Eduardo G. Gros

Methylation of carbohydrates bearing base-labile substituents, with diazomethane-boron triflouride etherate. I

Abstract Various tetra- O -acetyl- D -hexopyranoses were known to undergo acetyl migration upon methylation with Purdies reagents; thus, 1,2,3,4-tetra- O -acetyl-β- D -glucopyranose, 1,2,3,6-tetra- O -acetyl-β- D -glucopyranose, and 1,3,4,6-tetra- O -acetyl-β- D -glucopyranose and its α anomer are converted into methyl 2,3,4,6-tetra- O -acetyl-β- D -glucopyranoside when methylated with methyl iodide and silver oxide. It is now found that, when each of the above compounds is treated with diazomethane-boron trifluoride etherate, the methylated product is produced in high yield, with the methyl ether group in the expected position. Under the same conditions, 1,3,4,6-tetra- O -α- D -galactopyranose is converted into the 2-methyl ether without the acetyl migration which had been observed when the tetra- O -acetyl- D -galactopyranose was methylated with Purdies reagents. The tetra- O -acetyl- O -methyl- D -hexopyranoses were then transformed by deacetylation into the following mono- O -methylhexoses: 2- O -methyl-β- D -glucose, 4- O -methyl- D -glucose, 6- O -methyl-α- D -glucose, and 2- O -methyl-β- D -galactose.

Synthesis and bioactivity evaluation of brassinosteroid analogs

Four new analogs of 28-homocastasterone have been synthesized and completely characterized for the first time from stigmasterol. (22R, 23R,24S)-3beta-acetoxy-22,23-dihydroxy-5alpha-stigmastan+ ++-6-one (17), (22R,23R,24S)-3beta-bromo-22,23-dihydroxy-5alpha-stigmast an-6-one (18), (22R,23R,24S)-3beta-acetoxy-5,22, 23-trihydroxy-5alpha-stigmastan-6-one (20), and (22R,23R, 24S)-3beta-bromo-5,22,23-trihydroxy-5alpha-stigmastan-6-one (21), were obtained through a synthetic route based on regioselective Delta(5) epoxidation. Compounds 17 and 18, bearing a 5alphaH moiety, were prepared through a reductive opening of the 5beta,6beta epoxy precursor, and compounds 20 and 21, analogs with a 5alphaOH moiety were obtained by hydrolytic opening of a mixture of 5alpha,6alpha and 5beta,6beta epoxy precursors. Known compounds 19 and 22 were also obtained following the described synthetic routes, respectively. The new compounds were tested with the traditional auxin-like bioassay for brassinosteroids with 19 and 22 as standards. All compounds were comparatively evaluated for their inhibitory effect on the replication of DNA (HSV-1) virus.

Effects on Bioactivity due to C-5 Heteroatom Substituents on Synthetic 28-Homobrassinosteroid Analogs

Abstract Five new 28-homobrassinosteroids have been synthesized, namely, (22 R ,23 R )-5-fluoro-3α,22,23-trihydroxy-5α-stigmastan-6-one, (22 R ,23 R )-5-fluoro-3β,22,23-trihydroxy-5α-stigmastan-6-one, (22 R ,23 R )-5-fluoro-2α,3α,22,23-tetrahydroxy-5α-stigmastan-6-one, (22 R ,23 R )-3α,5,22,23-tetrahydroxy-5α-stigmastan-6-one and (22 R ,23 R )-3β,5,22,23-tetrahydroxy-5α-stigmastan-6-one. Their bioactivities were evaluated by the rice lamina inclination test. C-5α Fluorinated analogs showed excellent in vitro bioactivity, also revealed at low doses, while C-5α hydroxylated analogs resulted in an important decrease in bioactivity. Previously given explanations to justify the decreasing effect due to C-5α electronegative groups should be revised.

Carotenoids from three red algae of the corallinaceae

Abstract The carotenoid composition of the red algae Corallina officinalis , Corallina elongata and Jania sp. were analysed. The same eight compounds were isolated and identified from the three species: β-carotene, zeaxanthin, fucoxanthin, 9′- cis -fucoxanthin, fucoxanthinol,9′- cis -fucoxanthinol and the epimeric mutatoxanthins. The latter two components are described for the first time as natural products from the marine environment. The results allowed us to infer that Corallinaceae are able to produce de novo allenic and epoxy carotenoids, contrary to the general supposition that their presence in the algae was due to colonizing organisms.

Biosynthesis of bufadienolides in toads: III—Experiments with [2-14C]mevalonic acid, [20-14C]3β-hydroxy-5-pregnen-20-one and [20-14C]cholesterol☆

The biosynthesis of bufadienolides in Bufo paracnemis toads has been studied in different seasons of the year using [2-14C]mevalonic acid, [20-14C]pregnenolone, and [20-14C]cholesterol as precursors. The results showed that the doubly unsaturated δ-lactone ring of the bufadieno-lides is directly derived from the cholesterol side chain without the compounds prior conversion into pregnenolone. The probable sequence in which the different bufadienolides are formed is discussed.

Biosynthesis of the bufadienolide marinobufagin in toadsBufo paracnemis from cholesterol-20-14C

Der biogenetische Ursprung des Marinobufagins in KrötenBufo paracnemis wurde durch Injektion von Cholesterol-20-14C nachgewiesen. Durch Abbau wurde festgestellt, dass die Gesamtaktivität des Produktes im C-20 des Marinobufagins enthalten ist.

Enzymatic deacetylation of steroids bearing labile functions

Abstract Lipase from Candida cylindracea and Candida antarctica catalyzes the removal of acetyl groups from 3β-acetoxypregn-5-en-20-one and 3β-acetoxy-20-(S)-hydroxycholest-5-en-23-one through a transesterification reaction in organic solvents.

Synthesis of 6-deoxy-4-O-methyl-d-galactose (d-curacose)

Abstract The stereospecific synthesis of 6-deoxy-4- O -methyl- d -galactose has been accomplished by using somewhat different intermediates in two related ways. The synthetic sugar is shown to be identical with d -curacose, a constituent of the antibiotic curamycin. Some of the known compounds used in the syntheses have been prepared by improved methods.

Cardenolide glycosides from the roots of mandevilla pentlandiana

Abstract From the roots of Mandevilla pentlandiana 13 cardenolide-type compounds were isolated. Besides free aglycones digitoxigenin and oleandrigenin, the structures of mono-, tri-, tetra- and pentaglycosides of both genins were characterized by means of chromatographic and spectroscopic methods.

Conformations of some per-O-acetylaldononitriles and 5-(polyacetoxyalkyl)tetrazoles

The conformations of several per-O-acetylaldononitriles and 5-(polyacetoxyalkyl)tetrazoles in pyridine-d5 solution have been studied by p.m.r. spectroscopy. For compounds of both types, those having the arabino, galacto, and manno configurations take an extended, planar, zigzag arrangement for the carbon chain, whereas, for those having the xylo, ribo, and gluco configurations, the values of the coupling constants indicate that a bent conformation is favored.