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(2S,4S)-4-Hydroxyarginine is an intermediate in the biosynthesis of anatoxin-a(s) from L-arginine.

(–)-Bis-(3-acetoxyundec-5-enyl) disulphide and S-(–)-3-acetoxyundec-5-enyl thioacetate are two new sulphur compounds from Hawaiian Dictyopteris and may be precursors to undeca-1,3,5-trienes found in the essential oil.

Summary S-(3-Oxoundecyl) thioacetate (VIII), bis-(3-oxo-undecyl) disulphide (XII), (–)-3-hexyl-4,5-dithiacyclo-heptanone (XIII), and S-(trans-3-oxoundec-4-enyl) thioacetate (XIV) are four new lipids containing sulphur from Dictyopteris.

Circular dichroism spectra of the optically active cyclopropane hydrocarbons (1a) and (2), measured over a range of temperatures, showed these compounds to be configurationally identical. The c.d. spectrum was found to consist of two overlapping exciton pairs, corresponding to an equilibrium mixture of two solution conformers, for which thermodynamic parameters were calculated.Optical calculations using the excition model were used to obtain the sign of the rotational strength for the long wavelength part of the exciton pair for different conformers. The result confirmed the absolute (R,R) configuration for (1a) obtained from oxidative degradation, and the conformational assignment made from spectral analysis showing that the trans,trans-conformer is responsible for the pair of excition bands at shorter wavelength region. Both CNDO/2 and ab initio calculations confirmed that this conformer was of the lowest energy.

(3S)-cis-Octa-1,5-dien-3-ol, a possible precursor of the sperm-attracting substance, fucoserratene, produced by the female gametes of the brown alga Fucus serratus, is a minor constituent in the essential oil of the red seaweed Chondrococcus hornemanni.

(+)-(R)-4-Butylcyclohepta-2,6-dienone and (+)-6-butylcyclohepta-2,4-dienone are minor constituents of the essential oil of two species of Hawaiian Dictyopteris.

Nitration of 2,3-dimethoxynaphthalene leads to three mononitro-products, one dinitro-product, and one 1,2-naphthaquinone. Structural assignments, based largely on spectral data, differ in part from those in the literature.

Des-N-morphinan and des-N-isomorphinan derivatives can be differentiated by mass spectrometry or n.m.r. spectroscopy.