Javier Vallejos

Isolation of cytotoxic diterpenoids from the Chilean medicinal plant Azorella compacta Phil from the Atacama Desert by high‐speed counter‐current chromatography

BACKGROUNDnAzorella compacta (Apiaceae) is a native Chilean cushion shrub which produces a resin containing mulinane and azorellane diterpenoids. This plant has been used since pre-Colombian times to treat inflammation and dental neuralgias. In this work the first preparative fractionation of diterpenoids present in this plant by means of high-speed counter-current chromatography (HSCCC) was applied, and cytotoxic effects of the isolated compounds were evaluated for the first time against a panel of MCF7 cells.nnnRESULTSnThe major compounds isolated were identified by means of spectroscopy as azorellanol, 13α, 14α-dihydroxymulin-11-en-20-oic acid, mulinolic acid, mulin-11,13-dien-20-oic acid, 17-acetoxy-mulin-11,13-dien-20 oic acid, and 17-acetoxy-mulinic acid (compounds 7, 9-11 and 13, respectively), and four minor diterpenoids [7-deacetyl-azorellanol (6), 13-epi-azorellanol, 7-acetoxy-mulin-9,12-diene, and 17-acetoxy-mulin-11,13-dien-20-oic acid (compounds 4, 8 and 12)], together with three new minor diterpenoids: 13β,14β-dihydroxymulin-11-en-20-oic acid (1), 13-epiazorellanone (2) and 13-epi-7-deacetyl-azorellanol (3) were identified. Besides, compounds 4, 6, 7, 8 and 11 displayed good cytotoxic activity (less than 50% cell viability at 100 µM). Among them, compound 7, an acetylated azorellane, was the most active.nnnCONCLUSIONSnHSCCC allowed the isolation of 13 diterpenoids present in A. compacta. Three compounds are reported for the first time. Isolated azorellanes are more potent cytotoxic agents than are mulinanes.

Calibration and Verification of Two Bonded-Particle Models for Simulation of Intact Rock Behavior

Abstract In this study, bonded-particle models were used to simulate the intact rock behavior of Westerly granite. Two three-dimensional models were tested: the enhanced bonded-particle model (EBPM) and the flat-joint contact model (FJCM). To calibrate both models, a new standard procedure was developed. The results of the simulations of the models were compared with the intact rock behavior determined by laboratory tests, including elastic parameters, peak and threshold envelopes, and postpeak behavior. From this study, it can be concluded that the FJCM better represents the mechanical behavior of Westerly granite rock, especially at the low to intermediate confining pressures. Based on this work, it is recommended to use the FJCM to model the behavior of brittle rock at the low to intermediate confining pressures.

Further Mulinane and Azorellane Diterpenoids Isolated from Mulinum crassifolium and Azorella compacta

The new mulinane diterpenoids 1 and 2 were isolated from the EtOAc extract of Mulinum crassifolium, while the rearranged mulinane 5, which was isolated for the first time from a natural source, was isolated from Azorella compacta. Compounds 1–2 were prepared by semi-synthesis thorough acetylation of the diterpene 17-acetoxymulinic acid (3). A mechanism of reaction was proposed, while the structures of the new compounds were elucidated on the basis of comprehensive spectroscopic analysis and computational methods.

Truncated gaussian simulation to map the spatial heterogeneity of rock mass rating

This research was supported by the Chilean Commission for Scientific and Technological Research (CONICYT), through Projects CONICYT/FONDECYT/REGULAR/No 1130085 and CONICYT PIA Anillo ACT1407, and by Innova Chile CORFO 11IDL2-10630.

Concise and Straightforward Asymmetric Synthesis of a Cyclic Natural Hydroxy-Amino Acid

An enantioselective total synthesis of the natural amino acid (2S,4R,5R)-4,5-di-hydroxy-pipecolic acid starting from D-glucoheptono-1, 4-lactone is presented. The best sequence employed as a key step the intramolecular nucleophilic displacement by an amino function of a 6-O-p-toluene-sulphonyl derivative of a methyl d-arabino-hexonate and involved only 12 steps with an overall yield of 19%. The structures of the compounds synthesized were elucidated on the basis of comprehensive spectroscopic (NMR and MS) and computational analysis.

Seismic Parameters of Mining-Induced Aftershock Sequences for Re-entry Protocol Development

A common characteristic of deep mines in hard rock is induced seismicity. This results from stress changes and rock failure around mining excavations. Following large seismic events, there is an increase in the levels of seismicity, which gradually decay with time. Restricting access to areas of a mine for enough time to allow this decay of seismic events is the main approach in re-entry strategies. The statistical properties of aftershock sequences can be studied with three scaling relations: (1) Gutenberg–Richter frequency magnitude, (2) the modified Omori’s law (MOL) for the temporal decay, and (3) Båth’s law for the magnitude of the largest aftershock. In this paper, these three scaling relations, in addition to the stochastic Reasenberg–Jones model are applied to study the characteristic parameters of 11 large magnitude mining-induced aftershock sequences in four mines in Ontario, Canada. To provide guidelines for re-entry protocol development, the dependence of the scaling relation parameters on the magnitude of the main event are studied. Some relations between the parameters and the magnitude of the main event are found. Using these relationships and the scaling relations, a space–time–magnitude re-entry protocol is developed. These findings provide a first approximation to concise and well-justified guidelines for re-entry protocol development applicable to the range of mining conditions found in Ontario, Canada.

Three-dimensional effect of stresses in open stope mine design

Abstract The stability graph method is widely used for open stope mine design. During the development of the method the effect of induced stresses were included by using two-dimensional or limited three-dimensional stress analysis. In this paper, three-dimensional numerical models are used to develop new induced stress curves, and to evaluate the effects on the stability graph method and open stope mine design. Significant differences are identified for the estimated stresses at the wall of the stopes, leading to an increase of the size of the stopes.

Open pit mine planning considering geomechanical fundamentals

Abstract The objective of this study is to integrate the admissible factor of safety (FoS) into the mine planning. The analysis showed, as expected, that a lower net present value (NPV) is obtained with the increase in the admissible FoS. Most importantly, it demonstrated that the FoS of the slopes of the adjacent phases, which are not part of the final pit, are considerably greater than the admissible FoS. Therefore, the NPV of an open pit mine project can be increased by steepening the slopes of adjacent phases that are not part of the final pit walls.