Synthesis and Conformational Characterization of Diketopiperazines Bearing a Benzyl Moiety

Abstract

Diketopiperazines bearing a benzyl moiety with different para-substituents were synthesized and analyzed by 1H NMR spectroscopy. All of these diketopiperazines were found to adopt a folded conformation according to the upfield chemical shift of the cis-proton (cis to the benzyl moiety) due to a shielding effect in the 1H NMR spectra. An intramolecular CH–π interaction appears to be an important factor for the folded conformation due to the effects of para-substituents on the benzyl group.

Microindolinone A, a Novel 4,5,6,7-Tetrahydroindole, from the Deep-Sea-Derived Actinomycete Microbacterium sp. MCCC 1A11207

“…By comparing the 1 H-, 13 C-NMR, MS, and optical rotation (OR) data with those reported in the literature, 18 known compounds were identified as pyrrole-2-carboxylic acid ( 2 ) [ 17 ], cyclo( l -Trp-Gly) ( 3 ) [ 18 ], cyclo- l -Tyr- l -Pro ( 4 ) [ 19 ], cyclo( l -Trp-Gly) ( 5 ) [ 20 ], cyclo( l -Phe-Gly) ( 6 ) [ 21 ], cyclo[ l -(4-hydroxyprolinyl)- l -leucine] ( 7 ) [ 22 , 23 ], cyclo[ l -(4-hydroxyprolinyl)- l -isoleucine] ( 8 ) [ 24 ], cyclo-( l -Pro- l -Val) ( 9 ) [ 25 ], cyclo-( l -Pro-Gly) ( 10 ) [ 25 ], cyclo-( l -Leu- l -Ala) ( 11 ) [ 26 ], cyclo-( l -Val-Gly) ( 12 ) [ 27 ], 5-methyluracil ( 13 ) [ 26 ], dibutyl phthalate ( 14 ) [ 28 ], 4-hydroxyphenylacetic acid ( 15 ) [ 29 ], N -(4-hydroxyphenyl)-acetamide ( 16 ) [ 30 ], ( S )-3-hydroxy-4-(4-hydroxyphenyl)butan-2-one ( 17 ) [ 31 ], 3-hydroxy-4-(4-dihydroxyphenyl)-2-butanone ( 18 ) [ 32 ], and (5-hydroxymethyl-furan-2-yl)-methanol ( 19 ) [ 33 ]. Surprisingly, these 19 compounds were all firstly isolated from Microbacterium species.…”

Interfacial supramolecular biomimetic epoxidation catalysed by cyclic dipeptides

“…We also evaluated CDPs with one or two benzyloxymethyl group side chains (26a-29a) (Table 1, entries [24][25][26][27]. Only CDPs 26a and 28a produced epoxides with low enantiomeric excesses (6% and 5%, respectively) (Table 1, entries 24 and 26).…”

“…20. (3S,6S)-3-benzyl-6-methylpiperazine-2,5-dione26 (13a); White powder. 1 H-NMR (400 MHz, DMSO-d 6 ): δ = 0.40 (d, J = 6.9 Hz, 3H), 2.80 (dd, J = 13.7, 4.9 Hz, 1H), 3.08 (dd, J = 13.5, 5.6 Hz, 1H), 3.53-3.60 (m, 1H), 4.15-4.10 (m, 1H), 7.07-7.15 (m, 2H), 7.14-7.26 (m, 3H), 7.97 (s, 1H), 8.07 (s, 1H).…”

Synthesis of Cross-linkable 2,5-Diketopiperazine Derivatives

“…The combined filtrate was evaporated and the residue was dissolved in ethyl acetate (30 mL) and water (20 mL). The organic layer was washed successively with 20 mL portions of 0.5 N HCl, H 2 O, 0.5 N NaHCO 3 and brine, and dried over MgSO 4 . After filtration and evaporation, the residue was subjected to silica chromatography (ethyl acetate/hexane = 1:1, then 3:2) gave a colorless amorphous mass (0.64 g, 75% N 3 )), 14) Boc-L-Tyr-L-Phe(4-N 3 )-OMe 13 (0.32 g, 0.66 mmol) was suspended in 4M HCl-dioxane (5 mL) and the suspension turned to solution with stirring at room temperature for 2 hours, then concentrated.…”