A simple, convenient, and wide scope protocol for the N-formylation of amino acid esters and primary amines has been developed utilizing only imidazole in warm DMF.
The Tm(3+) chelate of DOTAM [1,4,7,10-tetrakis(carbamoylmethyl)-1,4,7,10-tetraazacyclododecane] possessing sterically demanding t-butyl amide substitution favors TSAP geometry. This chelate displayed a paraCEST signal associated with the highly shifted amide proton signal at approximately -100 ppm that was beyond the frequency of macromolecule magnetization transfer. This signal also displayed high temperature dependence (0.57 ppm °C(-1)) in the range of 35-42 °C and at neutral pH.
Cyclic α-quaternary carbon stereocenters were prepared
from
biselectrophillic substrates and an easily prepared chiral bicyclic
sulfonyl lactam. This was achieved in two steps by spiroalkylation,
employing biphasic reaction conditions with a phase-transfer catalyst,
followed by reduction and alkylation with a series of alkyl halide
electrophiles. The products of this method were isolated in good yields
with with high levels of diastereoselectivity. This methodology was
employed in the enantioselective total synthesis of (R)-puraquinonic acid (1) for a late-stage installation
of the α-quaternary carbon stereocenter. This enabled the shortest
synthesis of 1 to date, an eight-pot sequence providing
an overall yield of 14%.
A series of structurally modified Tm(3+) DOTAM-alkyl complexes as potential PARACEST MRI contrast agents has been synthesized with the aim to decrease the overall positive charge associated with these molecules and increase their biocompatibility. Two types of structural modification have been performed, an introduction of terminal carboxylate arms to the alkyl side chains and a conjugation of one of the alkyl side chains with aspartic acid. Detailed evaluation of the magnetic resonance imaging chemical exchange contrast associated with the structurally modified contrast agents has been performed. In contrast to the acutely toxic Tm(3+) DOTAM-alkyl complexes, the structurally modified compounds were found to be tolerated well during in vivo MRI studies in mice; however, only the aspartic acid modified chelates produced an amide proton-based PARACEST signal.
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