Water molecules confined inside narrow pores are of great importance in understanding the structure, stability, and function of water channels. Here we report that besides the H-bonding water that structures the pore, the permanent presence of a significant, fast-moving fraction of incompletely H-bonded water molecules inside the pore should control the free entry and exit of water. This is achieved by means of complementary DSC and solid-state NMR studies. We also present compelling evidence from X-ray diffraction data that the cluster formed by six water molecules in the most stable cage-like structure is sufficiently hydrophobic to be stably adsorbed in a nonpolar environment.

Six dihydro-P-agarofuran [5,11 -epoxy-5P,1 O~-eudesm-4(14) -ene] sesquiterpenes with a novel substitution pattern were isolated from Maytenus magellanica and their structures were elucidated by means of l H and 13C NMR spectroscopic studies, including lH-13C heteronuclear correlation (H ETCOR), long range correlation spectra with inverse detection ( H M BC) and NOE experiments. Their absolute configurations were determined by application of the CD exciton chirality method while hydrolysis and preparation of derivatives provided additional information. One of the sesquiterpenes exhibited sign if icant antif eeda nt activity against Spoduptera littoralis.As part of an intensive course of research into biologically active metabolites from Celastraceae species used in folk medicine, '-' Maytenus magellanica Hook was studied. This species grows in the phytogeographical region of the Antarctic forest (Argentina and Chile) and had shown moderate activity (LCs0 650 ppm) in the brine shrimp lethality b i ~a s s a y . ~Compound 1 showed antifeedant activity against Spodoptera littoralis in an election test, although it was not particularly effective against microorganisms 6*t or viruses.$The six metabolites isolated displayed a hitherto unreported substitution pattern on a dihydro-P-agarofuran [5,l l-epoxy-5~,lO~-eudesm-4( 14)ene] skeleton with la, 2p, 3P, 4p and 9P substituents. Four of the compounds also had substituents at 6p. The compounds closest in structure to them are those isolated by Kupchan from other Celastraceae: maytolin and maytolidin, with the basic polyhydroxy skeleton of maytol (la,2a,3P,4P,6P,9~,15-heptahydroxydihydro-P-agarofuran); they are also related to the sesquiterpene core of the macrocyclic alkaloids evonino1,8 euonyminol and isoeuonyminol. 'Regrettably, the absolute configurations of dihydro-p-agarofuran sesquiterpenes have not been reported. Clardy,' applying X-ray diffraction techniques to a celorbicol derivative with a heavy atom, gave the absolute configuration of a series of celorbicol derivatives; contradictory results were published regarding the determination of the absolute configuration of malkanguniol l 2 although the later corrections l 3 agreed in the main with the findings of Clardy. This paper gives an account of the structural elucidation of compounds 1, 4, 7, 9, 10 and 11 and their absolute configuration based on C D techniques and chemical correlations (Schemes 1 and 2). DiscussionThe molecular formula of compound 1 [u]k0 + 18.0 lo-' deg TCompound 1 was assayed on Staphylococcus aureus ATCC 6538, Bacillus subtilis CECT 39, Escherichia coli CECT 99, Salmonella sp. CECT 456, Saccharomyces cerevisiae X 2180 A, Candida albicans and Pseudomonas aeruginosa (from the Dept. of Microbiology of the University of Vancouver, BC). $ Herpes simplex virus Type 1, KOS strain (HSV-l), Vesicular Stomatitis Virus, Indiana strain (VSV) and HeLa (uterus neck cancer) cells were used.

Figure1.(a) Tr ipeptides found by Wennemers and co-workers.( b) Dipeptides designed based on pyranoid sugar e-a nd z-amino acids.

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The first example of a regioselective and organocatalyzed 1,3-dipolar cycloaddition reaction between conjugated alkynoates and nitrones "on water" is described.