Dina I.M.D. de Mendonça

Hydroxylated diterpenoids from Halimium viscosum

Several hydroxylated bi- and tri-cyclic terpenoids have been isolated from the aerial parts of Halimium viscosum (Celorico da Beira, Portugal). Together with valparolone, with the same skeleton, two additional compounds have been identified: (4S)-2β-acetoxyvalparol-15-en-3-one and (4S)-2β-acetoxyvalparol-8(14)-en-3-one. Together with the well-known valpara-3(19),15-dien-2β-ol, valpara-1,13-dien-2α-ol and 2β-acetoxyvalpara-4,15-dien-3α-ol, two new compounds have been isolated, belonging to the valparane class, and identified as valpara-3,15-dien-2β-ol and 3α-hydroxyvalpara-4,15-dien-2-one. There are several bicyclic diterpenoids that should be noted: with labdane skeleton; a diformate and the monoformylderivatives of labd-7-en-3β,15-diol and with halimane skeleton the 15-hydroxy-ent-halim-1(10)-en-18,2β-olide. The total composition of the aerial parts of this plant allows the identification of Celorico da Beira Halimium viscosum as a new chemotype.

Hydrohalimic acids from Halimium viscosum

Abstract Several diterpenoid acids, with an ent -halimane skeleton, were isolated from the aerial parts of Halimium viscosum as methyl esters. Besides the well known hydrohalimic acid, acetoxyhydrohalimic acid, cinnamoyloxyhydrohalimic acid and 2-hydroxyhydrohalimic acid, three new ones have been identified as methyl 15- Z -cinnamoyloxy-1(10)- ent -halimen-18-oate, methyl 15-hydroxy-2-oxo-1(10)- ent -halimen-18-oate and methyl 15-methoxy-1(10)- ent -halimen-18-oate. Their structures have been determined by chemical and spectroscopic methods, using 2D correlation experiments ( 1 H 13 C and 13 C 13 C).

BI- and Tricyclic Diterpenoids from Halimium viscosum

Abstract The study of the acid and neutral parts of the n-hexane extract of Halimium viscosum (S. João da Pesqueira, Portugal) has led to the isolation of various known diterpenoids with the ent-halimane skeleton. Five new compounds have now been isolated, one with the ent-halimane skeleton, and four with the valparane skeleton, two of them with the valparane skeleton degraded. The structures of these compounds, determined by spectroscopic methods using 2D experiments (1H-13C, HMQC and HMBC), were dimethyl 1(10)-halimen-15,18-dioate, dimethyl 3,19-dinor-15-valparen-2,4-dioate, methyl 16-nor-2,3-secovalpara-3,15-dioxo-2-oate, 1,3,5,15-valparatetraene and 3R-4α-methoxy-15-valparen-2-one.

Activity coefficients in the evaluation of food preservatives

Abstract Food preservatives are used in very low concentrations. However, usually they are used in aqueous high ionic strength solutions. The Pitzer model allows activity coefficient determination in these cases. Without the knowledge of activity coefficients, activity or ‘correct concentration’ cannot be known. In this work, the activity coefficients of sodium chloride, potassium chloride and calcium chloride in pure solutions were calculated by the Debye–Huckel theory and the Pitzer theory. The calculated values were compared with experimental values. Activity coefficients of pure sodium benzoate in aqueous mixed solutions with potassium chloride or calcium chloride were evaluated using the Pitzer model. The same evaluation can be done to more complex systems once all Pitzer parameters values for the ionic species are known.

Tricyclic diterpenes from Halimium viscosum

Abstract Several tricyclic diterpenes with a valparane skeleton have been isolated from the aerial parts of Halimium viscosum collected at Celorico da Beira, Portugal. Two new compounds have been identified as valpara-2,15-diene-1,4-dione and 3α,4α-epoxyvalpar-15-en-2-one, besides the previously known compounds: valpara-2,13-diene; valpara-2,15-diene; valpara-3,15-dien-2-one; 2β,3β-epoxyvalpar-14-ene and 1β-metoxy-valpara-2,15-diene. Their structures have been established by means of 2D NMR experiments ( 1 H 13 C, and HMQC) and X-ray studies. This plant sample may represent a new chemotype.

Iridoids from Hymenodictyon floribundum

Two new iridoids floribundane A (1) and floribundane B (2) and the known compounds lupenone (3), scopoletin (4) and 4,5-dihydroblumenol A (5) were isolated from trunk bark and leaves of Hymenodictyon floribundum B.L. Rob. The structures of all compounds were established from their spectroscopic data.

8,15-Epoxylabdane and norlabdane diterpenoids from Eragrostis viscosa.

Four labdanes with a 8alpha,15-epoxy ring (8alpha,15-epoxylabdan-16beta-oic acid; 8alpha,15-epoxy-16-norlabdan-13-one; 8alpha,15-epoxy-16-norlabdane; and 16-acetoxy-8alpha,15-epoxylabdane) and the known compound ambreinolide were isolated from the hexane extract of the aerial parts of the grass Eragrostis viscosa. The structures of all compounds were established based on spectroscopic data and the X-ray analysis of 8alpha,15-epoxy-16-norlabdan-13-one. The hexane extract presented moderate activity against the snail Biomphalaria glabrata. 8alpha,15-Epoxylabdan-16beta-oic acid showed no mutagenic activity for doses up to 1000 microg/plate and no significant clastogenic activity for doses up to 100 microg/ml.

Kolbe Electrosynthesis of 1,2-Di(bicyclo[2.2.1]heptan-2-yl)ethane and 1,2-Diphenylethane

Abstract Kolbe electrosynthesis, at low current densities, of 1,2-diphenylethane and 1,2-di(bicyclo[2.2.1]heptan-2-yl)ethane with 77 and 72% yields, respectively, is described.