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1.
Grald Lelais Peter Micuch Delphine Josien‐Lefebvre Francesco Rossi Dieter Seebach 《Helvetica chimica acta》2004,87(12):3131-3159
The Ser, Cys, and His side chains play decisive roles in the syntheses, structures, and functions of proteins and enzymes. For our structural and biomedical investigations of β‐peptides consisting of amino acids with proteinogenic side chains, we needed to have reliable preparative access to the title compounds. The two β3‐homoamino acid derivatives were obtained by Arndt–Eistert methodology from Boc‐His(Ts)‐OH and Fmoc‐Cys(PMB)‐OH (Schemes 2–4), with the side‐chain functional groups' reactivities requiring special precautions. The β2‐homoamino acids were prepared with the help of the chiral oxazolidinone auxiliary DIOZ by diastereoselective aldol additions of suitable Ti‐enolates to formaldehyde (generated in situ from trioxane) and subsequent functional‐group manipulations. These include OH→OtBu etherification (for β2hSer; Schemes 5 and 6), OH→STrt replacement (for β2hCys; Scheme 7), and CH2OH→CH2N3→CH2NH2 transformations (for β2hHis; Schemes 9–11). Including protection/deprotection/re‐protection reactions, it takes up to ten steps to obtain the enantiomerically pure target compounds from commercial precursors. Unsuccessful approaches, pitfalls, and optimization procedures are also discussed. The final products and the intermediate compounds are fully characterized by retention times (tR), melting points, optical rotations, HPLC on chiral columns, IR, 1H‐ and 13C‐NMR spectroscopy, mass spectrometry, elemental analyses, and (in some cases) by X‐ray crystal‐structure analysis. 相似文献
2.
Rui M. A. Pinto Jorge A. R. Salvador Jos A. Paixo 《Acta Crystallographica. Section C, Structural Chemistry》2008,64(5):o279-o282
In the title compounds, C21H30O4, (I), and C23H34O4, (II), respectively, which are valuable intermediates in the synthesis of important steroid derivatives, rings A and B are cis‐(5β,10β)‐fused. The two molecules have similar conformations of rings A, B and C. The presence of the 5β,6β‐epoxide group induces a significant twist of the steroid nucleus and a strong flattening of the B ring. The different C17 substituents result in different conformations for ring D. Cohesion of the molecular packing is achieved in both compounds only by weak intermolecular interactions. The geometries of the molecules in the crystalline environment are compared with those of the free molecules as given by ab initio Roothan Hartree–Fock calculations. We show in this work that quantum mechanical ab initio methods reproduce well the details of the conformation of these molecules, including a large twist of the steroid nucleus. The calculated twist values are comparable, but are larger than the observed values, indicating a possible small effect of the crystal packing on the twist angles. 相似文献
3.
Giuditta Bartalucci Charles Delroy Stuart Fisher Madeleine Helliwell Synnve Liaaen‐Jensen 《Acta Crystallographica. Section C, Structural Chemistry》2008,64(3):o128-o131
13‐cis‐β,β‐Carotene, C40H56, crystallizes with a complete molecule in the asymmetric unit, whereas 15‐cis‐β,β‐carotene, also C40H56, has twofold symmetry about an axis through the central bond of the polyene chain. The polyene methyl groups are arranged on one side of the polyene chains for each molecule and the 6‐s‐cisβ end groups, with the cyclohexene rings in half‐chair conformations, are twisted out of the planes of the polyene chains by angles ranging from 41.37 (17) to 52.2 (4)°. The molecules in each structure pack so that the arms of one occupy the cleft of the next, and there is significant π–π stacking of the almost‐parallel polyene chains of the 15‐cis isomer, which approach at distances of 3.319 (1)–3.591 (1) Å. 相似文献
4.
Wenhui Zhang Bruce C. Noll Anthony S. Serianni 《Acta Crystallographica. Section C, Structural Chemistry》2007,63(10):o578-o581
The β‐pyranose form, (III), of 3‐deoxy‐d ‐ribo‐hexose (3‐deoxy‐d ‐glucose), C6H12O5, crystallizes from water at 298 K in a slightly distorted 4C1 chair conformation. Structural analyses of (III), β‐d ‐glucopyranose, (IV), and 2‐deoxy‐β‐d ‐arabino‐hexopyranose (2‐deoxy‐β‐d ‐glucopyranose), (V), show significantly different C—O bond torsions involving the anomeric carbon, with the H—C—O—H torsion angle approaching an eclipsed conformation in (III) (−10.9°) compared with 32.8 and 32.5° in (IV) and (V), respectively. Ring carbon deoxygenation significantly affects the endo‐ and exocyclic C—C and C—O bond lengths throughout the pyranose ring, with longer bonds generally observed in the monodeoxygenated species (III) and (V) compared with (IV). These structural changes are attributed to differences in exocyclic C—O bond conformations and/or hydrogen‐bonding patterns superimposed on the direct (intrinsic) effect of monodeoxygenation. The exocyclic hydroxymethyl conformation in (III) (gt) differs from that observed in (IV) and (V) (gg). 相似文献
5.
