Coupling constants lactones

Proton Coupling-Constants of Methyl fi- (25) and a-D-Glucofuranosidurono-6,3-lactone (26), and l,2-0-Isopropylidene-a-D-glucofuranurono-6,3-lactone (33)... 

Trisubstituted lactones, e.g., 1, have also been discussed500 and diagnostic 1H and 13C chemical shifts and H. H coupling constants were collected501 to assign diastereomeric lactones of type 2. 

A novel cysteine derivative, spongiacysteine, was isolated recently from marine sponge. It was converted to lactone 4 by reaction with 2,4,6-trichlorobenzoyl chloride, 4-dimethylaminopyridine (DMAP), and triethylamine. Selected nuclear Overhauser enhancement spectroscopy (NOESY) correlation and coupling constants are given <2004CL1262>. 

The carbonyl frequency in the infrared spectrum provides a fairly characteristic method for differentiating between 1,4- and 1,5-lactones of aldonic acids. With few exceptions, the absorptions are in the range 1790-1765 and 1760 to 1725 cm-1, respectively.69 Configurational and conformational conclusions have been drawn from H and 13C NMR spectroscopy of aldonic acids and aldonolactones, using different correlation methods, enriched compounds, and shift reagents. For example, the solution conformation of aldono-1,4-lactones enriched with 13C at C-l have been determined on the basis of the coupling constants (homo and heteronuclear). In general, 0-2 is oriented quasi-equatorially due to stereoelectronic factors.36 Similar conclusions were made by Horton and Walaszek, who described the conformation of pentono- 1,4-lactones as an equilibrium between the 3E and forms.70 Conformations of D-hexono-1,4-lactones in solution have also been studied by NMR spectroscopy.70a The solution equilibrium of protected derivatives and their conformations have been described.71... 

The stereochemistry of the /1-lactone 2 (R = CH3) is confirmed by carbon halogen bond cleavage with tributyltin hydride which provides the tram-3,4-dimethyl-/J-lactone 3 (R = CH3) in 89% yield. The coupling constant between methine protons on the ring is 3.9 Hz, in agreement with a trans disubstitution5. 

In addition the cis relationship is exclusively observed in the formation of these bicyclic lactones, owing to attack of the hydroxy function at C-l on the conformer in which the hydroxy group at C-3 lies in the plane of the double bond. All products show a characteristic carbonyl absorption at —1770 cm-1 in their IR spectra, and a cis H-2-H-3 coupling constant of 4-5 Hz44. 

The racemic lactone ( )-18 was obtained as a pure and crystalline compound, and its relative stereochemistry had to be determined. I thought, in 1960, XH NMR analysis to be the most appropriate method to solve the problem, because it had already been known to use a vicinal coupling constant for the stereochemical studies of cyclohexane compounds including terpenoids and steroids. Figures 1.13(a) and (b)... 

The location of the substituents was determined from a HMBC experiment. According to this data, the acetoxy group was located at C-3, the double bond between C-l 1 and C-12 and the lactone ring between C-13 and C-20. The relative stereochemistry of the acetoxyl were determined based on the coupling constant of the geminal proton and the data from the NOESY spectrum. The relative stereochemistry of the lactone group was determined also based from a NOESY experiment. According to those facts, the structure of (34) is showed below, Fig. (23). 

Scheme 15). Treatment of 42 with DDQ in CH2CI2/H2O (19/1) afforded diol 43 in 81% yield. Subsequent oxidation was carried out with a catalytic amount of tetrapropylammonium perruthenate (TPAP) and N-methylmorpholine-Y-oxide to furnish lactone 44 in 82% yield.In the H NMR spectrum of 44, the coupling constants of Jl,l-trans, and... 

Analysis of the nmr coupling constant data for d(TpG) and d(TpL) indicates that there are no major conformational differences between the two nucleotides and may suggest why lactone lesions are, in some cases, resistant to repair. 

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