Boc-protected Amines Research Articles

Ruthenium‐Induced Allylcarbamate Cleavage in Living Cells

Organometallics are increasingly gaining attention as tools in chemical biology owing to their distinguished physicochemical properties, reactivities, and three-dimensional structures. Along these lines, the exceptional ability of organometallic compounds to catalyze a wide variety of chemical transformations has not yet been sufficiently exploited for chemical biology, but could yield bioactive molecules with novel properties. For example, such catalysts could eventually be used to amplify signals by turning over a substrate multiple times, catalytically label or deactivate target biomolecules, or release prodrugs and all this in a cellular environment. However, designing catalysts which work under physiological conditions is a significant challenge owing to the combined presence of air, water, and a plethora of cellular components such as millimolar concentrations of thiols, which are prone to poison organometallic catalysts, especially under protic and aerobic conditions. With respect to this new aspect of bioorganometallic chemistry, we herein disclose a ruthenium-catalyzed release of amines from their allylcarbamates that tolerates the combination of water, air, and thiols, and we demonstrate the utility of this cleavage reaction in living mammalian cells. In the course of screening several organometallic catalysts for a variety of reactions, we found that the complex [Cp*Ru(cod)Cl] (Cp*= pentamethylcyclopentadienyl, cod= 1,5-cyclooctadiene; 1) catalyzes the cleavage of allylcarbamates 2 to their respective amines 3 in the presence of an excess of thiophenol in an open flask experiment, tolerating water and air (Scheme 1). 12] For example, the reaction of pmethylaniline allylcarbamate 2a (200 mm) with 5 equivalents of thiophenol in the presence of 10 mol% ruthenium catalyst 1, carried out in MeOH/H2O (95:5) under air and overnight at room temperature, provides p-methylaniline in 86% yield if isolated as the tert-butoxycarbonyl (Boc)-protected amine, and 89% yield according to GC analysis (Table 1, entry 1). This deprotection is quite general as it works under the same conditions with high yields also for allylcarbamates of an electron-acceptor-substituted aniline (2b, 85% yield) and a primary (2c, 94%, isolated as the Boc-protected amine), as well as a secondary amine (2d, 87% yield; Scheme 1). The influence of air, water, and aliphatic thiols on the GCdetermined yields of this ruthenium-catalyzed cleavage is shown for substrate 2a in Table 1. Accordingly, yields are not significantly affected by air and water (Table 1, entries 1–3). In contrast, omitting thiophenol prevents the carbamate cleavage completely in the presence of water and air (Table 1, entry 4). Most importantly for cellular applications, the cleavage reaction can be performed in the presence of aliphatic thiols, such as benzeneethanethiol, with virtually no influence on the yield of the reaction (93%; Table 1, entry 5). However, if performed at room temperature, the aromatic thiol is necessary because substitution for an aliphatic thiol leads to a significant reduction in yield (34%; Table 1, entry 6). Interestingly, increasing the temperature to 37 8C provides the released amine with an improved yield of 67% by using the aliphatic thiol benzeneethanethiol as the only nucleophile. To evaluate the carbamate cleavage under conditions that more closely resemble a physiological environment, the bis[*] C. Streu, Prof. E. Meggers Department of Chemistry University of Pennsylvania 231 South 34th Street, Philadelphia, PA 19104 (USA) Fax: (+1)215-746-0348 E-mail: meggers@sas.upenn.edu Homepage: http://www.sas.upenn.edu/~meggers/

Reductive removal of the Boc protecting group via a DTBB-catalysed lithiation reaction

The DTBB-catalysed lithiation of Boc-protected alcohols, amines and thiols in THF at 0oC led, after quenching with methanol or water, to the recovery of the free alcohols, amines and thiols in short reaction times and in moderate to very good yields. The procedure has been applied to primary, secondary and tertiary alcohols, phenols, secondary amines and primary, secondary and aromatic thiols. This method represents a reasonable alternative to the previously reported deprotection procedures.

