Chiral solid state

Achiral objects can be assembled into chiral solid-state structures, and this is frequently the case for urea 1 when it encloses guests. Other compounds adopt a chiral conformation in solution and therefore may ultimately produce either chiral or achiral host structures. On the other hand, thiourea 2 forms an inclusion lattice that is achiral. This arrangement is nonetheless very effective in enclosing guest molecules. 

Chiral Solid-State Photochemistry Including Supramolecular Approaches... 

Koshima, H., Chiral Solid state Photochemistry Including Supramolecular Approaches. In Inoue, Y., Ramamurthy, V. (eds), Chiral Photochemistry, Vol. 11, Marcel Dekker, New York, 2004, pp. 485 532. 

The self-assembly of an optically active [2]catenane involved the incoiporation of a chiral hydrobenzoin unit into one of its component rings one of the p-xylyl groups in the tetracationic cyclophane may be substituted by a flexible CH2CX H2CH20CH2CH2 chain without impeding catenane formation (Scheme 18). However, when both the p-xylyl units are replaced, the tetracationic cyclophane loses its ability to complex with Tc-electron rich aromatic substrates. This achievement has implications for the design of chiral solid-state devices and the construction of asymmetric catalysts. 

Irradiation of 3,6-bridged oxepins with ester functions in the 4- and 5-positions gives tricyclic structures 3 in which the oxepin oxygen becomes part of an aldehyde function.248-250 When chiral esters are used, it has been shown that the irradiation in solid state proceeds with a high degree of diastereoselectivity.249,251,252... 

Polylactides, 18 Poly lactones, 18, 43 Poly(L-lactic acid) (PLLA), 22, 41, 42 preparation of, 99-100 Polymer age, 1 Polymer architecture, 6-9 Polymer chains, nonmesogenic units in, 52 Polymer Chemistry (Stevens), 5 Polymeric chiral catalysts, 473-474 Polymeric materials, history of, 1-2 Polymeric MDI (PMDI), 201, 210, 238 Polymerizations. See also Copolymerization Depolymerization Polyesterification Polymers Prepolymerization Repolymerization Ring-opening polymerization Solid-state polymerization Solution polymerization Solvent-free polymerization Step-grown polymerization processes Vapor-phase deposition polymerization acid chloride, 155-157 ADMET, 4, 10, 431-461 anionic, 149, 174, 177-178 batch, 167 bulk, 166, 331 chain-growth, 4 continuous, 167, 548 coupling, 467 Friedel-Crafts, 332-334 Hoechst, 548 hydrolytic, 150-153 influence of water content on, 151-152, 154... 

This is only the beginning of a process which ultimately results in the formation of solid state hydroxides or oxides. Actually, the solution species present in neutral or alkaline solutions of transition-metal ions are relatively poorly characterized. The formation of numerous hydroxy- and oxy-bridged polynuclear species makes their investigation very difficult. However, it is clear that there is a near-continuous transition from mononuclear solution species, through polynuclear solution species to colloidal and solid state materials. By the way, the first example of a purely inorganic compound to exhibit chirality was the olated species 9.11. 

These studies conducted in solution and in the solid state revealed a common 3i4-helical fold stabilized by H-bonds closing 14-membered rings formed between NH and C=0 +2 (see Fig. 2.12A and C). It is noteworthy that the 3i4-helix of j -peptides with L-amino acid-derived chirality centers (Fig. 2.12 A) and the a-helix have opposite polarity and helicity. 

A regio- and stereoselective Beckmann rearrangement utilized diastereose-lective host guest interactions of the inclusion complexes 225 and 228 in a solid state reaction. Initially, a 1 1 mixture of the chiral host 223 and the racemic oximes 224 and 227, respectively, was treated with ultra sound in the solid state to induce the optical resolution. Then H2SO4 was added to start the Beckmann rearrangement, the corresponding c-caprolactams 226 and 229 were isolated in 68 % and 64 % yields and ee of about 80 % and 69 % (determined by HPLC analysis on chiracel OC) (Scheme 43) [46]. 

