Conformational analysis by nuclear magnetic resonance. Nitrogen-15 and carbon-13 spectra of lactams

Phytochemical investigation of aerial parts of Woodsia ilvensis and its plasmin-inhibitory activity in vitro

The fern plant Woodsia ilvensis (L.) R. Br. belongs to the Woodsiaceae family and its leaves are used to treat diarrhea, soft-tissue injuries, and external injuries. Investigations of the compounds obtained from the plasmin-inhibitory-active extracts of W. ilvensis led to the isolation of two undescribed maleimide N-glycosides, an undescribed stilbenoid glycoside, and five undescribed acetylated flavonol bisdesmosides, together with 19 known compounds. The chemical structures of the isolated compounds were determined using spectroscopy. The absolute configurations of the sugar moieties were determined via HPLC after acid hydrolysis. Among the isolated compounds, some flavonoids and stilbenoid glycosides exhibited plasmin-inhibitory activity.

Amide nitrogen pyramidalization changes lactam amide spinning

Although cis-trans lactam amide rotation is fundamentally important, it has been little studied, except for a report on peptide-based lactams. Here, we find a consistent relationship between the lactam amide cis/trans ratios and the rotation rates between the trans and cis lactam amides upon the lactam chain length of the stapling side-chain of two 7-azabicyclo[2.2.1]heptane bicyclic units, linked through a non-planar amide bond. That is, as the chain length increased, the rotational rate of trans to cis lactam amide was decreased, and consequently the trans ratio was increased. This chain length-dependency of the lactam amide isomerization and our simulation studies support the idea that the present lactam amides can spin through 360 degrees as in open-chain amides, due to the occurrence of nitrogen pyramidalization. The tilting direction of the pyramidal amide nitrogen atom of the bicyclic systems is synchronized with the direction of the semicircle-rotation of the amide.

Cis-trans lactam amide rotation is a fundamental process and its understanding might aid molecular design. Here, the authors report the synthesis and study of bicyclic lactams which undergo spin through 360 degrees as in open-chain amides, due to the occurrence of nitrogen pyramidalization.

A theoretical and NMR lanthanide-induced shift (LIS) investigation of the conformations of lactams

Molecular mechanics (MM) with MMFF94 and MMX force fields and ab initio (RHF/6-31G*,RHF/6-311G**, and B3LYP/6-311G**) calculations are used with lanthanide-induced shift (LIS) to investigate the conformations of N-methyl-2-pyrrolidone 1, N-methyl-2-piperidone 2, ε-caprolactam 3, γ-valerolactam (1,5-dimethyl-2-pyrrolidone) 4, 2-azetidinone 5, 4-methyl azetidinone 6, 4-phenyl azetidinone 7, and N-methyl-4-phenyl azetidinone 8. The Yb(fod)₃ paramagnetic induced shifts of all the ¹ H and ¹³ C nuclei are measured and the corresponding diamagnetic complexation shifts obtained by the addition of Lu(fod)₃ . The complexation model (two-, three-, or four-site) used depends on the relative rates of the processes involved. The amide inversion is the same order as that of the 5- and 6-membered lactam rings and much faster than the lanthanide complexation and the inversion of the 7-membered ring. Both MM and ab initio calculations give an envelope conformation for 1 with C-4 out of the ring plane in agreement with the LIS analysis. For the piperidone ring of 2, the half-chair is calculated as the most stable form. The LIS analysis confirms this but cannot exclude a small amount (<2%) of the boat conformation. For 3, the LIS analysis gives a minimum for 90:10% chair to boat conformation, and 4 exists in two envelope conformations with the C₅ -Me ps-eq and ps-ax in an eq/ax ratio of 94:6%. In 2-azetidinone 5, the ab initio calculations gave both ring and nitrogen planar, but the MMFF94 calculations give a butterfly ring and pyramidal nitrogen. The LIS analysis for 5 gave good agreement (Rcryst 0.46%) for the MMFF94 geometry with endo NH but the planar ab initio geometries worse agreement (Rcryst = 1.1%). For 4-methyl-2-azetidinone 6, the MMFF94 geometry gave good agreement (Rcryst 0.96%) with two butterfly conformations with axial and equatorial methyl groups in 1:1 ratio. All the planar geometries gave worse agreement (Rcryst >1.5%). In 4-phenyl azetidinone 7, the MMFF94 geometry with 60% of the axial conformer gave Rcryst 1.2% but the other geometries Rcryst >1.5%. In contrast the N-methyl-4-phenyl-2-azetidinone 8 gave good agreement for all the geometries. The butterfly conformation gave Rcryst 1.1% for 80% of the axial conformer and the planar geometries Rcryst 0.98%. The LIS results confirm the ab initio and MM optimised geometries, but the conformer energies at times differ from the calculated values. They also differ considerably from the corresponding values for the lactones studied previously, and possible reasons for this are discussed.