Trehalose Click Polymers Inhibit Nanoparticle Aggregation and Promote pDNA Delivery in Serum

Herein, three new glycopolymers have been synthesized via "click polymerization" to promote nucleic acid delivery in the presence of biological media containing serum. These structures were designed to contain a trehalose moiety to promote biocompatibility, water solubility, and stability against aggregation, amide-triazole groups to enhance DNA binding affinity, and an oligoamine unit to facilitate DNA encapsulation, phosphate neutralization, and interactions with cell surfaces. A 2,3,4,2',3',4'-hexa-O-acetyl-6,6'-diazido-6,6'-dideoxy-D-trehalose (4) monomer was polymerized via copper(I)-catalyzed azide-alkyne cycloaddition with a series of dialkyne-amide comonomers that contain either one, two, or three Boc-protected secondary amines (7a, 7b, or 7c, respectively). After deprotection, three water-soluble polycations (9a, 9b, or 9c) were obtained with similar degrees of polymerization (n = 56-61) to elucidate the role of amine number on nucleic acid binding, complex formation, stability, and cellular delivery. Gel electrophoresis and ethidium bromide experiments showed that 9a-9c associated with plasmid DNA (pDNA) and formed complexes (polyplexes) at N/P ratios dependent on the amine number. TEM experiments revealed that 9a-9c polyplexes were small (50-120 nm) and had morphologies (spherical and rodlike) associated with the polymer chain stiffness. Dynamic light scattering studies in the presence of media containing serum demonstrated that 9c polyplexes had a low degree of flocculation, whereas 9a and 9b polyplexesd aggregate rapidly. Further biological studies revealed that these structures were biocompatible and deliver pDNA into HeLa cells. Particularly, 9c polyplexes promoted high delivery efficacy and gene expression profiles in the presence of serum.

Synthesis of analogs of the phenylamino-pyrimidine type protein kinase C inhibitor CGP 60474 utilizing a Negishi cross-coupling strategy

Analogs of 3-{4-[2-(3-chlorophenylamino)-pyrimidin-4-yl]-pyridin-2-yl-amino}-propanol (CGP 60474) were synthesized as useful models for the evaluation of structure–activity relationships of phenylamino-pyrimidine-type protein kinase C inhibitors. The approach involved Pd-assisted cross-coupling as the key step. Negishi-type coupling was performed both with free amino functionalities and Boc-protected amines present and showed that the protection–cross-coupling–deprotection sequence leads to significantly higher yields.

Synthesis of the Benzhydryl Motif via a Suzuki−Miyaura Coupling of Arylboronic Acids and 3-Chloroacrylonitriles

[reaction: see text] A simple two-step procedure for synthesizing functionalized benzhydrylamines is described. The first step involves a Suzuki-Miyaura coupling reaction between arylboronic acids and 3-chloro-3-arylacrylonitriles at 45 degrees C. A variety of boronic acids and substituted acrylonitriles can be used for the reaction. The resulting 3,3-diaryl-substituted acrylonitriles can be converted into their corresponding Boc-protected amines by catalytic hydrogenation.

Multinuclear platinum(ii)–amine complexes containing bis(aminopropyl)dicarba-closo-dodecaborane(12) ligands