An enantioselective Michael addition reaction was also accomplished in an inclusion complex with a chiral host compound. Treatment of a 1 1 complex of 10c and 66b with 2-mercaptopyridine (137) in the solid state gave (+)-138 of 80% ee in 51% yield. By a similar method, 3-methyl-3-buten-2-one (139) gave (+)-140 of 49% ee in 76% yield [30]. 

Photoirradiation of both neat and benzene solutions of 2-cyclohexenone (66b) gives a complex mixture of photodimers [40]. However, photoirradiation of a 1 1 complex of 66b with the chiral host (S,S)-(-)-l,4-bis[3-(o-chlorophenyl)-3-hydroxy-3-phenylprop-l-ynyl]benzene (167) in the solid state (Scheme 24) gave (-)-anf/-head-to-head dimer 168 of 46% ee in 75% yield [40]. This reaction was found to proceed in a single crystal-to-single crystal manner. The mechanism of the reaction was studied by X-ray crystal structural analysis [41]. 

As indicated above in chiral mesophases, the introduction of a functional group in mesogenic stmctures offers the opportunity to achieve functional LCs. With this aim, mesomorphic crown-ether-isocyanide-gold(I) complexes (26) have been prepared recently [38]. The derivatives with one alkoxy chain show monotropic SmC mesophases at or close to room temperature. In contrast, the complexes with three alkoxy chains behave as monotropic (n = 4) or enantiotropic (n > 4) LCs. The structure of the mesophases could not be fully eluddated because X-ray diffraction studies in the mesophase were unsuccessful and mesophase characterization was made only on the basis of polarized optical microscopy. These complexes are luminescent not only in the solid state and in solution, but also in the mesophase and in the isotropic liquid state at moderate temperatures. The emission spectra of 26a with n=12 were... 

Scheffer JR, Xia W (2005) Asymmetric Induction in Organic Photochemistry via the Solid-State Ionic Chiral Auxiliary Approach. 254 233-262 Schenning APHJ, see Ajayaghosh A (2005) 258 83-118 Schepers U, see Hahn F (2007) 278 135-208 Schindler J, see Faigl F (2007) 269 133-157... 

In the solid state, (149a) with R1 = R2 = Pr1 and R3 = H is a dimer with two /r-bromo linkages and five-coordinate Ni11 ions.540 Precatalysts (152) with very bulky 2,6-diphenylaniline substituents (R = But, OMe) adopt a chiral C2 symmetry due to repulsive interactions between the sterically demanding groups.541... 

The zinc complex of 1,1,1,5,5,5-hexafluoroacetylacetonate forms coordination polymers in reaction with either 2,5-bis(4-ethynylpyridyl)furan or l,2-bis(4-ethynylpyridyl)benzene. The X-ray crystal structures demonstrate an isotactic helical structure for the former and a syndio-tactic structure for the latter in the solid state. Low-temperature 1H and 19F NMR studies gave information on the solution structures of oligomers. Chiral polymers were prepared from L2Zn where L = 3-((trifluoromethyl)hydroxymethylene)-(+)-camphorate. Reaction with 2,5-bis(4-ethy-nylpyridyl)furan gave a linear zigzag structure and reaction with tris(4-pyridyl)methanol a homo-chiral helical polymer.479... 

The chiral l,3,5-triazepane-2,6-dione 149 and its ring fused analogue 150 have been shown to form H-bonded helical molecular tapes with P chirality on self assembly in the solid state. With 149, this self assembly proceeds through aromatic-aromatic ring interactions resulting in hollow tubular structures <06CC4069>. 

Nuclear magnetic resonance (NMR) spectroscopy in pharmaceutical research has been used primarily in a classical, organic chemistry framework. Typical studies have included (1) the structure elucidation of compounds [1,2], (2) investigating chirality of drug substances [3,4], (3) the determination of cellular metabolism [5,6], and (4) protein studies [7-9], to name but a few. From the development perspective, NMR is traditionally used again for structure elucidation, but also for analytical applications [10]. In each case, solution-phase NMR has been utilized. It seems ironic that although —90% of the pharmaceutical products on the market exist in the solid form, solid state NMR is in its infancy as applied to pharmaceutical problem solving and methods development. 

The solubility behavior of enantiomers and racemates has been reviewed by Jacques et al. [141]. Other solid state properties of chiral drugs have been reviewed by Brittain [142]. 

---