scholarly journals Selective tert-Butyl Ester Deprotection in the Presence of Acid Labile Protecting Groups with Use of ZnBr2.

ChemInform ◽  
2005 ◽  
Vol 36 (1) ◽  
Author(s):  
Ramesh Kaul ◽  
Yann Brouillette ◽  
Zohreh Sajjadi ◽  
Karl A. Hansford ◽  
William D. Lubell
Keyword(s):  
Butyl Ester ◽  
Protecting Groups ◽  
Tert Butyl ◽  
Acid Labile

Synthesis of hydrazine and azapeptide derivatives by alkylation of carbazates and semicarbazones

2012 ◽  
Vol 90 (11) ◽  
pp. 985-993 ◽  
Author(s):  
Yesica Garcia-Ramos ◽  
Caroline Proulx ◽  
William D. Lubell
Keyword(s):  
Butyl Ester ◽  
Protecting Groups ◽  
Tert Butyl

Hydrazine and azapeptide analogs were synthesized effectively by alkylation of alkylidene carbazates and semicarbazones. In comparisons of benzylidene, benzhydrylidene, and fluorenylidene tert-butyl carbazates in alkylations using bases of different pKb character, superior conversion was obtained using the fluorenone derivative. Mild alkylation conditions were found employing Et4NOH as base and used to convert fluorenylidene tert-butyl carbazate into 13 different protected hydrazines. Moreover, racemization was avoided during alkylation of fluorenylidene semicarbazide in the synthesis of aza-propargylglycinylphenylalanine tert-butyl ester, the protecting groups from which could be selectively removed.

Biodegradation of cyclic and substituted linear oligomers of poly(3-hydroxybutyrate)

1995 ◽  
Vol 41 (13) ◽  
pp. 180-186 ◽  
Author(s):  
Helmut Brandl ◽  
Brigitte Aeberli ◽  
Reinhard Bachofen ◽  
Ingrid Schwegler ◽  
Hans-Martin Müller ◽  
...  
Keyword(s):  
Methyl Esters ◽  
Butyl Ester ◽  
Ester Group ◽  
Terminal Group ◽  
Protecting Groups ◽  
Clear Zone ◽  
Tert Butyl ◽  
Hairpin Loops ◽  
End Groups ◽  
Fmoc Group

Cyclic oligo(3-hydroxybutyrate), oligo(3-HB), was synthesized and purified, resulting in oligolides that contained three to seven (R)-3-hydroxybutyrate units (triolides up to heptolides). In addition, linear 3-HB octamers obtained as either tert-butyl or methyl esters were substituted with different end groups at the hydroxy end. The hydroxy terminus was replaced by either a benzyloxy, trifluoroacetoxy, crotonyloxy, (S)-3-hydroxybutyryloxy, or fluorenylmethylcarbonyloxy (FMOC) group. P(3-HB) hairpin loops occurred on the surface of certain regions of the polymer, especially of lamellar crystallites. Cyclic 3-HB oligomers provide a model system for these loops. It is assumed that they provide attachment points for the depolymerizing enzymes. All of the (R)-oligolides tested were degraded except the (R)-triolide. Triolides were not degraded, suggesting that enzymatic attack was prevented presumably by steric hindrance on the rigid ring system. Unsubstituted linear octamers were degraded. Biodegradation was prevented when the hydroxy terminus was protected by the FMOC group, but was not dependent on a free hydroxy terminal group: all other protecting groups did not prevent degradation. Substitution of the carboxy end by a methyl or tert-butyl ester group did not influence biodegradation.Key words: poly(3-hydroxybutyrate), oligolides, biodegradation, clear zone test.

Selectivetert-Butyl Ester Deprotection in the Presence of Acid Labile Protecting Groups with Use of ZnBr2

2004 ◽  
Vol 69 (18) ◽  
pp. 6131-6133 ◽  
Author(s):  
Ramesh Kaul ◽  
Yann Brouillette ◽  
Zohreh Sajjadi ◽  
Karl A. Hansford ◽  
William D. Lubell
Keyword(s):  
Butyl Ester ◽  
Protecting Groups ◽  
Acid Labile

Hafnium(IV) Chloride Catalyzes Highly Efficient Acetalization of Carbonyl Compounds

2019 ◽  
Vol 16 (6) ◽  
pp. 913-920 ◽  
Author(s):  
Israel Bonilla-Landa ◽  
Emizael López-Hernández ◽  
Felipe Barrera-Méndez ◽  
Nadia C. Salas ◽  
José L. Olivares-Romero
Keyword(s):  
Microwave Heating ◽  
Reaction Times ◽  
Protecting Groups ◽  
Catalyst Loading ◽  
Selective Protection ◽  
Highly Efficient ◽  
Aldehydes And Ketones ◽  
High Yields ◽  
Novel Catalyst ◽  
Acid Labile

