Judgment, Supreme Court, Bronx County (David Stadtmauer, J.) rendered January 20, 1989, *365convicting defendant, after jury trial, of criminal sale of a controlled substance in the third degree, and sentencing him, as a second felony offender, to six to twelve years imprisonment, unanimously affirmed.
Defendant’s conviction arises out of his street sale of one vial of crack cocaine to an undercover police officer, who immediately radioed the seller’s description to his back-up team. Based upon this radioed description, defendant was detained by the back-up officers, and arrested when the undercover officer confirmed that defendant was the crack seller.
Initially, we note that as defendant failed to object to the arresting officer’s testimony regarding the radioed description of the crack seller, which he now claims constituted improper bolstering, his claim is not preserved for appellate review (CPL 470.05 [2]; see also, People v Conyers, 160 AD2d 318, lv denied 76 NY2d 786). In any event, the testimony of the backup officer that he received a radioed description of the individual who had just sold crack cocaine to the undercover officer does not constitute improper bolstering, as it provided a necessary explanation of the events leading up to defendant’s arrest (see, e.g., People v Sarmiento, 168 AD2d 328).
We also note that defendant failed to object to the trial court’s adverse inference charge regarding the undercover officer’s discarding of an envelope upon which he had jotted down a description of the crack seller. Thus, defendant failed to preserve the claim of error for appellant review (CPL 470.05 [2]). In any event, the undercover officer’s hand written notes on the envelope, discarded when the information was transferred verbatim to an official police report, are exempt from the Rosario rule as the " 'duplicate equivalent’ ” of the official report (People v Whitaker, 165 AD2d 775, 776, lv denied 76 NY2d 1025). Concur—Sullivan, J. P., Carro, Rosenberger, Ross and Smith, JJ.