Skeletal structure elucidation

There have been three reports of the same dimeric disulfide. It was first isolated from an unidentified sponge from Guam and the structure elucidated by analysis of spectral data. The (E,E) stereochemistry of the disulfide (500) was defined by comparing the I3C NMR spectroscopic data with those of the (E,Z)-isomer (501) that was obtained as an unstable minor product [425]. Compound 500 was isolated from a species of Psammaplysilla and was called psammaplin A [426]. It was also isolated from Thorectopsamma xana, collected from the same location in Guam, together with a minor dimeric metabolite bisaprasin (502). Both compounds inhibited growth of Staphylococcus aureus and Bacillus subtilis [427]. Psammaplin A (bisprasin) (500) was later isolated from a Dysidea species of sponge and shown to act on Ca2+-induced Ca2+ release channels of skeletal muscle [428]. 

Recent chemical studies on the soluble metabolites of the lower fungi and bacteria have revealed that 3-amino-3-deoxy sugars are often components thereof. Several closely related amino sugars have been reported. The stereochemistry of 3-amino-3-deoxy-D-ribose and 3-amino-3-deoxy-D-glu-cose66a have now been fully elucidated, and skeletal structures have been assigned (see Table II, p. 231) to the others, generally on the basis of periodate oxidation patterns. 

The 13C-NMR spectra of these compounds were analyzed to identify and distinguish skeletal features of the atisine and veatchine-type alkaloids for use in the structure elucidation of new C20-diterpenoid alkaloids. 

The alkali melt of lunarine gives, in addition to spermidine (87), the two biphenyl derivatives 92 and 93 (88). Although all but two carbon atoms of lunarine are accounted for by these results, a skeletal rearrangement has occurred during the formation of 92 from 91, which complicated the structural elucidation of this alkaloid [for discussion of this rearrangement, see Warnhof (89)]. 

ACD/Structure Elucidator has matured over the past 6 years to become the most capable commercial CASE system available today. The expert system has been described in detail in previous works." " The first generation system was developed for the elucidation of molecular structures of intermediate-sized organic molecules with 20-25 skeletal atoms using simple ID C NMR spectra. The second pubhcation" " reported on developments allowing the elucidation of structures of large molecules, typical of those found in the world of natural products, and utilizing mainly 2D NMR data as the source datasets. The application and success of the system as a powerful and versatile tool for the structure elucidation of complex chemical structures has been demonstrated in numerous works and will not be discussed in more detail in this review. " " ... 

Seourinine, the most abundant alkaloid of this group, was first isolated by Russian workers in 1956 but its structure was fully established only in 1962. In the subsequent years a variety of alkaloids of the same skeletal type (1) but differing in stereochemistry and minor functionality were isolated and characterized. More recently, three alkaloids possessing a lower homolog structmre (2) of the seourinine type were discovered. Table I lists the known alkaloids according to these two subgroups. Several alkaloids (phyllanthidine, suffruticodine, and suffruticonine) have not been structurally elucidated but their molecular formulas and spectral properties indicate most probably a securinine-type skeleton (Section II, L). 

Using degradative and synthetic sequences which had served so admirably in the structural elucidation of securinine, the Japanese workers were able to confirm fully (Scheme 26) 62) the basic skeletal structure proposed by Iketubosin and Mathieson. Reduetion with sodium borohydride gave dihydronorsecurinine (165) whose structure was evident from the IR (1820, 1750, 1640 cm ) and UV [214 (log e 4.16) mp] spectra. Furthermore, this compound was also isolated from the plant (Section III, C). Catalytic hydrogenation of 164 gave a mixture of the hydroxy ester 166 and the saturated lactone 167. The structure of compound 166 was assigned on the basis of spectral data. The presence of compound 167 was noted by an IR absorption at 1790 cm , but this compound could not be isolated since it was transformed upon chromatography into the hydroxy amino acid 168. 

Similar compounds can also be prepared by treatment of solutions of the Co(CO)4 anion with halogenated compounds. The skeletal structure of this class of compound was elucidated by chemical techniques (266) and shown to consist of a triangular cluster of cobalt atoms, each of... 

In the first section, alkaloids isolated from the Gelsemium species up to now are presented in tabular form, and the structure elucidation of the representative alkaloids using mainly spectroscopic methods are described. The second part of this chapter covers the biogenetic speculation of the structurally unique Gelsemium alkaloids as well as the biomimetic transformation of the known indole alkaloids leading to the various skeletal types of Gelsemium alkaloids. 

Alkaloids may be identified from their mass spectra and analyzed by GC/MS. Molecular ions and the characteristic ions of skeletal units may aid in structure elucidations. 

Katakawa K, Kitajima M, Aimi N, Seki H, Yamaguchi K, Furihata K, Harayama T, Takayama H (2005) Structure elucidation and synthesis of lycoposerramine-B, a novel oxime-containing Lycopodium alkaloid from Lycopodium serratum Thunb. J Org Chem 70 658-663 Inubushi Y, Ishii H, Yasui B, Hashimoto M, Harayama T (1966) Serratinine a novel skeletal Lycopodium alkaloid. Tetrahedron Lett 7 1537-1549... 

Phenyl alkyl sulfides undergo reactions typical of their counterpart ethers but show additional skeletal rearrangements that complicate structure elucidation. Elimination of 8H is common in compounds whose usual cleavage pathways are less facile. Aromatic disulfides often undergo additional losses of 83 and/or H82. 

The molecular structure of phosphetane (6) was elucidated by X-ray crystallographic analysis, as discussed in Section II.89 The preferred isomer is (6-(l 4) (2 6)), which is shown in two space orientations in order to illustrate the application of the Permutational Notation. The ligand indices are prescribed by the Sequence Rules.75 The ligand and skeletal indices must coincide in (6-E), which thus gives the orientation of the skeleton. The permutation (1 4) (2 5) gives isomer (6 -(l 4) (2 5)) as a... 

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