Treatment of the bridging bidentate 1,Z-bis(aminopropyl)-1,Z-dicarba-closo-dodecaborane(12)(1,Z-bis(aminopropyl)-1,Z-carborane) ligands of the type 1,Z-[H(2)N(CH(2))(3)](2)-1,Z-C(2)B(10)H(10)(L(1), Z= 7, 5) or (L(2), Z= 12, 6) with two equivalents of trans-[PtClI(2)(NH(3))](-), followed by halogen ligand metathesis with AgOTf and HCl((aq)) afforded the novel diplatinum(II)-amine species cis-[[PtCl(2)(NH(3))](2)L(n)](7(n= 1) or 8(n= 2), respectively). Similarly, the reaction of L(1) or L(2) with the labile trans-[PtCl(dmf)(NH(3))(2)](+) afforded trans-[[PtCl(NH(3))(2)](2)L(n)](OTf)(2)(9(n= 1) or 10(n= 2), respectively) in good yield and purity. However, isolation of the analogous 1,2-carborane complexes was not possible owing to decomposition reactions that led to extensive degradation of the carborane cage and reduction of the metal centre. The mixed dinuclear complex [cis-[PtCl(2)(NH(3))]-L(1)-trans-[PtCl(NH(3))(2)]]OTf (19) was prepared by treatment of the Boc-protected amine ligand 1-[(Boc)(2)N(CH(2))(3)]-7-[H(2)N(CH(2))(3)]-1,7-C(2)B(10)H(10)(L(3), 15) with trans-[PtCl(dmf)(NH(3))(2)](+) to yield trans-[PtCl(NH(3))(2)L(3)]OTf (16), followed by acid deprotection of the pendant amine group, complexation with trans-[PtClI(2)(NH(3))](-), and halogen ligand metathesis using AgOTf and HCl((aq)). A novel trinuclear species containing 5 was prepared by the addition of two equivalents of 15 to the labile precursor cis-[Pt(dmf)(2)(NH(3))(2)](2+) followed by acid deprotection of the pendant amine groups. Further complexation with two equivalents of trans-[PtClI(2)(NH(3))](-) followed by halogen ligand metathesis using AgOTf and HCl((aq)) afforded the triplatinum(II)-amine species [cis-[Pt(NH(3))(2)(L(1))(2)]-cis-[PtCl(2)(NH(3))](2)](OTf)(2)(23). Complexes 7-10, 19 and 23 represent the first examples of multinuclear platinum(ii)-amine derivatives containing carborane cages. Preliminary in vitro cytotoxicity studies for selected complexes are also reported.

Multicomponent Reactions: Synthesis of Spirocyclic Tetrahydropyran Derivatives by Prins Cyclization.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Synthesis and characterization of polymethacrylate-based nitric oxide donors.

A synthetic path for the preparation of methacrylic homo- and copolymers containing secondary amine groups that can be converted into nitric oxide (NO) releasing N-diazeniumdiolates is described. The polymers are obtained by a multistep procedure involving synthesis of methacrylate monomers containing boc-protected secondary amine sites, free radical benzoyl peroxide initiated polymerization, deprotection of the amine sites, and subsequent reaction of the polymers with NO in the presence of sodium methoxide. Monomers with both linear and cyclic pendant secondary amines are examined as polymer building blocks. In most cases, polymers are obtained for both types with compositions that agree well with initial monomer ratios and with number average molecular weights (M(n)) ranging from 1.69 to 2.58 x 10(6) Da. The final N-diazeniumdiolated methacrylic amine polymers are shown to release NO for extended periods of time with "apparent" t(1/2) values ranging from 30 to 60 min when suspended in phosphate buffer, pH 7.4. Total NO loading and release for these materials can reach 1.99 micromol per mg of polymer and is proportional to the amine content of the polymer. It is further shown that by using a dimethacrylate cross-linking agent in conjunction with the various methacrylate amines, suspension polymerization methods can be employed to create small (100-200 microm) polymeric methacrylate microbeads. Such microbeads that can be sequentially deprotected and converted to NO release particles via in-situ diazeniumdiolate formation as carried out for the non-crosslinked polymers.

MULTICOMPONENT REACTIONS: SYNTHESIS OF SPIROCYCLIC TETRAHYDROPYRAN DERIVATIVES BY PRINS CYCLIZATION.

Substituted spirocyclic tetrahydropyranyl mesylates and tosylates have been synthesized in good yields using a Prins-type cyclization of various cyclic ketones, a homoallylic alcohol and either methanesulfonic or p-toluenesulfonic acid under non-aqueous conditions. The mesylates thus produced could then be transformed into the corresponding Boc-protected amines using an efficient two step procedure.

Orthogonal, convergent syntheses of dendrimers based on melamine with one or two unique surface sites for manipulation.

