The first total synthesis of natural (-)-lankacidin C (1) has been achieved by a convergent, enantioselective sequence starting from D-arabinose and L-aspartic acid, proceeding through the tricyclic carbamate 15 as an advanced relay intermediate. Specifically, the p-lactam diene intermediate 41 is acylated by the thiopyridyl ester 34c. The resulting P-ketolactam 42 is stereospecifically reduced by KEt3BH to carbinol 43, which on desilylation undergoes acid-catalyzed N -0 acyl migration to yield the &lactone 44. The derived iodo aldehyde 46 undergoes Stille coupling to give tetraene 54a, which upon Stork-Takahashi cyclization to ketone 56 and CBS reduction gives the key relay 15. N-acylation of the latter, and then regioselective carbamate scission followed by Dess-Martin oxidation, produces the target antibiotic (-)-lankacidin C (1).

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The natural abundance 13C nmr spectra of the antibiotics tobramycin, kanamycin B, and their carbamates were recorded at several pHs. The chemical shifts of the four antibiotics, of nebramine, neamine, deoxystreptamine, and of the methyl 2-amino-, 3-amino-, and 6-amino-a-D-glucopyranosides, were assigned and the conformation of all compounds in water solution was determined.A mixture of aminoglycoside antibiotics3 whose main components are nebramycin factors 2, 4, and 5' is produced by Streptomyces tenebrarius. These substances have been shown to be apramycin4 and carba-mates5 of kanamycin B (lc)6 and of tobramycin (la).7 coupled spectra were sufficient for the 13C chemical shift assignments indicated in Table I. The spectral analysis of the tricyclic compounds was aided by the spectra of the amino monosaccharides methyl 2-amino-2-deoxy--D-glucopyranoside (2a), methyl 3-amino-3-deoxy-a-A 13C nmr spectral analysis of the carbamates and their hydrolysis products now was undertaken in order to discern the position of the carbamyl moiety and to lay the groundwork for structure analysis of aminoglycoside antibiotics by this new, diagnostically powerful research tool.8Natural abundance 13C nmr spectra of 0.3-0.5 M aqueous solutions of componds 1 and others (vide infra): containing 5% dioxane as internal reference, were recorded on a Fourier transform spectrometer operating at 15.08 MHz.10 Proton resonance de-(1) Carbon-13 Nuclear Magnetic Resonance Spectroscopy of Naturally Occurring Substances. XXV. For the preceding paper, see N. J.

Das Antibioticum Hygromycin B, eine Verbindung C20H37N3O13 aus Streptomyces hygroscopicus, wurde hydrolytisch gespalten und die Spaltprodukte charakterisiert und identifiziert. Die Kenntnis ihrer Struktur und die Interpretation von 13C‐NMR.– (CMR.)‐ Spektren führten zur Strukturaufklärung des Antibiotikums.