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Modifications at

The first reported carbohydrate modification at C-2 was the formation of D-glucal (D-glucose with a carbon-carbon double bond between C-1 and C-2) from bro-moacetyl glucose [87]. This led to the synthesis of 2-deoxy-D-glucose on the addition of water to the double bond [88] (reaction 4.75). The optimization and preparative details for the formation of 2-deoxy-D-glucose have been reported [89]. [Pg.108]

The 2-deoxy-a-l-bromide (reaction 4.77) can be used to synthesize 2-deoxy-P-D-glycosides (reaction 4.77) or oligosaccharides, the latter with a 2-deoxy group in the nonreducing residue, as shown in reaction 4.84, to give 2 -deoxycel-lobiose.  [Pg.110]

Potato phosphorylase catalyzes the reaction of D-glucal with an equimolar amount of phosphate to give 2-deoxy-a-D-glucopyranosyl phosphate [92] (reaction 4.85). Reaction of potato phosphorylase with D-glucal, maltotetraose, and catalytic amounts of phosphate gives 2-deoxymaltooligosaccharide [92] (reaction 4.86). When this latter reaction is followed by a reaction with sweet potato P-amylase, 2 Mideoxymaltose is obtained [93] (reaction 4.87). [Pg.110]

Finally, 2 -C-fluoromethyl uridine was synthesized starting from uridine 28 that was protected with a di-tert-butylsilyl group and oxidized at the 2 -position to give the still protected nucleoside 29 030L807 . A Wittig reaction with methyltriphenylphosphonium bromide, followed by a series of protection/deprotections, afforded compound 31. Once again, only examples of pyrimidine nucleosides were given. [Pg.31]


A Acetylation, O-Phosphorylation, and O-Adenylylation. A/-Acetylation, O-phosphorjiation, and O-adenyljiation provide mechanisms by which therapeutically valuable aminocyclitol antibiotics, eg, kanamycia [8063-07-8] gentamicin [1403-66-3] sisomicin [32385-11-8], streptomycia [57-92-1], neomycin, or spectinomycin are rendered either partially or completely iaactive. Thus, eg, kanamycia B [4696-78-8] (50) can be iaactivated by modification at several sites, as shown. The elucidation of these mechanisms has allowed chemical modification of the sites at which the iaactivation occurs. Several such bioactive analogues, eg, dibekacia and amikacin have been prepared and are not subject to the iaactivation hence, they inhibit those organisms against which the parent antibiotics are iaeffective (96) (see Antibacterial agents, synthetic). [Pg.314]

Several aHotropes of black phosphoms have also been reported (2). These include one amorphous and three crystalline modifications. At increasing pressures and temperatures reaching above 1200 MPa (12 kbar) and several hundred degrees, a series of black phosphoms modifications are formed that are characterized by even higher densities (2.70 g/cm ). These include orthorhombic, rhombohedral, and cubic varieties. The black forms have lower reactivity and solubiUty than red phosphoms. [Pg.348]

Although less researched than the 2-position, modifications at the 6-position of intact penems have been reported. Generation of the dianion of the penem (52, R = CH ) using a strong base such as / -butyUithium or lithium diisopropylamide, followed by reaction with electrophiles yields 6-substituted 2-methylpenems in moderate yield (128). The enhanced acidity of the 6-proton in the bromopenem (88) [114409-16-4] h.a.s been exploited to prepare the... [Pg.13]

All of the naturally-occurring monobactams discovered as of this writing have exhibited poor antibacterial activity. However, as in the case of the penicillins and cephalosporins, alteration of the C-3 amide side chain led to many potent new compounds (12). Furthermore, the monobactam nucleus provides a unique opportunity to study the effect of stmctural modifications at the N-1 and C-4 positions of the a2etidinone ring on biological activity. In contrast to the bicycHc P-lactams, these positions on the monocyclic ring system are readily accessible by synthesis. [Pg.62]

