6 research outputs found
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 āgreenā
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 BāC
bond cleavage and facile protonolysis of a AuāĻ-phenyl
intermediate
An Experimental and in Situ IR Spectroscopic Study of the LithiationāSubstitution 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 lithiationāsubstitution 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 ā50 Ā°C for 5ā30 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 lithiationāsubstitution of <i>N</i>-Boc-2-phenylpyrrolidine at ā78 Ā°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 <sup>1</sup>H NMR spectroscopy. For the pyrrolidine, the half-life (<i>t</i><sub>1/2</sub>) for rotation of the Boc group was found
to be ā¼10 h at ā78 Ā°C and ā¼3.5 min at ā50
Ā°C. In contrast, for the piperidine, <i>t</i><sub>1/2</sub> was determined to be ā¼4 s at ā78 Ā°C
An Experimental and in Situ IR Spectroscopic Study of the LithiationāSubstitution 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 lithiationāsubstitution 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 ā50 Ā°C for 5ā30 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 lithiationāsubstitution of <i>N</i>-Boc-2-phenylpyrrolidine at ā78 Ā°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 <sup>1</sup>H NMR spectroscopy. For the pyrrolidine, the half-life (<i>t</i><sub>1/2</sub>) for rotation of the Boc group was found
to be ā¼10 h at ā78 Ā°C and ā¼3.5 min at ā50
Ā°C. In contrast, for the piperidine, <i>t</i><sub>1/2</sub> was determined to be ā¼4 s at ā78 Ā°C