An orthogonal, convergent route for the introduction of substoichiometric numbers of latent surface sites into dendrimers based on melamine is used to prepare targets that display one or two Boc-protected amines on the periphery. Asymmetry is the result of the stepwise incorporation of functionalized and unfunctionalized dendrons onto the triazine cores, a highly selective process due to the different reactivities of the substituted triazines. The routes to the dendrons rely on iterative reactions of the growing dendrons with triazine cores and diamine linkers. p-Aminobenzylamine is used as a linking group to avoid functional group interconversions or protecting group manipulations. Addition of the benzylamine group to the monochlorotriazine of the dendron proceeds cleanly leaving a less reactive aniline for subsequent reaction with trichlorotriazine. The routes to these targets proceed in 5 or 6 linear steps (11 or 12 total steps) in 40% overall yield. The unique surface sites can be deprotected and subjected to additional chemistries. Reaction of the monofunctionalized dendrimer with trichlorotriazine yields the desired dimer, a molecule whose increased size is evident from light scattering and tapping mode atomic force microscopy, and corroborated with computation.

Enhancing reductive cleavage of aromatic carboxamides.

[reaction: see text] A set of aromatic and especially heteroaromatic N-benzyl carboxamides, derived from naphthalene, pyridine, pyrazine, and quinoline, and the corresponding tert-butyl acylcarbamates have been synthesized and studied by cyclic voltammetry with respect to facilitated reduction. The latter undergo regiospecific cleavage of their C(O)-N bonds under very mild reductive conditions with formation of Boc-protected (benzyl)amine in most cases in nearly quantitative yields. Examples of preparative cleavage by controlled potential electrolysis, activated aluminum, and NaBH(4) are given.

Towards synthetic vaccines built on carbohydrate cores

Lipophilic polyfunctional carbohydrate core/templates have been designed and developed for drug/vaccine delivery. Three carbohydrate-based templates containing four protectedN-terminal arms were synthesised from glucose and galactose. Methyl α-D-glucopyranoside was converted to two derivatives bearing a carboxylic acid handle for attachment to solid supports, spacer arms of differing hydrophilicity, and phthaloyl-protected amino groups suitable for peptide chain extension. β-D-Galactopyranosyl azide was converted to a template bearing a carboxylic acid handle and four BOC-protected amines. All the templates were found to be suitable for attachment to solid supports and subsequent cleavage from resins, using either BOC-or FMOC-methodologies.

Synthesis of α-alkyl-α-aminosilanes by rhodium-catalyzed hydrosilylation of Boc-protected vinyl amines

α-Aminosilanes can be readily prepared by rhodium-catalyzed hydrosilylation of Boc-substituted enamines, followed by acidic removal of the Boc group. This convergent approach allows for the rapid synthesis of new aminosilane structures, useful for their bioactivity and unique reactivity.

Conjugate Addition Reactions of α-Aminoalkylcuprates with α,β-Enones and Enals

Deprotonation of Boc-protected amines with sec-BuLi or transmetallation of α-aminostannanes with n-BuLi affords α-aminoalkyllithium reagents which can be converted into α-aminoalkylcuprate reagents with CuCN or THF soluble CuCN·2LiCl. These reagents undergo conjugate addition reactions with α,β-enones and enals. Reagents prepared from 2 equiv. of the α-aminoalkyllithium reagent give higher yields of conjugate adducts than those prepared from RCuCNLi, particularly when insoluble CuCN is employed. When CuCN·2LiCl is used, the two cuprate reagents give comparable yields of 1,4-adducts and the RCuCNLi reagent, economical in α-aminoalkyl ligand, is preferred. The Boc protecting group can be removed with PhOH/TMSCl and the amino ketone isolated as the hydrochloride salt.

Broadband Dielectric Spectroscopy on the Molecular Dynamics in Dendritic Model Systems

Broadband dielectric spectroscopy (10-1−107 Hz) is employed to study the molecular dynamics in a set of dendritic poly(ether amide)s involving three generations. In the amorphous systems a dynamic glass transition is found which scales well with calorimetric data. Additionally, one broadened or two frequency separated secondary relaxations are detected. They are assigned to local fluctuations of the ester, amide, and Boc-protected amine groups. This interpretation is confirmed by IR spectroscopy and calculations of the dipole moment of the fluctuating moieties.

