I. Pelczer

Stereochemical studies—75 : Saturated heterocycles—62. connection between the diastereoselectivity and the dominant conformation in the formation of condensed- skeleton 1,3-oxazines, first X-ray diffraction evidence of N-outside conformation

Abstract The rapid, spontaneous epimerization occurring at the C(2) chirality centre of a new diastereomeric (r-4,c-2,c-5)-2-(p-nitrophenyl)-3-methyl-4,5-tetramethylenetetrahydro-1,3-oxazine led to the conclusion that the configuration at C(2) of the bicyclic 1,3-oxazines formed by the cyclization of alicyclic 1,3-aminoalcohols with aldehydes is determined by the dominant conformation of the product. The first X-ray diffraction evidence is given for the N-outside conformation of compounds of this type.

Synthesis and NMR study of norbornane/norbornene-fused tetracyclic azetidinones

Abstract Tetracyclic azetidinones 8 , 9 and 12 – 17 were synthesized. In the cases of 8 and 9 , the main component was isolated from the two-component product of the cycloaddition. The minor component was concentrated to give a mixture, from which a computer technique utilizing the known spectrum of the main component gave the proton resonance spectrum also of the minor component. Only one diastereomer could be isolated for the each of the analogues 12 – 17 . Reaction of the 1,3-oxazine 3 with chloroacetyl chloride gave, besides the azetidinone 12 , the 1,3-oxazine [2,3- b ]-1,3-oxazin-4-one derivative 18 . Configurations and conformations were determined by IR, 1H and 13C NMR spectroscopy.

New sesquiterpene esters and alkaloids from Euonymus japonicus: the ‘Ejap’ series. X-Ray molecular structures of Ejap-2, -3, -4, -5, -6, and -10

Nine new sesquiterpenoid esters (Ejap-2, -3, -4, -6, -7, -10, -12, -13, and -14) have been isolated from Euonymus japonicus, besides a known compound (Ejap-5). Structures of the isolated substances were deduced from 1 D, as well as 2D COSY and NOESY, 1H n.m.r. and mass spectra. The position of the benzoyl groups among the other esterifying moieties was located by X-ray diffraction for Ejap-2, -3, -4, -5, -6, and -10. Among the sesquiterpene cores, 8-deoxypolyalcohol C, 8-epi-polyalcohol C, 9-epi-alcohol A, and 4,12-dideoxyeuonyminol have been obtained in neither a synthetic nor a natural product until now.

Stereospecific one-pot synthesis of a new 6,11-dioxa-7-aza-D-homosteroid ring system☆

Abstract ( r -7a, t -11a, c -13a)-6,7,7a,8,9,10,11,11a-Octahydro[1,3]benzoxazino [3,4- a ] [3,1] benzoxazine ( 3 ) was prepared in a one-pot synthesis from trans -2-hydroxymethylcyclohexylamine. 3 was epimerized to 4 ( r -7a, t -11a, t -13a), furnishing an equilibrium mixture with 3 : 4 = 2:1. The stereochemistry of the diastereomers was determined with via DRDS measurements.

Trimethylsilylated N-alkyl-substituted carbamates: III. Structure of trimethylsilyl-N,N-diisopropyl carbamate in solid phase and in solution☆

Abstract The conformers of trimethylsilyl- N , N -diisopropyl carbamate were studied by 1 H NMR spectroscopy. The barriers to rotation by isopropyl groups and to the rotation around the amide bond, and the population of the conformers were determined from the coalescence temperature of the methyne signal. Single crystal X-ray diffraction studies revealed that the crystal had formed from preferred conformer in solution. The mirror symmetric conformer is stabilized by an intramolecular CH ⋯ O hydrogen bond and by an intramolecular O ⋯ Si donor-acceptor interaction.

New sesquiterpene esters from Euonymus europaeus and E. latifolius

Ten new sesquiterpenoid esters based on the dihydroagarofuran moiety, viz.(16), (28), (29), (30a), (30b), (31), (32), (36), (37), and (40), have been isolated from Euonymus europaeus and E. latifolius in addition to three known compounds (10), (14), and (15). Structures of the isolated compounds were deduced from 1D and 2D COSY and NOESY 1H n.m.r. and mass spectral data.

Stereochemical studies. Part 78. Saturated heterocycles. Part 65. Synthesis and spectroscopic studies of cis-5,6-trimethylene-, and cis- and trans-5,6-tetra-and -pentamethylene-1,3-oxazinan-4-ones

N-Methyl-cis-5,6-trimethylene-, and cis- and trans-5,6-tetra- and -pentamethylene-1,3-oxazinan-4-one derivatives (15) and (16) were prepared by cyclisation, with aldehydes, of the appropriate alicyclic 2-hydroxy-1;-carboxamides. In each case, formation of the new C-2 centre of chirality was found to take place stereospecifically and only the (r-5,t-2,t-6) and (r-5,c-2,c-6) diastereoisomers, respectively, were formed. The conformations of the N-methyl-and N-unsubstituted cis-trimethylene-, cis-tetramethylene-, and cis-pentamethylene-1,3-oxazinan-4-ones (13)–(16) were determined by 1H and 13C n.m.r. spectroscopy in solution. Good agreement was obtained with the earlier data established by X-ray diffraction analysis of the crystalline substances. The relative steric structure of the C-2 centre of chirality was also proved by d.n.O.e. measurements. It was found that the substituent at position 2 did not affect the conformation significantly.

The composition of primycin

The macrolide antibiotic primycin is shown to consist of more than twenty compounds. Nine components, representing about 90 % of the total, have been isolated and their structures elucidated by spectroscopic methods. Molecular weights were determined by FAB mass spectrometry. The components studied belong to three groups (see Fig.), depending on substituent R2 and each set represents homologous series, differing in substituent R1. The structure proposed previously for primycin was unambiguously proved and assigned as that of the A1 component.

Three-dimensional correlation by combination of 2D NMR spectra

Abstract A method is proposed to make automatic structure elucidation and identification more reliable and unambiguous. Space correlation is utilized to map spin systems and to produce data banks on the basis of pattern recognition. The essence of the method presented is the mathematical combination of the measured 2D NMR spectra, but further extensions are also possible. From the correlation solid constructed in this way, the entire hidden information content of the individual 2D NMR spectra can be extracted.

Adenosine Cyclic 3′, 5′-Phosphoramidate and N,N-Dimethylphosphoramidate: Synthesis Via Symmetrical and Mixed Anhydrides and Hydrolysis

Abstract The title compounds were synthesized by converting cyclic AMP with a sulfonyl chloride to the symmetrical anhydride or with diphenyl phosphorochloridate to the mixed anhydride, then aminolyzing the anhydrides without isolation. The synthesis preferentially gave Sp-amides. Characteristic differences were observed in the behavior of the unsubstituted amide and the dimethylamide under hydrolysis conditions.