Structures of minor components of the validamycin complex.
complicated oligosaccharides using NMRspectroscopy have developed quite remarkably. The structure of validamycin G (VM-G),43 the most recently discovered congener was established by making use of these techniques. Wehave now used NMRto reinvestigated the position of the glycosidic linkage of the minor components which had remained obscure. The results were first disclosed in a patent application,53 though without experimental data. Here we discussed the structures of the minor components with experimental results. To elucidate the unidentified positions of the glucosidic linkage by *H NMRspectroscopy, VM-B~ F were acetylated with acetic anhydride and pyridine to give the corresponding peracetyl derivatives. The chemical shifts of 1-H and l'-H of the peracetates, recognized in the region of 3.2~3.6 ppm, indicate that the imino group is not acetylated. Therefore, these peracetates must be dodeca-O-acetyl validamycin B (Ac-
Synthetic studies on antibiotic validamycins. Part 14. Total synthesis of (+)-validamycins C, D and F
(+)-Validamycins C and F were first completely synthesised by use of a common blocked derivative 5 of (+)-validoxylamine A. The diols 6 and 7, obtained by acid hydrolysis of 5, were appropriately protected to give the aglycones 17, 25 and 30, which were condensed with glycosyl donor 11 or 19 to afford the condensates 20 and 26, being convertible, by deprotection and acetylation, to the totally O-acetylated derivates 21 and 33 of validamycins C and F, respectively. In addition, (+)-validamycin D was first synthesised by α-glycosylation of the protected derivative 37 of validoxylamine A.
Two new organic reference materials for delta13C and delta15N measurements and a new value for the delta13C of NBS 22 oil.
Analytical grade L-glutamic acid is chemically stable and has a C/N mole ratio of 5, which is close to that of many of natural biological materials, such as blood and animal tissue. Two L-glutamic acid reference materials with substantially different 13C and 15N abundances have been prepared for use as organic reference materials for C and N isotopic measurements. USGS40 is analytical grade L-glutamic acid and has a delta13C value of -26.24 per thousand relative to VPDB and a delta15N value of -4.52 per thousand relative to N2 in air. USGS41 was prepared by dissolving analytical grade L-glutamic acid with L-glutamic acid enriched in 13C and 15N. USGS41 has a delta13C value of +37.76 per thousand and a delta15N value of +47.57 per thousand. The delta13C and delta15N values of both materials were measured against the international reference materials NBS 19 calcium carbonate (delta13C=+1.95 per thousand ), L-SVEC lithium carbonate (delta13C=-46.48 per thousand ), IAEA-N-1 ammonium sulfate (delta15N=0.43 per thousand ), and USGS32 potassium nitrate (delta15N=180 per thousand ) by on-line combustion continuous-flow and off-line dual-inlet isotope-ratio mass spectrometry. Both USGS40 and USGS41 are isotopically homogeneous; reproducibility of delta13C is better than 0.13 per thousand, and that of delta15N is better than 0.13 per thousand in 100-microg amounts. These two isotopic reference materials can be used for (i) calibrating local laboratory reference materials, and (ii) quantifying drift with time, mass-dependent fractionations, and isotope-ratio-scale contraction in the isotopic analysis of various biological materials. Isotopic results presented in this paper yield a delta13C value for NBS 22 oil of -29.91 per thousand, in contrast to the commonly accepted value of -29.78 per thousand for which off-line blank corrections probably have not been quantified satisfactorily.