This contribution describes the first stereospecific synthesis of
24(S)-hydroxyvitamin D2 (1), a metabolite of vitamin D2. This
metabolite acts as a prodrug for 1α,24(S)-dihydroxyvitamin D2
(2), which is under development for treatment of various
diseases characterized by cellular hyperproliferation. The key
step of the synthesis involves the Wittig−Horner olefination of
(S)-2,3-dimethyl-2-triethysilyloxybutyraldehyde (17) and a vitamin D2 phosphine oxide derivative (22). The synthesis of the
requisite aldehyde started with the commercially available
l-(+)-valine and was completed in seven steps. The vitamin D2
phosphine oxide derivative was synthesized in seven steps
starting from vitamin D2.
We
report a water-based approach for making chemically reactive
forms of hemp fibers and employing these materials to fabricate biocomposites
for hydroponic applications. Our chemical strategy focused on coupling
the lignin of hemp fibers and a bifunctional linker molecule (2-[(4-aminophenyl)sulfonyl]ethyl
hydrogen sulfate) that contains an aromatic amine and a protected
vinyl sulfone. The synthetic process started with converting the amine
of this linker to an electrophilic diazonium ion, which then reacted
with the electron-rich aromatic rings of the lignin within the hemp
fibers to form the chemically reactive lignin. The other functional
group of the linker was activated under basic conditions to yield
the intermediate vinyl sulfone, which reacted with poly(vinyl alcohol)
via the Michael addition to yield the cross-linked hemp fiber composites
in a 1 in. diameter quartz tube mold. The overall fabrication process
was ecofriendly because only water was used as the solvent, and harmless
inorganic salts were the only major byproducts. These hemp composites
were durable and did not easily crumble under compressive mechanical
tests. Fabrication experiments were performed with different weight
ratios of bifunctional linkers to hemp fibers to evaluate the effect
of this factor on the mechanical strength of resulting hemp composites.
The compressive strength of these dry hemp composites was measured
to increase from 0.91 to 1.81 MPa when this weight ratio was raised
from 3: 40 to 3: 5. The hemp fiber composites fabricated using an
intermediate weight ratio (3: 10) of the bifunctional linkers to hemp
fibers were evaluated as a hydroponic growth medium. Properties of
the hemp fiber composites, such as water holding capacity, carbon/nitrogen
ratio, salinity, and acidity, were also evaluated to determine their
suitability as plant growth media for hydroponic applications. The
hemp fiber composites were demonstrated to be effective hydroponic
growth media for Daikon radish and green peas in a 14-day growth period.
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