The configuration at the chiral centers C-4a, C-5a, and C-12a determine the conformation of the molecule. In order to retain optimum in vitro and in vivo activity, these centers must retain the natural configuration. The hydrophobic part of the molecule from C-5 to C-9 is open to modification ia many ways without losing antibacterial activity. However, modification at C-9 may be critical because steric iateractions or hydrogen bonding with the oxygen atom at C-10 may be detrimental to the activity. [Pg.179]

AH of the reactions considered to be useful in the production of hemoglobin-based blood substitutes use chemical modification at one or more of the sites discussed above. Table 2 Hsts the different types of hemoglobin modifications with examples of the most common reactions for each. Differences in the reactions are determined by the dimensions and reactivity of the cross-linking reagents. Because the function of hemoglobin in binding and releasing... [Pg.162]

Thus the large-scale preparation of pyridoxylated hemoglobin seems to result in mixtures of reaction products. These probably represent modifications at either or both a- and P-antino-terrmnal residues as well as surface lysines. A partial characterization of the mixture has been carried out (74). [Pg.164]

Modifications at this position are described in various other sections. See, for example, the preparation of 2-substituted methylpenams in Section 5.11.3.3.1, the total synthesis of 2-spirocycloalkylpenams in Section 5.11.4.4, and the synthesis of penems in Section 5.11.4.6. [Pg.312]

Modification at the C(7) position of the penam ring system (other than ring opening reactions) has not been extensively studied. It was possible, however, to convert the /3-lactam to a /3-thionolactam in 1% yield as shown in Scheme 55 (75JA5628). The deblocking product (73) had greatly reduced antibacterial activity compared to the parent /3-lactam. [Pg.327]

As can be seen from Table 3, only modifications at the 6/3-amino groups have been successful in producing penicillins of medical significance up to this time. Several reviews have dealt with the structure-activity relationship in this area in considerable detail B-80MI51102, B-77MI51106, B-75MI51102) and should be consulted for the actual effects of structural modification on antibacterial activity. [Pg.338]

When the modification is temporary. Twenty-eight people were killed by the temporaiy modification at Flixborough, one of the most famous of all time (Lees, Lo.s.s Prevention in the Proce.s.s Indwstrie.s, 2d ed., Buttei woi th-Heinemann, 1996 p. 2). [Pg.2270]

A client may choose to develop a toller who is qualified, but will need additional or improved equipment and technology to meet the eventual production levels required later in the life of the toll contract. The client may require the toller to make changes or modifications at their plant in order to effectively manufacture a particular product in increasing quantity. Some areas of concern applicable to scale up were listed in Various Points to Consider, Section 3.1. Additional considerations to address in the contract may include ... [Pg.57]

Figure 10-116—cf) values on the basis of Figure 10-113. Figure 10-117—hjp/hL values on the basis of Equation 32 (Ref. 45), with modification at 1/Xjj values less than 0.2 as suggested by Dengler and Addoms. ... [Pg.183]

Commercial A -acetylneuraminic acid aldolase from Clostridium perfringens (NeuAcA EC 4.1.3.3) catalyzes the addition of pyruvate to A-acetyl-D-mannosamine. A number of sialic acid related carbohydrates are obtained with the natural substrate22"24 or via replacement by aldose derivatives containing modifications at positions C-2, -4, or -6 (Table 4)22,23,25 26. Generally, a high level of asymmetric induction is retained, with the exception of D-arabinose (epimeric at C-3) where stereorandom product formation occurs 25 2t The unfavorable equilibrium constant requires that the reaction must be driven forward by using an excess of one of the components in order to achieve satisfactory conversion (preferably 7-10 equivalents of pyruvate, for economic reasons). [Pg.591]


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Modifications at C-5 and Substitution for the Ring Oxygen

Mono-modification at Any One of the C2-, C3-, or C6-Positions

Mono-modification at the C6-Position

Per-modification at the C3-, C2-, or C6-Position

Per-modification at the C6-Position

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