X-ray crystal structure analyses

Wang, D., Bode, W., Huber, R. Bovine chymotrypsinogen A. X-ray crystal structure analysis and refinement of a new crystal form at 1.8 A resolution. /. Mol. Biol. 

The alkaloid Nigellicine proved to be the pyridazino[l,2-u]indazolium-l 1-carboxylate (234) and forms yellow crystals (Scheme 77). It was isolated from the widely distributed herbaceous plant Nigella saliva L., which is used as a spice and for the treatment of various diseases (85TL2759). The structure was determined by an X-ray crystal structure analysis. The carboxylate bond distances are essentially equal (123.3 and 125.6 pm). An intramolecular hydrogen bond was found between the carboxylate oxygen atom and the hydroxy group. In mass spectrometry, the molecular peak was found at mjz —246 (20) and the base peak at mjz —202 which corresponds... 

Precipitated K—salt crystals are carefully filtrated and washed so as to separate them from the mother solution. Drying of filtrated K-salt is also a very delicate and important process that must be performed under conditions that avoid hydrolysis of the material. Potassium heptafluorotantalate is sensitive to water, basic compounds and alcohols, especially at elevated temperatures. The main product of K-salt hydrolysis is Marignac s salt. For a long time it was believed that the composition of Marignac s salt is K/Ta Fg. However, X-ray crystal structure analysis and precise chemical analysis of the... 

The absolute (25,1 i ) configuration of these products was established by chemical correlation and X-ray crystal structure analysis of a prehydrolysis adduct30. 

The novel highly substituted spiro[4.4]nonatrienes 98 and 99 are produced by a [3+2+2+2] cocyclization with participation of three alkyne molecules and the (2 -dimethylamino-2 -trimethylsilyl)ethenylcarbene complex 96 (Scheme 20). This transformation is the first one ever observed involving threefold insertion of an alkyne and was first reported in 1999 by de Meijere et al. [81]. The structure of the product was eventually determined by X-ray crystal structure analysis of the quaternary ammonium iodide prepared from the regioisomer 98 (Ar=Ph) with methyl iodide. Interestingly, these formal [3+2+2+2] cycloaddition products are formed only from terminal arylacetylenes. In a control experiment with the complex 96 13C-labeled at the carbene carbon, the 13C label was found only at the spiro carbon atom of the products 98 and 99 [42]. 

Reaction of Ph2PLi with Pr N = C = NPr in THF proceeds via insertion of the carbodiimide into the Li-P bond, affording the lithium phosphaguanidinate salt Li[Ph2PC(NPr )2] in 72% yield. The preparation and reactivity of this new ligand are summarized in Scheme 217. An X-ray crystal structure analysis of the product obtained after removal of the solvent from the reaction mixture revealed the presence of a mono-solvated, centrosymmetric dimer in the solid state (Figure... 

As was suggested in the preceding discussion, most of the arene complexes isolated by metal-atom techniques are benzene derivatives. However, heterocyclic ligands are also known to act as 5- or 6-electron donors in transition-metal 7r-complexes (79), and it has proved possible to isolate heterocyclic complexes via the metal-atom route. Bis(2,6-di-methylpyridine)Cr(O) was prepared by cocondensation of Cr atoms with the ligand at 77 K (79). The red-brown product was isolated in only 2% yield the stoichiometry was confirmed by mass spectrometry, and the structure determined by X-ray crystal-structure analysis, which supported a sandwich formulation. 

The research work described here was carried out by an able group of students of Yamaguchi University and Ube Techinical College, and in collaboration with our laboratory staffs and industrial colleagues. In particular, Dr. S. Fujisaki and Dr. T. Okamoto made significant contributions. We thank them all, and also Dr. H. Tsuzuki of Central Analytical Center of Kyushu University undertook X-ray crystal structure analysis of BTMA Br3. Furthermore, we wish to thank Professor M. Tashiro of Kyushu University for useful discussions. Finally, we are grateful to Professor Y. Sasson of The Hebrew University of Jerusalem, Chairman of the Scientific Committee of Orgabrom 93, for the invitation to present this work in Jerusalem. 

The absolute configuration of (—)-29 was established by X-ray crystal structure analysis of the bromolactone (89), which was prepared from (—)-29 by bromolactonization with hypobromous acid. It was found that ( )-29 belongs to the d series of carba-sugars, and hence, (+)-29 corresponds to the L series. - ... 

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]. 

The (EDT-TTF-I)2Br salt described above [36] and the 1 1 (TTFI4)I salt reported by Gompper [51] were the only structurally characterized salts with simple halide anions until Imakubo recently described an extensive series of Cl" and Br" salts from several ortho-diiodo tetrathiafulvalene, tetraselena-fulvalene and dithiadiselenafulvalene derivatives (Scheme 8) [62], The X-ray crystal structure analysis of the nine salts described there show a variety of halogen bonded motifs, demonstrating the adaptability of the supramolecu-lar interactions to other structural requirements imposed by the nature of the heteroatoms (O, S, Se) in the TTF frame. Indeed, in (EDT-TTF-l2)2X-(H20)2 (X = Cl, Br), a bimolecular motif (Fig. 6) associates two partially oxidized EDT-TTF-I2 molecules with one Br" anion and one water molecule. 

