Menthyl esterification allows chiral resolution for the synthesis of artificial glutamate analogs

• Kenji Morokuma,
• Shuntaro Tsukamoto,
• Kyosuke Mori,
• Kei Miyako,
• Ryuichi Sakai,
• Raku Irie and
• Masato Oikawa

Beilstein J. Org. Chem. 2021, 17, 540–550, doi:10.3762/bjoc.17.48

• be effective here (Scheme 2). Thus, the esterification mediated by 2-methyl-6-nitrobenzoic anhydride (MNBA, Shiina esterification) [9], followed by chromatographic separation of the diastereomers, successfully generated the (2S)-isomer 9* (tR 7.0 min) and the (2R)-isomer 9 (tR 11.5 min) in 45.3% and

• yield (28%). The carboxylic acid (rac)-19 was then esterified with ʟ-(−)-menthol (8) for a chiral resolution. The reaction was mediated smoothly by MNBA [9] in 85% yield to give a diastereomeric mixture of menthyl esters 20* and 20 after silica gel column chromatography. As shown in Figure 6, the clean

Aminosugar-based immunomodulator lipid A: synthetic approaches

• Alla Zamyatina

Beilstein J. Org. Chem. 2018, 14, 25–53, doi:10.3762/bjoc.14.3

• the corresponding fatty acid using 2-methyl-6-nitrobenzoic anhydride (MNBA) as activating reagent in the presence of the nucleophilic catalysts 4-(dimethylamino)pyridine N-oxide (DMAPO) [89]. Next, the 2-N-Alloc group was cleaved by treatment with Pd(PPh3)4 and dimethylaminotrimethylsilane (TMSDMA

Enduracididine, a rare amino acid component of peptide antibiotics: Natural products and synthesis

• Darcy J. Atkinson,
• Briar J. Naysmith,
• Daniel P. Furkert and
• Margaret A. Brimble

Beilstein J. Org. Chem. 2016, 12, 2325–2342, doi:10.3762/bjoc.12.226

• that final deprotection of the remaining enduracididine protecting groups would take place after formation of the macrocycle. Treatment of linear precursor 116 with modified Shiina macrolactonisation conditions reported by Batey et al. [74] of 2-methyl-6-nitrobenzoic anhydride (MNBA), DMAP and Dy(OTf)3

Total synthesis of the proposed structure of astakolactin

• Takayuki Tonoi,
• Keisuke Mameda,
• Moe Fujishiro,
• Yutaka Yoshinaga and
• Isamu Shiina

Beilstein J. Org. Chem. 2014, 10, 2421–2427, doi:10.3762/bjoc.10.252

• sesterterpene metabolite isolated from the marine sponge Cacospongia scalaris, has been achieved, mainly featuring Johnson–Claisen rearrangement, asymmetric Mukaiyama aldol reaction and MNBA-mediated lactonization. Keywords: aldol reaction; astakolactin; lactonization; MNBA; terpenoids; Introduction

• already developed the synthetic method of lactones with various ring sizes using 2-methyl-6-nitrobenzoic anhydride (MNBA) under mild reaction conditions in the presence of a nucleophilic catalyst such as 4-(dimethylamino)pyridine (DMAP) [25][26]. By using this method, we have demonstrated that unusual

• total synthesis of compound 1 by exploitng the MNBA-mediated lactonization for the formation of its 8-membered lactone moiety. Results and Discussion The rationalized synthesis of 1 primarily involved the linear synthesis of the prenyl chain precursor from commercially available (E,E)-farnesol to form

A macrolactonization approach to the total synthesis of the antimicrobial cyclic depsipeptide LI-F04a and diastereoisomeric analogues

• James R. Cochrane,
• Dong Hee Yoon,
• Christopher S. P. McErlean and
• Katrina A. Jolliffe

Beilstein J. Org. Chem. 2012, 8, 1344–1351, doi:10.3762/bjoc.8.154

• temperature. Similar yields and low epimerization (52% isolated yield, 6% epimer observed) were obtained using 2-methyl-6-nitrobenzoic anhydride (MNBA) [24] as the activating agent in place of 2,4,6-trichlorobenzoyl chloride. To investigate whether the ΨMe,Me'Pro would assist macrolactonization, linear

• good yields by using either modified Yonemitsu conditions or similar conditions, in which the 2,4,6-trichlorobenzoyl chloride activating agent was replaced with MNBA. Slow addition of the linear seco-acid to the activating agents was found to be the key factor to minimizing epimerization of the C