6213-89-4Relevant articles and documents
Structure-Proving Syntheses of the Polyenoyltetramic Acids Pyranonigrin J and I
Brückner, Reinhard,Drescher, Christian
supporting information, (2022/03/14)
The polyenoyltetramic acids pyranonigrin J (3) and pyranonigrin I (4) had been isolated from Aspergillus niger. Their origins from and roles in biosynthesis as well as the S-configurations of their stereocenter had been deduced from expression experiments with modifications of the corresponding gene cluster. We corroborated this stereochemical assignment after executing the first total syntheses of both compounds because they had essentially the same specific rotations as their natural counterparts. Our syntheses used the β-ketothioester 18 as a conjunctive reagent. It was combined with the l-serine derivatives (S)-19 or (S)-21 (“Western building blocks”), respectively, through aminolyses. Stille couplings with the stannane 13 (“Eastern building block”) followed. The resulting β-ketoamides (S)-11 and (S)-12 underwent desilylative Lacey-Dieckmann cyclizations when exposed to 8 equiv. of Bu4NF. They rendered the polyenoyltetramic acids (S)-26 [acidolysis: → (S)-3] and (S)-4, respectively.
Structure-Elucidating Total Synthesis of the (Polyenoyl)tetramic Acid Militarinone C §
Brückner, Reinhard,Drescher, Christian,Hamburger, Matthias,Keller, Morris,Potterat, Olivier
supporting information, (2020/03/30)
The (polyenoyl)tetramic acid militarinone C (1) heads a family of seven members. Before our work, the configuration of C-5 was unknown whereas the configurations of C-8′ and C-10′ were either (R,R) or (S,S). We synthesized the four stereoisomers of constitution 1, which conform with these insights. This included cross-coupling both enantiomers of the western building block (8) with both enantiomers of the eastern building block (9). The specific rotations of the resulting 1 isomers suggested that natural 1 is configured like the coupling partners (S)-8 and (R,R)-9. This conclusion was corroborated by degrading natural 1 to alcohol 35 and by proving its configurational identity with synthetic (R,R)-35.
Borylation and rearrangement of alkynyloxiranes: A stereospecific route to substituted α-enynes
Fuentespina, Ruben Pomar,De La Cruz, José Angel Garcia,Durin, Gabriel,Mamane, Victor,Weibel, Jean-Marc,Pale, Patrick
supporting information, p. 1416 - 1424 (2019/07/10)
1,3-Enynes are important building blocks in organic synthesis and also constitute the key motif in various bioactive natural products and functional materials. However, synthetic approaches to stereodefined substituted 1,3-enynes remain a challenge, as they are limited to Wittig and cross-coupling reactions. Herein, stereodefined 1,3-enynes, including tetrasubstituted ones, were straightforwardly synthesized from cis or trans-alkynylated oxiranes in good to excellent yields by a one-pot cascade process. The procedure relies on oxirane deprotonation, borylation and a stereospecific rearrangement of the so-formed alkynyloxiranyl borates. This stereospecific process overall transfers the cis or trans-stereochemistry of the starting alkynyloxiranes to the resulting 1,3-enynes.