R. M. A. Pinto M. Ramos Silva A. Matos Beja J. A. R. Salvador J. A. Paixo 《Acta Crystallographica. Section C, Structural Chemistry》2009,65(5):o214-o216
In the title compound, C23H34O4, which is an intermediate in the synthesis of pregnane derivatives with a modified skeleton that show potent abortion‐inducing activity, the conformation of ring B is close to half‐chair due to the presence of both the C=C double bond and the axial 5β‐methyl group. Rings A and C have conformations close to chair, while ring D has a twisted conformation around the bridgehead C—C bond. Molecules are hydrogen bonded via the hydroxyl and acetoxy groups into infinite chains. Quantum‐mechanical ab initio Roothan Hartree–Fock calculations show that crystal packing might be responsible for the low values of the angles between rings A and B, and between ring A and rings C and D, as well as for a different steric position of the methyl ketone side chain compared to the geometry of the free molecule. 相似文献
6.
7.
Lea Glaar Marjeta Radiek Primo egedin Amalija Golobi
《Acta Crystallographica. Section C, Structural Chemistry》2005,61(12):m526-m528
In the title compound, [Cu2(CHO2)2(C5H4NO)2(C5H5NO)2]·1.02CH3CN, the dimeric unit is centrosymmetric, with two bidentate pyridin‐2‐olate and two bidentate formate syn–syn bridges, and two apical 2‐pyridone ligands coordinated through the O atoms. The N atom from the apical 2‐pyridone ligand is a donor of a hydrogen bond to the O atom of the bridging pyridinolate ligand of the same complex. The coordination polyhedron of the Cu atom is a distorted square pyramid. 相似文献
8.
The preparation of three new N‐Fmoc‐protected (Fmoc=[(9H‐fluoren‐9‐yl)methoxy]carbonyl) β2‐homoamino acids with proteinogenic side chains (from Ile, Tyr, and Met) is described, the key step being a diastereoselective amidomethylation of the corresponding Ti‐enolates of 3‐acyl‐4‐isopropyl‐5,5‐diphenyloxazolidin‐2‐ones with CbzNHCH2OMe/TiCl4 (Cbz=(benzyloxy)carbonyl) in yields of 60–70% and with diastereoselectivities of >90%. Removal of the chiral auxiliary with LiOH or NaOH gives the N‐Cbz‐protected β‐amino acids, which were subjected to an N‐Cbz/N‐Fmoc (Fmoc=[(9H‐fluoren‐9‐yl)methoxy]carbonyl) protective‐group exchange. The method is suitable for large‐scale preparation of Fmoc‐β2hXaa‐OH for solid‐phase syntheses of β‐peptides. The Fmoc‐amino acids and all compounds leading to them have been fully characterized by melting points, optical rotations, IR, 1H‐ and 13C‐NMR, and mass spectra, as well as by elemental analyses. 相似文献
9.
R. Hema V. Parthasarathi S. Thamotharan S. Dubey D. P. Jindal 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(7):o421-o422
In the title compound, C31H40N2O·H2O, the outer two six‐membered rings are in chair conformations, while the central ring is in an 8β,9α‐half‐chair conformation. The five‐membered ring adopts a 13β‐envelope conformation and the cyanobenzylidene moiety has an E configuration with respect to the hydroxyl group at position 17. The steroid nuclei are linked by intermolecular O—H?O and O—H?N hydrogen bonds to form a molecular network. The molecular packing has an interesting feature, with the steroids aligned parallel to the b axis, forming a closed loop through hydrogen bonds linked via water molecules. 相似文献
10.
11.
