Use of grass seed resources c.31 ka by modern humans at the Haua Fteah cave, northeast Libya

The recovery of a seed grinding stone from human occupation layers dating to c.31 ka in the Haua Fteah cave on the coast of the Gebel Akhdar massif in northeast Libya sheds new light on the subsistence practices of modern humans in North Africa. An integrated study of usewear and organic residue analysis confirms the use of the tool for seed grinding. Residue analysis recovered a total of 15 starch granules that could be reliably identified as belonging to wild cereals, ten of which are identified as A-type granules of Aegilops sp. (goat grass). The results of this study show that modern humans had the capacity to identify large-seeded grasses as a potential food source, perhaps targeted during periods of resource stress, and were capable of adapting pounding and grinding technologies to solve the unique problems of seed processing to render an edible food from grasses. The findings from this research show that broad-spectrum diets involving the exploitation of wild cereals were emerging during the Late Stone Age in North Africa

landscape.data

This folder contains RData objects and R scripts used to carry out the least-cost path analyses described in the m

Gold-Catalyzed Proto- and Deuterodeboronation

A mild gold-catalyzed protodeboronation reaction, which does not require acid or base additives and can be carried out in “green” solvents, is described. As a result, the reaction is very functional-group-tolerant, even to acid- and base-sensitive functional groups, and should allow for the boronic acid group to be used as an effective traceless directing or blocking group. The reaction has also been extended to deuterodeboronations for regiospecific <i>ipso</i>-deuterations of aryls and heteroaryls from the corresponding organoboronic acid. Based on density functional theory calculations, a mechanism is proposed that involves nucleophilic attack of water at boron followed by rate-limiting B–C bond cleavage and facile protonolysis of a Au−σ-phenyl intermediate

An Experimental and in Situ IR Spectroscopic Study of the Lithiation–Substitution of <i>N</i>-Boc-2-phenylpyrrolidine and -piperidine: Controlling the Formation of Quaternary Stereocenters

A general and enantioselective synthesis of 2-substituted 2-phenylpyrrolidines and -piperidines, an important class of pharmaceutically relevant compounds that contain a quaternary stereocenter, has been developed. The approach involves lithiation–substitution of enantioenriched <i>N</i>-Boc-2-phenylpyrrolidine or -piperidine (prepared by asymmetric Negishi arylation or catalytic asymmetric reduction, respectively). The combined use of synthetic experiments and in situ IR spectroscopic monitoring allowed optimum lithiation conditions to be identified: <i>n</i>-BuLi in THF at −50 °C for 5–30 min. Monitoring of the lithiation using in situ IR spectroscopy indicated that the rotation of the <i>tert</i>-butoxycarbonyl (Boc) group is slower in a 2-lithiated pyrrolidine than a 2-lithiated piperidine; low yields for the lithiation–substitution of <i>N</i>-Boc-2-phenylpyrrolidine at −78 °C can be ascribed to this slow rotation. For <i>N</i>-Boc-2-phenylpyrrolidine and -piperidine, the barriers to rotation of the Boc group were determined using density functional theory calculations and variable-temperature ¹H NMR spectroscopy. For the pyrrolidine, the half-life (<i>t</i>_1/2) for rotation of the Boc group was found to be ∼10 h at −78 °C and ∼3.5 min at −50 °C. In contrast, for the piperidine, <i>t</i>_1/2 was determined to be ∼4 s at −78 °C

An Experimental and in Situ IR Spectroscopic Study of the Lithiation–Substitution of <i>N</i>-Boc-2-phenylpyrrolidine and -piperidine: Controlling the Formation of Quaternary Stereocenters

A general and enantioselective synthesis of 2-substituted 2-phenylpyrrolidines and -piperidines, an important class of pharmaceutically relevant compounds that contain a quaternary stereocenter, has been developed. The approach involves lithiation–substitution of enantioenriched <i>N</i>-Boc-2-phenylpyrrolidine or -piperidine (prepared by asymmetric Negishi arylation or catalytic asymmetric reduction, respectively). The combined use of synthetic experiments and in situ IR spectroscopic monitoring allowed optimum lithiation conditions to be identified: <i>n</i>-BuLi in THF at −50 °C for 5–30 min. Monitoring of the lithiation using in situ IR spectroscopy indicated that the rotation of the <i>tert</i>-butoxycarbonyl (Boc) group is slower in a 2-lithiated pyrrolidine than a 2-lithiated piperidine; low yields for the lithiation–substitution of <i>N</i>-Boc-2-phenylpyrrolidine at −78 °C can be ascribed to this slow rotation. For <i>N</i>-Boc-2-phenylpyrrolidine and -piperidine, the barriers to rotation of the Boc group were determined using density functional theory calculations and variable-temperature ¹H NMR spectroscopy. For the pyrrolidine, the half-life (<i>t</i>_1/2) for rotation of the Boc group was found to be ∼10 h at −78 °C and ∼3.5 min at −50 °C. In contrast, for the piperidine, <i>t</i>_1/2 was determined to be ∼4 s at −78 °C

Warmuth et al. PNAS 2012

Warmuth et al. PNAS 201