Aloe resin

Figure 5.13 GALDI mass spectrum of aloe resin (from THF solution). The two doublets correspond to mono and diglucosides of aloe emodin and their oxidation and reduction products, respectively (see Table 5.5)...

Table 5.5 Prominent peaks in the mass spectrum of aloe resin (see Figure 5.13), interpretation following the literature. The dyes are not detected as sodium adducts but as radical cations formed by direct absorption and ionisation of the laser energy...

C Treatment with KOH reagent intensifies the yellow fluorescence of aloin and aloino.sides as well as the blue fluorescence of the aloe resins. Aloe-emodin shows a typical red Borntriiger reaction in UV-365 nra. 

Aloe resins Aloin Aloinosides Aloesins Remarks... 

Nitromatweed (Matweed Nitrate, Nitrosparte in Fr). Prepd by nitration of dried matweed with mixed nitric-sulfuric acids in a manner similar to the prepn of NC. Trench, Faure and MacKie (Ref 2), in 1876, patented expls containing as a base nitrosparte (or other nitrated cellulosic material such as cotton, hay, agave, hemp, flax, straw, aloe, yucca, etc) together with resin, ozokerite, collodion, glycerin, charcoal and soot. Hengst (Ref 3), in 1898, patented a smokeless powd containing nitrosparte prepd by nitration of fibers covering the coconut shell Refs 1) Merriam Webster s Diet, 2nd Ed (1963), ... 

Cleave the Aloe groups (see Notes 6, 7) Add the resin to 1 g (PPh3)4Pd in 10 mL chloroform acetic aciddV-methyl morpholine (37 2 1, v/v/v) and shake for 5 h. Wash the resin 2x with 25 mL 0.5% diisopropyl ethyl amine in DMF, 2x with 25 mL of 0.5% sodium diethyl dithiocarbamate in DMF, and 2x with 25 mL DMF alone. Special reagents needed tetrakis triphenylphosphine palladium diethyl dithiocarbamate. 

N -Protection as allyl carbamate is used generally only for specific synthetic purposes where acid- or base-mediated deprotection procedures must be avoided or reduced to a minimal extent as in the case in the synthesis of glyco- and phosphopeptides (see Sections 6.3 and 6.5). Otherwise the orthogonality of this type of amino protection has been mainly exploited in side-chain protection to allow for selective chemistry such as selective acylations, e.g. cyclizations, to be performed on protected peptides in solution or in the resin-bound state (see Section 4.3.2.3.4). An additional interesting application of the Aloe group is the one-pot deprotection and acylation with carboxy components resistant to the paUadium(0)-catalyzed allyl cleavage by hydrostannolysis as reported in Section 4.3.2.3.4.P 1... 

In terms of stability in the repetitive N -deprotection steps required for the synthesis of larger peptides and proteins, only the Z group and particularly its halogenated derivatives are compatible with the Boc/Bzl strategy for N -protection, while among the other groups discussed in Section 2.1.1.1.1, the Fmoc, Teoc, Msc, and particularly Aloe groups have found application in terms of an additional level of selectivity as required in special cases for postsynthetic site-specific chemical manipulations of the peptide chain on resin or in solution. 

A branched peptide 11 [prothrombin(l-9)-Lys(Leu-enkephalin)-NH2] has been synthesized on a PAL-PEG-PSty resin in a continuous flow peptide synthesizert l by combining A -Fmoc for temporary protection, A -Aloc for semipermanent lysine protection, and Boc for permanent protection of the terminal amino group of prothrombin, as outlined in Scheme 6. Deprotection of Aloe in the continuous flow synthesizer is achieved by use of the Pd(PPh3)4/ NMM/ACOH/CHCI3 system. 

Another example is H-Thr(tBu)-Gln(Trt)-Ile-Asp(OtBu)-Ser(tBu)-Pro-Leu(A -Aloc)-Dap-MBHA-resin, synthesized by the Fmoc strategy.P l Following cleavage of the Aloe group with phenylsilane and tetrakis(triphenylphosphine)palladium, two (aminooxy)acetyl moieties were linked to the a-amino groups of Thr and Dap by reacting the peptide-resin with [(A-Boc-amino)oxy]acetyl A-hydroxysuccinimide ester. 

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