Synthesis of N-carbobenzoxyamino acid and peptide pentafluorophenyl esters as intermediates in peptide synthesis

Abstract

stallizes as long needles: mp 38-39°; [a] 2Sd +72°(c 1.0, chloroform); yield 1.14 g (40%).Photolysis of 3-azido-3-deoxy-1,2:5,6-di-O-isopropylidene-a-Dallofuranose.-The above azide (4.85 g) in 1 1. of benzene was irradiated 18 hr after which the solution was concentrated and refluxed with aqueous ether (50 ml). After concentrating to dryness, the syrup was applied to a silica gel column and eluted with chloroform-acetone (15:1 v/v). Progress was followed by tic and the fraction containing the ketone hydrate crystallized from ether-hexane: mp 113-114°; [a] 85d +45°(c 1.0, chloroform); yield 1.6 g (34%). Rt and ir values and mixture melting point were identical with those of an authentic sample. Elemental analysis agreed with calculated values.Registry No.-3-Azido-3-deoxy-l, 2:5,6-di-O-isopropylidene-ct-D-allofuranonse, 21870-78-0.

Enantioselective α‐Allylation of Acyclic Esters Using B(pin)‐Substituted Electrophiles: Independent Regulation of Stereocontrol Elements through Cooperative Pd/Lewis Base Catalysis

“…However, while arylboronic acids and esters are easily accessible the corresponding vinylboron species are more challenging to prepare, as control over the alkene geometry is necessary [6] and their greater susceptibility to protodeboronation can be problematic. [7] One such method involves the use of bifunctional borylated building blocks, which simultaneously combines catalyzed bond formation with the concomitant incorporation of a synthetically versatile vinylboron moiety (Figure 1a). Walsh and co-workers have investigated the reactivity and utility of B(pin)-substituted electrophiles in Pd-catalyzed allylic alkylation reactions and described the factors governing chemoselective allylic alkylation in preference to potentially competing Suzuki–Miyaura cross coupling.…”

Traversing Steric Limitations by Cooperative Lewis Base/Palladium Catalysis: An Enantioselective Synthesis of α‐Branched Esters Using 2‐Substituted Allyl Electrophiles

“…[8] Thep ostulated mechanistic scenario upon which our cooperative catalysis is predicated permits the separation of these two critical features. Further assessment of solvent and reaction time gave the product in excellent yield and enantioselectivity (entries [10][11][12][13][14]. As acontrol, re-evaluation of Xantphos using this in situ catalyst formation protocol was performed.…”

N-Acylation in combinatorial chemistry

“…29 Oligopeptides have been similarly prepared by a stepwise addition procedure. 30 Various N-carbobenzoxyamino acid pentafluorophenyl esters, 31 especially pentafluorophenyl esters of Fmoc-amino acids, 32 have been prepared and fully characterized. A one-pot procedure for the simultaneous N-protection and C-terminal activation of amino acids and thiol carboxylic acids using pentafluorophenyl trifluoroacetate (12) has been reported (Scheme 6).…”

“…64 Reactions with bromotris(dimethylamino) phosphonium hexafluoro-phosphate (BroP) (29), bromotripyrrolidino phosphonium hexafluorophosphate (PyBroP) (30) and chloro tripyrrolidino phosphonium hexafluorophosphate (PyClop) (31) have been compared; in reactions of N-protected amino acids and N-methylated amino acids, peptides were obtained in high yields in 60 min with 0-0.3% racemization, but longer reaction time caused 13-18% epimerization. 65 The reaction of 2-chloro-1,3-dimethylimidazolidium hexafluorophosphate (CIP) (32) was employed with α-aminoisobutyric acid (Aib) (Scheme 14).…”