HOHAHA spectrum

The HOHAHA spectrum (100 ms) of podophyllotoxin is presented. The HOHAHA, or TOCSY (total correlation spectroscopy), spectrum (100 ms) shows coupling interactions of all protons within a spin network, irrespective of whether they are directly coupled to one another or not. As in COSY spectra, peaks on the diagonal are ignored as they arise due to magnetization that is not modulated by coupling interactions. Podophyllotoxin has only one large spin system, extending from the C-1 proton to the C4 and 015 protons. Identify all homonuclear correlations of protons within this spin system based on the crosspeaks in the spectrum. 

The HOHAHA spectrum (100 ms) of vasicinone is shown. Interpret the spectrum, and determine the different spin systems from the crosspeaks in the spectrum. 

Fig. (2). The HOHAHA spectrum (tm = 150 ms) for the sugar moiety of saponarioside C from Saponaria officinalis showing the sub-spectra corresponding to each anomeric proton. Note that for the glucose (G, G G") and xylose (X) units, the correlations were observed from the anomeric protons till terminals. However, the correlation stopped at H-4 of the galactose (G" ) moiety due to the small coupling between H-4 and H-5. Spectrum measured at 500 MHz in pyridine-. ...

Fig. 2. H ID and 2D-HOHAHA spectra of PHA isolated from P. putida cultivated on linoleic acid. The numbers in the specu-a refer to the corresponding protons in the two assigned structures. Crosspeaks between protons are indicated with two numbers. For the 2D-HOHAHA spectrum (Bax and Davis, 1985) 512 experiments of 2048 data points, using an isotropic mixing time of 80 ms, wete recorded on a Bruker AMX 400 wb NMR spectrometer. 

Figure 3 shows the S3-CH2 signal is split in the proton dimension into two peaks centered at 3.7 and 4.0 ppm. The former peak overlaps the S2-CH2 peak in the lower resolution HOHAHA spectrum shown in Figure 4. As a result, relative positional DS values calculated from the HOHAHA spectrum would be low for C3 and high for C2. This work shows that 2-D NMR analysis of intact EC can provide structural information on polymer substitution, but not quantitative data on positional DS without substantially more effort to resolve peak overlaps spectroscopically or by deconvolution of overlapping 2-D peak volumes.

Like die calculation of the relative DS made for the intact polymer, the relative positional DS of the TFA-hydrolyzed EC can also be calculated from the cross peaks on HOHAHA spectrum (Figure 6). The relative positional DS values are listed in Table 2. Because of the improved spectral resolution of the hydrolyzed EC relative to the intact EC, there are no signal overlaps for the sidechain methylene protons and the calculated values are almost the same as those determined by GC-mass spectrometry and ID " C NMR analyses on the acid hydrolysate. However, since the C NMR method provides an absolute rather than relative positional DS value, it is still the me od of choice for EC characterization. 

Figure 6 A section of cross peaks in the HOHAHA spectrum of the ethyl cellulose hydrolysate...

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