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Figure 11.64

two-bond correlations. Thus from h24, h25, and h26 the fragment shown in Figure 11.65 can be deduced from the HMBC correlations, which are shown as arrows.

Many of the aliphatic fragments are now connected to this olefinic/aromatic portion, including the h13 (CH3) fragment and the quaternary carbon c19 shared by h1 (CH3) and h2 (CH3). The important methyl ether fragment identified from h3 (CH3) is connected, and the correlation from h3 to c32 is particularly interesting since the chemical shift of c32 (196.0 ppm) is typical for a ketone carbonyl group. Comparison with Pristimerin, using co2ch

Figure 11.66
Figure 11.67

the h24, h25, h26 system for alignment, shows that this same carbon (C-3 of Pristimerin numbering) is bonded to a phenolic OH group. Thus, it appears that the C-3-C-4 double bond of Pristimerin has undergone addition of methanol and oxidation to the C-3 ketone (Fig. 11.66). If this were the only change between Pristimerin and LGJC3, the mass would increase by 30 mass units (methanol = 32, oxidation removes H2). In fact, the mass spectrum of LGJC3 does show m/z 494 as the parent ion, 30 mass units heavier than the nominal mass of Pristimerin (C30H40O4 = 464 Daltons). Thus, we can complete the structure of LGJC3 by inserting c31 (the only fragment not accounted for so far) as an a,p unsaturated ketone carbonyl (182.0 ppm) between c25 and c32 (Fig. 11.67). The ROESY spectrum (Fig. 11.68) confirms the location of h25 close to h11a and h11b and h24 close to h4a and h4b (Fig. 11.67). The crosspeaks are negative relative to the positive diagonal (negative NOE). The presence of correlations to both members of a geminal pair is a good confirmation of an NOE assignment.

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