The structure of ptilomycalin A (1), a marine alkaloid possessing potent antiviral and antibiotic activites, has been determined on the basis of NMR analyses of its trifluoroacetyl (TFA) derivative (2). It has a unique structure consisting of a polycyclic guanidine and a spermidine group, each of which is linked to a 16-hydroxyhexadecanoic acid moiety. The rotational isomerism of the acylated sperimidine moiety of 2 has been studied by comparing the NMR properties of the synthetic trifluoroacetyl derivatives of spermidine (5), dipropylenetriamine (11), diethylenetriamine (12), and pentylamine (13). From these experiments, a plausible conformation of 2 and ptilomycalin A (1) has been proposed as shown in 2c, in which an anion is trapped between the guanidine and spermidine moieties. The TFA derivative 2 acts as a phase-transfer agent. NMR analysis of the stability of the complexes formed between 2 and several organic carboxylates in CDC13 solutions has been carried out.

Low-frequency RR spectra, showing 34S shifts of bands having Mo-S stretching character in oxidized (top) and reduced (bottom) DR.Excitation at 720.8 nm produces stronger enhancement for DRox, although the same features can be seen with 676.4-nm excitation. The spectrum of DRox was obtained by 180" backscattering from a frozen solution mounted on a cold finger cooled to 77 K. The 720.8-nm excitation line was provided by an Ar* pumped dye laser (Pyridine 2). The scattered light was collected with a Spex Triplemate equipped with a C C D (Photometrics). Conditions: 100-mW output laser power. The spectrum of DRred was obtained as described in Figure 2. Peaks marked with an asterisk are due to ice (228 cm-I) or laser plasma lines (304 cm-I). The 34S-containing protein was obtained from Rb. sphaeroides grown on 34S. j4S, 90 atom %, obtained from Isotec, Inc., as elemental S was converted to (NH4)234S04 by boiling in a 3:1 mixture of HCI and HNO, in an oil bath at 170 "C until no more yellow fumes were seen. The solution was neutralized with N H 4 0 H and dried. Cultures of Rb. sphaeroides were grown for three generations on sulfate-free medium to deplete endogenous sulfur. The culture was then transferred to 34S04containing medium for growth and isolation of 34S-enriched DR.(14) (a) Cramer, S. P.; Hille, R.

Three metabolites of fucoxanthin were isolated from a brown alga, Scytosiphon lomentaria, and the structure of a new compound was determined by NMR.The content of fucoxanthin, a biologically active carotenoid, in four edible brown algae, cultivated in deep seawater, was studied.

The structures of sargaquinoic acid and sargaquinal, new plastoquinones isolated from the brown alga Sargassum serratifolium, were elucidated as 1a and 2.

A concise, highly convergent total synthesis of saptomycin B, a member of the pluramycin class of antitumor antibiotics, is reported. The target compound was assembled from four building blocks (a tricyclic platform, two sugars, and an alkynal) in 15% yield through 10 synthetic operations. The key steps included the regioselective installation of two amino sugars (L-vancosamine and D-angolosamine) on the tricycle and the efficient construction of the tetracyclic skeleton by an aldol reaction followed by formation of the pyranone. The unknown configuration at C14 was assigned as R.