Modified Mosher’s method

The absolute stereochemistry of isosaraine-1 (48) and -2 (49) has been established using the modified Mosher s method on the reduced derivatives 50 and 51 obtained after reaction of the natural products with NaBH4 [31]. 

The stereochemistry of each enantiomer separated by the chiral HPLC has been studied after methanolysis of the epoxy ring. Examining the H NMR data of esters of the produced methoxyalcohols with (S)- and (R)-a-methoxy-a-(tri-fluoromethyl) phenylacetic acid by a modified Mosher s method [181], it has been indicated that the earlier eluting parent epoxides are (3S,4R)-, (6S,7R)-, and (9R,10S)-isomers (Table 7) [75, 76, 179]. The above three chiral HPLC columns show different resolution abilities but a different elution order is not observed. The resolution profile by the reversed-phase OJ-R column has been generalized with molecular shapes of the epoxy compounds considering the... 

Yessotoxin (214) is a polyether from the scallop Patinopecten yessoensis and has been implicated in diarrhetic shellfish poisoning (DSP). The structure and partial stereochemistry of yessotoxin were deduced from spectral data [219]. The relative stereochemistry of yessotoxin and the structures of two new analogues, 45-hydroxyyessotoxin (215) and 45,46,47-trinoryessotoxin (216) were also established [220]. The absolute stereochemistry of yessotoxin (214) was determined by NMR spectroscopy using a chiral anisotropic reagent [221]. The absolute configuration at C45 in 45-hydroxyyessotoxin (215), isolated from P. yessoensis, was determined by the use of a modified Mosher s method [222]. 

Rezanka analysed the fatty acid composition of several species of myxomycetes. In addition to the common fatty acids, polyunsaturated and methylene non-interrupted polyunsaturated fatty acids, for example, with 5, 9- and/or 5, 11-double bonds, were identified by GS-mass spectrometry of their corresponding oxazolines [25]. Multibranched polyunsaturated fatty acid and its four glycosides (50 -54) were isolated from seven different myxomycetes [26]. The absolute configurations of hydroxyl groups were determined by modified Mosher s method, and the glycosides were revealed to contain glucose, mannose, and rhamnose. It may be interesting that these fatty acid constituents contained by the seven species of myxomycetes were different (Table 1). 

The synthesis was achieved from commercially available (+)-2, 3-0-isopropylidene-L-threitol in 26 steps. The key steps are the stereoselective construction of a chloroolefin unit [step f in Scheme (2)] and the intramolecular Reformatsky-type reaction [step g in Scheme (3)]. Because the stereochemistry of C3, Cll, C13 and C14 in synthetic 8 was undoubtedly constructed to be all S by the organic synthetic method, the absolute stereochemistries of C3, Cll, Cl3 and C14 in natural 2 were determined to be R, R, R and R. On the other hand, since the absolute stereochemistry of CIS in natural 2 was determined to be R by the modified Mosher s method, the total absolute stereochemistry of haterumalide NA (2) was revealed, which revised the previously reported structure [8]. To confirm these results, 8 was converted into the (i )-MTPA ester, which was the enantiomer of the (5)-MTPA ester of the natural haterumalide NA methylester on comparison of their H NMR spectra. 

Since zamamistatin (17) was an optically active alcohol with a C2 symmetrical structure, the absolute stereochemistry was determined using the modified Mosher s method [7]. The diol 17 was transformed into the (R)- and (iS)-MTPA esters. The calculated values ppm)... 

The absolute stereochemistry of 20 was determined using the modified Mosher s method [7]. Reduction of 20 with LiAlELt followed by TBDPSCl (tert-butyldiphenylsilyl chloride)/imidazole gave TBDPS ether 20A, Fig. (16). Treatment of 20A with (K)- and (5)-MTPACl gave (R)-and (5)-MTPA esters, 20B and 20C, respectively. The results, as shown in Fig. (16), established that the configuration at C3 was 35. Therefore, the absolute stereochemistry of haterumadioxin A (20) was determined to be 35, 6R and 8i . 

Amphidinolide Q (16), C21H34O4, is a 12-membered macrolide possessing four branched methyl groups, an a ti-methylene, and a ketone carbonyl, isolated from the marine dinoflagellate Amphidinium sp. (strain Y-5). The relative stereochemistry of amphidinolide Q (l) was elucidated on the basis of -based configuration analysis method and NOESY correlations. The absolute configurations of amphidinolide (16) were concluded to he AR, 7R, 9S, 115, and 135 by application of the modified Mosher s method to amphidinolide 0 (16) and the linear methyl ester derivatives of amphidinolide... 

INADEQUATE spectrum. The absolute configurations at C-11, C-12, and C-14 were elucidated by combination of the y-based configuration analysis and the modified Mosher s method. Originally, the absolute configuration at C-6 was proposed to be S on the basis of H NMR data of 6,11,12-rm-MTPA esters of C-... 

G. to V j that produces ciguatoxin precursors (142—147) and maitotoxin (148). The absolute stereochemistry of gambieric acids A-D (149-152) were assigned by the modified Mosher s method, conformational analysis based on J values and NOE correlations, chiral fluorimetric HPLC analysis, and synthesis of A/B-ring models of gambieric acids A-D (149-152). ... 

Assignment modified Mosher s method Revision rationale total synthesis Remaining undefined none... 

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