Xiaosong Hu Wenhui Zhang Allen G. Oliver Anthony S. Serianni 《Acta Crystallographica. Section C, Structural Chemistry》2011,67(4):o146-o150
Methyl 2‐acetamido‐2‐deoxy‐β‐d ‐glucopyranoside (β‐GlcNAcOCH3), (I), crystallizes from water as a dihydrate, C9H17NO6·H2O, containing two independent molecules [denoted (IA) and (IB)] in the asymmetric unit, whereas the crystal structure of methyl 2‐formamido‐2‐deoxy‐β‐d ‐glucopyranoside (β‐GlcNFmOCH3), (II), C8H15NO6, also obtained from water, is devoid of solvent water molecules. The two molecules of (I) assume distorted 4C1 chair conformations. Values of ϕ for (IA) and (IB) indicate ring distortions towards BC2,C5 and C3,O5B, respectively. By comparison, (II) shows considerably more ring distortion than molecules (IA) and (IB), despite the less bulky N‐acyl side chain. Distortion towards BC2,C5 was observed for (II), similar to the findings for (IA). The amide bond conformation in each of (IA), (IB) and (II) is trans, and the conformation about the C—N bond is anti (C—H is approximately anti to N—H), although the conformation about the latter bond within this group varies by ∼16°. The conformation of the exocyclic hydroxymethyl group was found to be gt in each of (IA), (IB) and (II). Comparison of the X‐ray structures of (I) and (II) with those of other GlcNAc mono‐ and disaccharides shows that GlcNAc aldohexopyranosyl rings can be distorted over a wide range of geometries in the solid state. 相似文献
12.
L. C. R. Andrade J. A. Paixo M. J. M. De Almeida F. M. Fernandes Roleira E. J. Tavares da Silva 《Acta Crystallographica. Section C, Structural Chemistry》2005,61(3):o131-o133
The title compounds, both C23H34O5, are the 5α and 5β configurations of two diacetate epimers. The 5β‐diacetate crystallizes in an hexagonal structure, unusual for steroid molecules. The unit cell has an accessible solvent volume of 358 Å3, responsible for clathrate behaviour. The 5β‐epimer also features some shorter than average bond lengths in the 3α,4β‐acetoxy groups. The conformations of the molecules of both epimers are compared with those obtained through abinitio quantum chemistry calculations. Cohesion of the crystals can be attributed to van der Waals and weak molecular C—H⋯O interactions. 相似文献
13.
Srinivas Tekkam Joseph L. Johnson Subash C. Jonnalagadda Venkatram R. Mereddy 《Journal of heterocyclic chemistry》2013,50(4):955-958
A concise protocol for the synthesis of α‐methylene‐β‐hydroxy‐γ‐carboxy‐γ‐lactams has been described via alkylation of amino acid derived iminoesters with α‐bromomethylmethacrylate, followed by allylic hydroxylation. All the synthesized compounds have been evaluated for their cytotoxicity on multiple myeloma cancer cell lines. 相似文献
14.
. H. Üngren M. Samaci Y. Akamur C. Arici D. Ülkü 《Journal of heterocyclic chemistry》2005,42(4):685-689
A convenient procedure for the preparation of carbamate derivatives of 5‐oxo‐2,5‐dihydrofuran ( 3 ) was described. The method is based on the Michael type addition of three alkyl carbamates ( 2 ) with 4‐acetyl‐5‐methyl‐2,3‐dihydro‐2,3‐furandione ( 1 ). According to 1H nmr spectra of compounds show tautomeric forms ( 3,4,5 ) in CDC13. In the solid state the synthesized compounds are enol forms ( 3 ). The products were characterized with molecular spectroscopic methods. 相似文献
15.
In‐Chul Hwang Jung Hee Jang Taek Hyeon Kim Kwang Ha 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(4):o196-o198
The molecule of the title compound, C16H21NO4, is chiral and has three asymmetric centres. The absolute configuration was not determined via diffraction measurements on the crystal, but was established from the known absolute configuration of the starting material. In the crystal structure, the molecules assemble through intermolecular hydrogen bonds into a macrostructure with helical channels. 相似文献
16.
J. I. F. Paixo J. A. R. Salvador J. A. Paixo A. Matos Beja M. Ramos Silva A. M. d'A. Rocha Gonsalves 《Acta Crystallographica. Section C, Structural Chemistry》2004,60(9):o630-o632
In the title compound, C21H31N3O4, a potential inhibitor of aromatase, all rings are fused trans. Rings A, B and C have chair conformations which are slightly flattened. Ring D has a 14α‐envelope conformation. The steroid nucleus has a small twist, as shown by the C19—C10⋯C13—C18 torsion angle of 6.6 (2)°. Ab initio calculations of the equilibrium geometry of the molecule reproduce this small twist, which appears to be due to the steric effect of the 6β‐azide substituent rather than to packing effects. 相似文献
17.