Synthesis of Potentially β-Blocking Practolol Derivatives: (E +Z)-3-[4-(3-Iodoprop-2-enyloxycarbonylamino)phenoxy]-1-(isopropylamino)propan-2-ol

The iodinatied carbamates 3 (E + Z), with potential β-blocking properties, were synthesized. The first route chosen, from 4-aminophenol and the chloroformate β7, had to be abandoned because of the formation of the oxazolidinone 10 during the epoxidation step. The aminoalcohol 17 prepared from the practolol 1 finally gave the target compounds by condensation with the iodoallylic chloroformates 8 (E + Z). The secondary Boc-protected amine function was regenerated without removing the carbamate function situated in the p-postion, by using mild reaction conditions (1 N HCl).

One-pot conversion of azides to Boc-protected amines with trimethylphosphine and Boc-ON

Reaction of azides with trimethylphosphine followed by addition of 2-( tert-butoxycarbonyloxyimino)-2-phenyl-acetonitrile (Boc-ON) at −20 °C and stirring at r.t. for 5 h affords the desired Boc-amines in 87–100% yields. Similar yields are obtained by mixing all components together (azide, Me 3P, and Boc-ON) in toluene or THF.

Synthesis and antitumor evaluation of 2,5-disubstituted-indazolo[4, 3-gh]isoquinolin-6(2H)-ones (9-aza-anthrapyrazoles).

The synthesis and antitumor evaluation of 2, 5-disubstituted-indazolo[4,3-gh]isoquinolin-6(2H)-ones (9-aza-APs) are described. The key intermediates in the synthesis are benz[g]isoquinoline-5,10-diones which are substituted at positions 6 and 9 with groups of different nucleofugacity for SNAr displacements. The initial displacement of fluoride by a substituted hydrazine leads to the pyrazole analogues. Substitution of the remaining leaving group by an amine or BOC-protected amines leads to the 9-aza-APs 12. These analogues were converted into their maleate or hydrochloride salts 13. In two cases, namely, 13x and 13z, sidearm buildup was also employed in the synthetic pathway. In vitro evaluation of 9-aza-APs against the human colon tumor cell line LoVo uncovered for most of the compounds a cytotoxic potency lower than that of DuP-941 or mitoxantrone and comparable to that of doxorubicin. Only analogues 13c, 13n, and 13ff were as cytotoxic as DuP-941. Interestingly, while DuP-941 was highly cross-resistant in the LoVo cell line resistant to doxorubicin (LoVo/Dx), the 9-aza-APs carrying a distal lipophilic tertiary amine moiety in both chains were capable of overcoming the MDR resistance induced in this cell line. The 9-aza-APs show outstanding in vivo antitumor activity against both systemic P388 murine leukemia and MX-1 human mammary carcinoma transplanted in nude mice. At their optimal dosages, congeners 13a-c, 13f, 13n, 13q, 13x, and 13dd were highly effective against P388 leukemia with T/C% of 200-381, while the T/C% value of DuP-941 was 147. In the MX-1 tumor model, 24 compounds elicited percentages of tumor weight inhibitions (TWI) ranging from 50% to 99%. Congeners 13d, 13k, 13l, 13x, 13z, and 13ee emerged as the most effective ones, with TWI% 96, simliar to that of DuP-941 (TWI% = 95). On the basis of their efficacy profile in additional experimental tumors and lack of cardiotoxicity in preclinical models, two congeners have surfaced as potential clinical candidates.

A Practical Synthesis of Geometrically PureN-Boc-Protected Primary Allylic Amines

N-Boc-Protected primary allylic amines are easily prepared from the corresponding mesylates or halides by using di-tert-butyl imidodicarbonate (Boc2NH) and K2CO3 or Cs2CO3 in a Gabriel-type substitution, followed by selective removal of one Boc group with TFA.

A highly selective protocol for the deprotection of BOC-protected amides and carbamates

A BOC-protected amide or carbamate undergoes mild and selective deprotection by treatment with catalytic Mg(ClO 4) 2 in acetonitrile. Simple BOC-protected amines are not affected by these conditions.