Trimethylenemethane is a special type of alkene that does not exist as the free compound. Various synthetic equivalents to the synthon 43 shown below have been reported. Trost, in particular, has exploited these compounds in 1,3-dipolar cycloaddition reactions.138 139 A metal-bound, isolated trimethylenemethane species was recently reported by Ando (Scheme 6). It resulted from the complexation of an ero-methylenesila-cyclopropene with group 8 carbonyls (Fe, Ru).140,140a The structure was proved by X-ray crystal structure analysis.29Si NMR data were consistent with the -structure shown. 

X-Ray crystal structural analysis of a (+)-erystal of 96 shows that molecules of 96 are arranged so as to be chiral in the crystalline lattice (Fig. 14). Scheme 9 which is depicted by referring to Fig. 14 indicates the reason why each chiral crystal of 96 gives the corresponding chiral 97. 

Seebach and Brenner have found that titanium enolates of acyl-oxazolidinones are added to aliphatic and aromatic nitroalkenes in high diastereoselectivity and in good yield. The effect of bases on diastereoselectivity is shown in Eq. 4.59. Hydrogenation of the nitro products yields y-lactams, which can be transformed into y-amino acids. The configuration of the products is assigned by comparison with literature data or X-ray crystal-structure analysis. 

Apart from the gold(i) system, bis(mesityl)mercury(ii), which also possesses a heavy metal center with strong relativistic effects, has been used for the synthesis of the mixed metal silver(i) aryl complexes, [HgAg2(mes)X2]2 (X = OTf 13a (Figure 7), C104 13b).33 X-ray crystal structure analysis of 13a revealed its hexanuclear nature with the... 

Hydroxy-7-phenylindeno[l,2-A]-l,2,5-oxadiazolo[3,4- /]pyridine can have four polymorphic forms in the solid state, of which two are yellow and two are red. Two of them are interconvertible (yellow/red) upon exposure to different solvents. X-ray crystal structure analysis of one of the red forms shows the phenyl ring and the indenoox-adiazolopyridine ring to be coplanar <1999H(50)895>. 

The structures of two formal trimers of cyanogen iV-oxide of the composition CfNAT were established by X-ray crystal structure analysis. In the crystals, the two rings are almost but not quite coplanar, with dihedral angles of 4.56(0.59)° in the case of structure 4 and 9.43(0.17)° in the case of structure 5 <2000J(P2)473>. 

The reaction of 1 with the boron trihalides BC13 and BBr3 turned out to be even more complex. At least three different types of compounds were formed, and the product ratio depended on the polarity of the solvent.30 In the reaction with BBr3 in dichloromethane/hexane (2 1), the boron compound 50 (X = Br) was isolated as the main product (Scheme 12) X-ray crystal structure analysis revealed the presence of a novel arachno-type cluster possessing a BC4 framework (Fig. 8). 

Insertion and rearrangement steps were also observed in the reaction of 1 with B2C1443 (Scheme 14). Compounds 52 and 53 were characterized by NMR spectroscopic or mass-spectrometric data, compound 54 by an X-ray crystal structure analysis. 54 may be regarded as a borane-stabilized boranediyl, consisting of a Me5C5B nido-cluster unit (Fig. 8). 

Benzo-flw-triazine tri-N-oxides 384 (R = H, Me R1 = mesityl, 2,6-ClC6H3) are formed from the reaction of nitrile oxides R CNO with benzofuroxans 385. The structure of 384 (R = Me, R1 = mesityl) has been confirmed by X-ray crystal structure analysis (431). 

Ogura and coworkers178,179 continued their study of the addition of lithiated heterocycles to 2,3 5,6-di-0-isopropylidene-L-gulono-l,4-lactone (50) and related compounds. In the case of the addition of lithiated 1,3-dithiane to 50, it was shown178 by X-ray crystal-structure analysis that l-(l,3-dithian-2-yl)-2,3 5,6-di-0-isopropylidene-/3-L-gulofuranose is R at the anomeric carbon atom. This demonstrates that the product of this reaction is, surprisingly, the more sterically hindered of the two products possible. This is the opposite of that predicted for addition of the lithiated dithiane from the less hindered side of 50 if no equilibration of the initial adduct is involved. 

The 11-vertex /0-diphosphaborane [7,9-Ph2- ri/ -7,9-P2B9H9] 35 was synthesized in 20% yield from [B9H12] and PhPCl2 and was characterized by NMR spectroscopy and X-ray crystal structure analysis.141... 

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