The H2O‐soluble cyclic β3‐tripeptide cyclo(β‐Asp‐β3‐hVal‐β3‐hLys) ( 4 ) was obtained by on‐resin cyclization of the side‐chain‐anchored β‐peptide 3 (Scheme). In aqueous solution, 4 adopts a structure with uniformly oriented amide bonds and all side chains in lateral positions (Fig. 3). 相似文献
18.
Zdenko Hamerak Dajana Gao Spomenka Kova
Antonija Hergold‐Brundi Ivan Vickovi Vitomir unji 《Helvetica chimica acta》2003,86(6):2247-2257
Aldol reaction of 7‐chloro‐1,3‐dihydro‐1‐methyl‐5‐phenyl‐2H‐1,4‐benzodiazepin‐2‐one ( 1 ) with 4‐substituted α‐methylcinnamaldehydes 2 – 5 afforded a mixture of threo‐ and erythro‐3‐(3‐aryl‐1‐hydroxy‐2‐methylprop‐2‐enyl)‐7‐chloro‐1,3‐dihydro‐1‐methyl‐5‐phenyl‐2H‐1,4‐benzodiazepin‐2‐ones 6 – 13 . The chromatographically separated threo diastereoisomers 6, 8, 10 , and 12 and erythro diastereoisomers 7, 9, 11 , and 13 were submitted to ‘directed' homogeneous hydrogenation catalyzed by [RhI(cod)(diphos‐4)]ClO4 (cod=cycloocta‐1,5‐diene, diphos‐4=butane‐1,4‐diylbis[diphenylphosphine]. From the erythro‐racemates 9, 11 , and 13 , the erythro,erythro/erythro,threo‐diastereoisomer mixtures 16 / 17, 20 / 21 , and 24 / 25 were obtained in ratios of 20 : 80 to 28 : 72 (HPLC), which were separated by chromatography. From the threo racemates 8, 10 , and 12 , the threo,threo/threo,erythro‐diastereoisomer mixtures were obtained in a ratio of ca. 25 : 75 (1H‐NMR). The relative configurations were assigned by means of 1H‐NMR data and X‐ray crystal‐structure determination of 21 . Hydrolysis of 21 afforded the diastereoisomerically pure N‐(benzyloxy)carbonyl derivative 27 of α‐amino‐β‐hydroxy‐γ‐methylpentanoic acid 26 , representative of the novel group of polysubstituted α‐amino‐β‐hydroxycarboxylic acids. 相似文献
19.
Qingfeng Pan Bruce C. Noll Anthony S. Serianni 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(2):o82-o85
Methyl β‐l ‐lactoside, C13H24O11, (II), is described by glycosidic torsion angles ϕ (O5Gal—C1Gal—O4Glc—C4Glc) and ψ (C1Gal—O1Gal—C4Glc—C5Glc) of 93.89 (13) and −127.43 (13)°, respectively, where the ring atom numbering conforms to the convention in which C1 is the anomeric C atom and C6 is the exocyclic hydroxymethyl (CH2OH) C atom in both residues (Gal is galactose and Glc is glucose). Substitution of l ‐Gal for d ‐Gal in the biologically relevant disaccharide, methyl β‐lactoside [Stenutz, Shang & Serianni (1999). Acta Cryst. C 55 , 1719–1721], (I), significantly alters the glycosidic linkage interface. In the crystal structure of (I), one inter‐residue (intramolecular) hydrogen bond is observed between atoms H3OGlc and O5Gal. In contrast, in the crystal structure of (II), inter‐residue hydrogen bonds are observed between atoms H6OGlc and O5Gal, H6OGlc and O6Gal, and H3OGlc and O2Gal, with H6OGlc serving as a donor with two intramolecular acceptors. 相似文献
20.
Magnus Frnbck Lars Eriksson Gran Widmalm 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(6):700-701
The structure of the title compound, C28H38O18S, has been determined. The torsion angles of the glycosidic linkage in the non‐reducing disaccharide, ?H and ?H′, have values of 3 and 53°, respectively. The latter torsion angle is in agreement with the exo‐anomeric effect, whereas the former shows an eclipsed conformation. Both glycopyranosyl residues adopt a slightly distorted chair conformation. 相似文献