighbouring stacks

TTFs nonsymmetrically fused with alkylthiophenic moieties

• Rafaela A. L. Silva,
• Bruno J. C. Vieira,
• Marta M. Andrade,
• Isabel C. Santos,
• Sandra Rabaça,
• Dulce Belo and
• Manuel Almeida

Beilstein J. Org. Chem. 2015, 11, 628–637, doi:10.3762/bjoc.11.71

• methyl group which prevent a shorter distance between molecular planes. Within the stacks the donor molecules are head-to-head (Figure 8). The interactions between stacks are made in two distinct ways along the molecules long axis: 1) In one side the donor molecules interact, with each other, through the