Tips derivatives

Iodopyrroles, such as the TV-TIPS derivative shown in 6.44. couple equally efficiently. Its reaction with a series of acetylene derivatives in the presence of a regular catalyst gave rise to the TV-protected 3-ethynylpyrrole... 

The simplest model describing this mode of drug delivery applies to the low volumetric flow range for small molecules — for example/ cisplatin delivered at 0.9 pL/hr (23). The model is a differential mass balance for a typical shell volume surrounding the cannula tip. Deriving it in the same fashion as in Equation 9.1/ except taking the spherical geometry of the distribution into account/ it is... 

Sodium Azide/Ammonium Cerium(IV) Nitrate. Silyl enol ethers give a-azido ketones on treament with sodium azide and anhydrous ammonium cerium(IV) nitrate in anhydrous acetonitrile (see Eq. 97).297 325 33i With a glycal, the 2-azido-1-hydroxy nitrate derivative is formed.332 Low yields due to hydrolysis of the silyl enol ether may be improved by use of the triisopropylsilyl (TIPS) derivatives,331 although with a sterically encumbered taxane-derived enol ether the TMS derivative gives higher yields than the TIPS derivative.325 The mechanism is believed to involve addition of an azide radical to the double bond. 

Reduction. Reduction of the carboxyl group of an a-amino acid without racemiza-tion can be carried out by the BH3-Me2S complex on its TIPS derivative. 

Thus, 3, 5 -di-0-(/-butyldimethylsilyl)thymidine (211) is sulfonylated by 2,4,6-triisopropylbenzenesulfonyl chloride (TIPS-C1) to furnish the 4-0-TIPS derivative 212 in 93% yield. Amination with 2-(methylam-ino)ethanol gives rise to 72% of 213 (87TL2821). 

Butyldimethylsilyl (TBDMS) [68, 69], diphenyl-f-butylsilyl (DPTBS) [70-72] and tri-c-propylsilyl (TIPS) [73,74] have become the three most useful protecting groups in carbohydrate chemistry. TBDMS, DPTBS and TIPS derivatives are far more stable to hydrolysis than TMS analogs. They are often crystalline compounds, are stable to a variety of reaction conditions [75-82], and do not possess additional stereogenic centers. 

Figure 8.6.7 The hydrophobic Tips derivatives transport many water-soluble derivatives of complementary bases into chloroform.

The p-azidation of the TIPS derivative 474 has been utilized in the total synthesis of the antitumor alkaloid (-l-)-pancratistatin (476). Azide 475, the key intermediate product in this synthetic scheme, was obtained in high yield as a mixture of trans- and c -diastereomers (3.5 1 ratio) and was further converted into pancratistatin (476) in 13 steps (Scheme 3.188) [564,565]. 

Likewise, the P-azidation reaction has been applied to the enantioselective synthesis of the core structure of lycorane Amaryllidaceae alkaloids. The key intermediate 478 in this synthesis was obtained by p-azidation of the TIPS derivative 477 as a mixture of trans- and CM-diastereomers (3.5 1 ratio) (Scheme 3.189) [566]. 

The interlayer distance of the solids generally increases on complex formation, thus indicating that the ligand modifies its interlayer orientation when it gives rise to the coordination. However, a lack of change in the d does not necessarily mean that coordination has not occurred for several y-ZP and y-TiP derivatives, although the XRD patterns do not ow any d ... 

Further examples of the use of the TIPS protecting group allow selective substitutions at the 2,3- and 2 ,3 -hydroxy groups of maltose and cellobiose, respectively, as indicated by the structures (22) and (23) of the main mono-TIPS derivatives of the 1,6-anhydro-... 

High yielding preparations of 2 -C> allylribonucleosides have been described, by allylation of 3, 5 -0-Tips derivatives. Again, phosphoramidites were made for incorporation into oligonucleotides. The uridine derivative 226 was also made by alkylation of a Tips... 

N.m.r. experiments in DjO and DMSO-<4 and molecular mechanics calculations have shown that di-<3-deoxy-3-D-gi ero-pentulose) l,2 2,r- dianhydride (8) is asymmetric with a marked difference in the flexibility of the two furanose rings. Selective deuteration provided efficient markers in the conformational analysis of 2 -deoxyuridine and its 3, 5 -0-Tips derivative H-am.r.-, F.t.i.r.-, and Rarhan-spectroscopy. ... 

Different l,l,3,3-tetraisopropyldisiloxane-l,3-diyl (TIPS) derivatives of methyl a-D glucopyranoside have been used to give access to 1,6- and 1,3-p-linked glucobioses (Scheme 21) in the last case substitution would have been favoured at 0-2 in the absence of the cyclic protecting group. ... 

Fig. 2.5 Charge carrier mobility as a function of inter-molecular distance in 2-phenylnaphthalene (PNP) and tertMophene (TIP) derivatives. The numbers indicates the number of carbons in the side chain...

---