ABSTRACT
Peatlands play a critical role in terrestrial carbon (C) storage, containing an estimated 30% of global soil C, despite occupying only 3% of global land area. Historic management of peatlands has led to widespread degradation and loss of important ecosystem services, including C sequestration. Legacy drainage features in the peatlands of northern Minnesota, USA were studied to assess the volume of peat and the amount of C lost in the ~100 years since drainage. Using high-resolution Light Detection and Ranging (LiDAR) data, we measured elevation changes adjacent to legacy ditches to model pre-ditch surface elevations, which were used to calculate peat volume loss. We established relationships between volume loss and site characteristics from existing geographic information systems datasets and used those relationships to scale volume loss to all mapped peatland ditches in northern Minnesota (USA). We estimated that 0.165 ± 0.009 km3 of peat have been lost along almost 4000 km of peatland ditches. Peat loss upslope of ditches was significantly less than downslope (P < 0.001). Mean width of the entire ditch-effect zone was 333 ± 8.32 m. Using our volume loss estimates, literature estimates of oxidation, and mean bulk density and peat C% values from Minnesota peatlands, we calculate a total historic loss 3.847 ± 0.364 Tg C. Assuming a constant oxidation rate during the 100 years since drainage, euic and dysic peatlands within the ditch effect zone have lost 0.26 ± 0.08 and 0.40 ± 0.13 Mg C ha-1 yr-1, respectively, comparable to IPCC estimates. Our spatially-explicit peat loss estimates could be incorporated into decision support tools to inform management decisions regarding peatland C and other ecosystem services.
Subject(s)
Carbon , Soil , Carbon/analysis , Ecosystem , MinnesotaABSTRACT
An unsaturated dispiro 1,2,4,5-tetraoxane formed by peroxidation of (+)-dihydrocarvone was converted into four structurally diverse derivatives. X-ray crystallographic analysis shows that the structures possess central tetraoxane rings with spiro-2,5-disubstituted cyclohexylidene substituents and 6-membered rings in classical chair conformations. As polarity in the tetraoxane series increased, in vitro potency against Plasmodium falciparum decreased.
Subject(s)
Antimalarials/chemical synthesis , Antimalarials/pharmacology , Tetraoxanes/chemical synthesis , Tetraoxanes/pharmacology , Crystallography, X-Ray , Models, Molecular , Structure-Activity RelationshipABSTRACT
A DFT study of model cyclohexyloxy radicals (8a-c, 9) show that (a) the presence of an adjacent oxygen atom, and (b) alpha-substituents on the cyclohexyl ring, particularly methoxy, accelerate the rate of beta-scission ring-opening reactions. Consistent with theoretical results, thermolysis of the methoxy-substituted dispiro-1,2,4-trioxane 10 afforded the structurally novel, 14-membered macrocyclic keto lactone 11 as the major isolable product.
Subject(s)
Cyclohexanes/chemistry , Cyclization , Free Radicals , Models, Molecular , ThermodynamicsABSTRACT
The iron-mediated reactivity of various dispiro-1,2,4-trioxolanes was determined by automated kinetic analysis under standard reaction conditions. The active antimalarial compounds underwent peroxide bond cleavage by Fe(II) resulting in products indicative of carbon-centered radical formation. The rate of reaction was heavily influenced by the presence of spiro-substituted adamantane and cyclohexane rings, and was also significantly affected by cyclohexane ring substitution. Steric hindrance around the peroxide oxygen atoms appeared to be the major determinant of reaction rate, however polar substituents also affected reactivity by an independent mechanism. A wide range of reaction rates was observed within this class of peroxide antimalarials, however iron-mediated reactivity did not directly correlate with in vitro antimalarial activity.
Subject(s)
Antimalarials/chemistry , Ferrous Compounds/chemistry , Heterocyclic Compounds, 1-Ring/chemistry , Spiro Compounds/chemistry , Adamantane/analogs & derivatives , Adamantane/chemistry , Animals , Antimalarials/pharmacology , Crystallography, X-Ray , Cyclohexanes/chemistry , Heterocyclic Compounds, 1-Ring/pharmacology , Kinetics , Models, Molecular , Plasmodium falciparum/drug effects , Spiro Compounds/pharmacologyABSTRACT
In the competitive peroxidation of mixtures of two alkenes with Co(II)/O(2)/Et(3)SiH, it was found that the relative reactivities of the alkene substrates are influenced by three major factors:. (1) relative stability of the intermediate carbon-centered radical formed by the reaction of the alkene with HCo(III) complex, (2) steric effects around the C=C double bond, and (3) electronic factors associated with the C=C double bond. Consistent with results from simple alkenes, the chemo- and regioselective peroxidation of dienes was also realized. Depending on the diene structure, the product included not only the expected acyclic unsaturated triethylsilyl peroxides but also 1,2-dioxolane and 1,2-dioxane derivatives via intramolecular cyclization of the unsaturated peroxy radical intermediates.
Subject(s)
Alkadienes/chemistry , Antimalarials/chemical synthesis , Artemisinins/chemistry , Peroxides/chemical synthesis , Sesquiterpenes/chemistry , Crystallography, X-Ray , Cyclization , Molecular Conformation , Molecular StructureABSTRACT
Ozonolysis of (alkenyldioxy)cyclododecyl hydroperoxides in trifluoroethanol gave a separable mixture of the corresponding alpha-hydroperoxy- and alpha-hydroxy-substituted spiro-tetraoxacycloalkanes with ring sizes in the range 7-12. Dehydration of the hydroperoxides or oxidation of the hydroxy-compounds afforded the corresponding peroxylactones. The solid-state structure of 1,2,6,7-tetraoxaspiro[7.11]nonadecan-3-one was determined by X-ray crystallographic analysis.
ABSTRACT
Photooxygenation of 2-phenylnorbornene 1 in the presence of 30% aqueous hydrogen peroxide afforded 1,2-bishydroperoxide 3, which could be cycloalkylated on treatment with silver oxide and a 1,omega-diiodoalkane to provide the tricyclic peroxides 12. Trimethylsilylation of 3 followed by TMSOTf-catalyzed cyclocondensation with carbonyl compounds led to the formation of the tricyclic peroxides 14 containing a 1,2,4,5-tetroxepane structure. Photooxygenation of 1 in the presence of either unsaturated hydroperoxides or unsaturated alcohols followed by bis(collidine)iodine hexafluorophosphate promoted cyclization gave the corresponding cyclic peroxides 15-17. Several of these cyclic peroxides showed substantial antimalarial activity particularly in vitro.
Subject(s)
Antimalarials/chemical synthesis , Bridged Bicyclo Compounds, Heterocyclic/chemical synthesis , Peroxides/chemical synthesis , Animals , Antimalarials/chemistry , Antimalarials/pharmacology , Bridged Bicyclo Compounds, Heterocyclic/chemistry , Bridged Bicyclo Compounds, Heterocyclic/pharmacology , Crystallography, X-Ray , Mice , Peroxides/chemistry , Peroxides/pharmacology , Plasmodium falciparum/drug effects , Tumor Cells, CulturedABSTRACT
Iodonium ion mediated cyclization of unsaturated hydroperoxides 1 afforded the expected yingzhaosu A analogues 2. In some cases, however, the corresponding cyclic ethers 5 were formed competitively with the cyclic peroxides 2, the ratios of these two products being a marked function of the structure of the starting materials. Some of the cyclic peroxides 2 showed significant antimalarial activities in vitro and in vivo.