The Oxeatamides: nitrogenous spongian diterpenes from the New Zealand marine sponge Darwinella oxeata

As part of our ongoing search for novel and bioactive compounds from New Zealand marine organisms, we investigated the extracts of the sponge Darwinella oxeata. NMR-guided fractionation led to the isolation of nine new nitrogenous spongian diterpenes, oxeatamide A (1), iso-oxeatamide A (2), oxeatamides B-G (3-8), and oxeatamide A 23-methyl ester (9), as well as two known compounds, membranolides C and D (10, 11).

The acid-mediated ring opening reactions of α-aryl-lactams

4-Aryl-azetidin-2-ones (β-lactams) undergo ring opening with triflic acid to give cinnamamides which, in benzene, react further to give 3-aryl-3-phenyl-propionamides. Prolonged reaction times in benzene give 3,3-diphenyl-propionamide via an aryl/phenyl exchange. Lactams of ring size 7 and higher also ring open, but only 7- and 8-membered rings give pure diphenylalkylamides. AlCl(3) only ring opens the 4-aryl-azetidinones.

Thermally induced dissociation nature of pure 2-pyrrolidinone via near-infrared correlation spectroscopy analysis

The temperature-dependent dissociation behavior of 2-pyrrolidinone in the pure liquid state was investigated via perturbation-correlation moving-window two-dimensional (PCMW2D) correlation spectroscopy and two-dimensional near-infrared (2D-NIR) correlation spectroscopy. Absorption bands in the region of 6900-6000 cm(-1) assigned to the first overtones of stretching modes of NH groups provided detailed information about the dissociation process from 25 degrees C to 95 degrees C. On the basis of PCMW2D analysis, the sequence of dissociation events occurring during the temperature variation were elucidated in two temperature ranges (25-60 degrees C and 65-95 degrees C). Specific dissociation order of the hydrogen bond under temperature perturbation was disclosed by 2D-NIR correlation spectroscopy. As temperature increased, the dissociation of larger oligomers occurred firstly with the generation of smaller oligomers, which were then consumed later by the decomposition of hydrogen bonds. The dissociation of stable cyclic dimers occurred mainly at higher temperature through gradually weakened hydrogen-bonding of NH groups.

Meehanines A-K, spermidine alkaloidal glycosides from Meehania urticifolia

From the whole plant of Meehania urticifolia, 11 new spermidine alkaloidal glycosides, meehanines A-K (1-11), were isolated. The structures of these new compounds were elucidated on the basis of the results of spectroscopic data analysis.

N-substituent effect on the cis-trans geometry of nine-membered lactams

The cis-trans geometry of a nine-membered lactam significantly depends on the N-substituents; N-acyl-1-aza-2-cyclononanones (1a-c) exist as cis form; in contrast, N-Z- 1-aza-2-cyclononanone (1d) exists as trans form both in the crystal and in solution.

Separation and characterisation of caprolactam-formaldehyde reaction products

Methylolation and condensation products formed in caprolactam-formaldehyde reaction mixtures have been identified using nuclear magnetic resonance (NMR) and mass spectrometry (MS). Previously unreported side-products were also detected. All of the reaction products were separated by micellar electrokinetic chromatography (MEKC) and high performance liquid chromatography (HPLC), and the separation parameters, such as efficiency and distribution constants, obtained in the two techniques were compared. For quantification, the response factors for the monomers were determined using standard calibration and hydrolysis, whilst those for the condensation products were deduced from the values of the monomers. The accurate determination of the response factors was confirmed by checking the mass balance of a known mixture.