Background: Hafnium(IV) tetrachloride efficiently catalyzes the protection of a variety of aldehydes and ketones, including benzophenone, acetophenone, and cyclohexanone, to the corresponding dimethyl acetals and 1,3-dioxolanes, under microwave heating. Substrates possessing acid-labile protecting groups (TBDPS and Boc) chemoselectively generated the corresponding acetal/ketal in excellent yields. Aim and Objective: In this study. the selective protection of aldehydes and ketones using a Hafnium(IV) chloride, which is a novel catalyst, under microwave heating was observed. Hence, it is imperative to find suitable conditions to promote the protection reaction in high yields and short reaction times. This study was undertaken not only to find a novel catalyst but also to perform the reaction with substrates bearing acid-labile protecting groups, and study the more challenging ketones as benzophenone. Materials and Methods: Using a microwave synthesis reactor Monowave 400 of Anton Paar, the protection reaction was performed on a raging temperature of 100°C ±1, a pressure of 2.9 bar, and an electric power of 50 W. More than 40 substrates have been screened and protected, not only the aldehydes were protected in high yields but also the more challenging ketones such as benzophenone were protected. All the products were purified by simple flash column chromatography, using silica gel and hexanes/ethyl acetate (90:10) as eluents. Finally, the protected substrates were characterized by NMR 1H, 13C and APCI-HRMS-QTOF. Results: Preliminary screening allowed us to find that 5 mol % of the catalyst is enough to furnish the protected aldehyde or ketone in up to 99% yield. Also it was found that substrates with a variety of substitutions on the aromatic ring (aldehyde or ketone), that include electron-withdrawing and electrondonating group, can be protected using this methodology in high yields. The more challenging cyclic ketones were also protected in up to 86% yield. It was found that trimethyl orthoformate is a very good additive to obtain the protected acetophenone. Finally, the protection of aldehydes with sensitive functional groups was performed. Indeed, it was found that substrates bearing acid labile groups such as Boc and TBDPS, chemoselectively generated the corresponding acetal/ketal compound while keeping the protective groups intact in up to 73% yield. Conclusion: Hafnium(IV) chloride as a catalyst provides a simple, highly efficient, and general chemoselective methodology for the protection of a variety of structurally diverse aldehydes and ketones. The major advantages offered by this method are: high yields, low catalyst loading, air-stability, and non-toxicity.

Synthesis of Optically Active Hydroxyalkyl Cycloheptatrienes: A Key Step in the Total Synthesis of 6,11-Methylene-LXB4

Synlett ◽  
2020 ◽  
Vol 32 (01) ◽  
pp. 45-50
Author(s):  
Udo Nubbemeyer ◽  
Analuisa Nava ◽  
Lukas Trippe ◽  
Andrea Frank ◽  
Lars Andernach ◽  
...  
Keyword(s):  
Carboxylic Acid ◽  
Total Synthesis ◽  
Structure Elucidation ◽  
Butyl Ester ◽  
Optically Active ◽  
Chiral Hplc ◽  
Reaction Conditions ◽  
Acid Product ◽  
Tert Butyl ◽  
Nabh4 Reduction

AbstractStarting from methyl cycloheptatrienyl-1-carboxylate, 6-acylation was successfully achieved employing glutaryl chloride in the presence of AlCl3 under controlled reaction conditions to furnish keto carboxylic acid product. After protection of this keto carboxylic acid as tert-butyl ester, reagent-controlled enantioselective reductions delivered configuration-defined methyl-6-hydroxylalkyl cycloheptatriene-1-carboxylates with up to 80% ee. Whereas simple NaBH4 reduction of the keto carboxylic acid and subsequent lactonization afforded a methyl-6-tetrahydropyranonyl cycloheptatriene-1-carboxylate. Resolution using chiral HPLC delivered the product enantiomers with up to >99% ee Finally, ECD analyses enabled structure elucidation. The products are used as key intermediates in enantioselective 6,11-methylene-lipoxin B4 syntheses.

Facile synthesis of tert-butyl ester of N-protected amino acids with tert-butyl bromide

1993 ◽  
Vol 34 (46) ◽  
pp. 7409-7412 ◽  
Author(s):  
Pierre Chevallet ◽  
Patrick Garrouste ◽  
Barbara Malawska ◽  
Jean Martinez
Keyword(s):  
Amino Acids ◽  
Butyl Ester ◽  
Facile Synthesis ◽  
Butyl Bromide ◽  
Tert Butyl

scholarly journals Crystal structure of 2-(4-allyl-4-methyl-2-oxo-1,4-dihydro-2H-benzo[d]- [1,3]oxazin-6-yl)-5-cyano-pyrrole-1-carboxylic acid tert-butyl ester, C22H23N3O4

2014 ◽  
Vol 229 (2) ◽  
pp. 127-128 ◽  
Author(s):  
Chuanhong Zhang ◽  
Jianguo Lin ◽  
Gaochao Lv ◽  
Yang Cao ◽  
Shineng Luo
Keyword(s):  
Crystal Structure ◽  
Carboxylic Acid ◽  
Butyl Ester ◽  
Tert Butyl

Abstract C22H23N3O4, triclinic, P1¯ (no. 2), a = 6.992(3) Å, b = 8.159(4) Å, c = 18.778(8) Å, α = 92.118(7)°, β = 93.463(7)°, γ = 101.623(7)°, V = 1045.9 Å3, Z = 2, Rgt(F) = 0.0576, wRref(F2) = 0.1778, T = 296 K.

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